Correcting for the underreporting of drug use in opinion surveys.

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The International Journal of the Addictions, 26(9), 945-961, 1991

Correcting for the Underreporting of Drug Use in Opinion Surveys Ian McAllister Department of Politics University College University of New South Wales Canberra, ACT 2600, Australia

Toni Makkai Law Department Research School of Social Sciences Australian National University Canberra, ACT 2600, Australia

Abstract Survey data is one of the major mechanisms for measuring patterns of drug use across populations. But because drug use can be both a legal and an illegal activity, the accuracy of self-reported measures of use has been a continual problem. The sealed booklet questionnaire overcomes these problems by guaranteeing the respondent some degree of anonymity. This paper reports results from a modified booklet method used in a drug use survey with a national population sample. The method produces better estimated than direct questions, yet guarantees the respondent anonymity. In addition, the analysis shows that underreporting for different drugs is behaviorally motivated rather than drug-specific. The results suggest that adults are more concerned about potential use, while adolescents are more concerned about past use.

945

Copyright 0 1991 by Marcel Dekker, Inc.


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McALLISTER AND MAKKAI

Accurately estimating drug use within a general population remains one of the most difficult problems in epidemiology (Mott, 1987). When direct questions about drug use are asked by interviewers in opinion surveys, underreporting is often a major problem (Midanik, 1982). With illicit drugs such as marijuana, heroin, or cocaine, respondents may underreport actual usage because they fear that legal action may be used against them, or because of fears that employers, friends, or family members will gain access to the information. Even when a drug is legal, underreporting may still occur because of the social stigma attached to it, again resulting in inaccurate or misleading estimates of drug use (Walsh and Hingson, 1987) (see Note 1). To try and deal with these problems, a variety of methods have been devised, some of which have relied on indirect indicators of use (Hughes, 1980; Edwards, 1981). With licit drugs, such as alcohol and tobacco, total consumption within the population may be measured by revenue or sales data. However, such data cannot be linked to particular individuals, thereby restricting analyses examining how individual characteristics correlate with use (Johnston, 1989). Even when consumption levels can be matched to areal units, which in turn can be related to census or other aggregate data which will give social structural indicators, there is no certainty that the drug is being consumed by individuals who live within that area (see Note 2). Other indirect indicators of illicit drug use are equally problematic. Police statistics on crime or data on customs seizures have many disadvantages, not least that they often reflect patterns of activity by the enforcement agencies, not real changes in use cross the population (Johnston, 1989). In any event, they can rarely be linked to individual characteristics. Notification statistics in Britain do provide an indication of the overall trend in addiction, but only a minority of addicts are notified (Mott, 1987; Ashton, 1987). Mortality and morbidity data are often used, but they tend to measure the prevalence of extreme cases only, and convey little about use within a general population (Johnston, 1989; Plant, 1989) (see Note 3). For most research on drug use, some form of direct questioning of respondents remains the only feasible method for collecting data (see Note 4). Survey researchers have devised various ways to ask respondents direct questions about drug use in order to improve accuracy. Some of these involve treating the question in a casual way (“Do you happen to have used.. .?”), or linking it with what other people do so that the individual does not feel that their behavior is atypical (“As you know, many people have.. .. How about yourself?”). Other methods use numbered cards to elicit accurate responses (“Will you please read off the number on this card.. .?”) (Barton, 1958). These approaches have several drawbacks, the most important being that they do not guarantee the respondent anonymity (Hoinville and Jowell, 1978). This is especially important when the questions concern illicit drug use. In dealing with threatening questions, a number of interview methods which attempt to provide anonymity have been tried-self-administered questionnaires,


UNDERREPORTINGOF DRUG USE

941

telephone interviews, and random response are three well-known methodologies (see Note 5). The randomized response procedure has two major drawbacks. first, it results in the loss of personal information about the respondent, making it impossible to look at certain types of behavior by socioeconomic characteristics. Thus, the data have a limited role in policy formation. Second, the sample sizesneed to be very large if any multivariate analyses are to be undertaken (Bradbum and Sudman, 1979). In the case of self-administered questionnaires, there is always the issue of completion rates. In comparing four different interview methods (face-toface, telephone, randomized response, and self-administered), Bradburn and Sudman (1979) concluded that self-administered questionnaires did not reduce underreporting of “socially undesirable acts,” and completion rates were the lowest for this methodology. To try and overcome the problems associated with direct questions on sensitive issues, sealed booklets have been used (Hakim, 1979). This is most evident in the United Kingdom and Australia where self-administered census questionnaires can be handed back to the census collector in a sealed envelope. This technique guarantees the respondent some anonymity by ensuring that the collector does not see the responses to particular questions. However, the disadvantage for leave-behind or “drop-off” questionnaires is the lower rate of response, particularly in noncensus surveys where compliance is not legally enforceable. In this paper we report results using a version of the sealed booklet approach in a face-to-face interview, which guarantees the respondent greater anonymity, yet does not risk the lower response rates associated with the leave-behind booklet or self-administered questionnaire (see Note 6 ) .In addition, we use responses to direct questions and to the sealed booklet to show patterns of underreporting in the lifetime prevalence of drug use and the potential for drug use that exists within the Australian population.

METHOD In March and April 1988, a national survey on drug use and attitudes toward drug use was conducted throughout Australia as part of the federal government’s National Campaign Against Drug Abuse (NCADA); full details of the sampling procedure and methodology are given in the Appendix. The survey included two sets of questions about drug use. Both drug use sections asked the respondent to give their experiences with 13 specific drugs. The first section of the questionnaire, delivered by the interviewer, asked the respondent three questions relating to each of the 13 drugs: whether or not they had been offered the drug in question; had tried it; and whether or not they would try it if it was offered to them by a trusted friend. The 13drugs and the way in which they were described to the respondent are listed in the Appendix.


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McALLlSTER AND MAKKAI

The second drug use section consisted of a sealed booklet which was handed to the respondent by the interviewer. The instructions to the respondents asked them to report the same information about their drug experiences as was elicited from the face-to-face questions, with additional information about frequency of use, consumption, if they had injected themselves with any drugs, and how honest they had been in answering the questions. Respondents were asked to give their answers to these questions by calling out numbers to the interviewer. It was made clear to the respondent in the introduction to the booklet that the numbers, ranging from 4 to 409, were jumbled. To emphasize anonymity, it was stressed that the interviewer was not aware what answer the respondent was giving to a particular question, as they had only a sheet of numbers on which they circled the response that the respondent gave. The placement of some questions within the overall framework of a questionnaire has been shown to affect responses. To determine whether any bias in the drug use measures was associated with question position, half of the sample was randomly selected to answer the sealed questions prior to the face-to-face questions, and half after the face-to-face questions.

COMPARING DIRECT QUESTIONS AND SEALED QUESTIONS The survey permits us to examine the differences between the responses to direct questions about drug use and responses to the adapted sealed booklet questions. In presenting the results, we exclude four of the 13 drugs-alcohol, tobacco, quadrines, and ecstasy-on the grounds that alcohol and tobacco are widely used and respondents have few inhibitions about reporting use, while quadrines were a fake drug to test the level of inaccurate responses, and ecstasy proved to be used by hardly any of the respondents. Questions relating to whether or not the respondent had been offered particular drugs are also excluded to simplify the presentation of results and because our primary interest is in past and potential use. Based on the responses to the direct questions and to the sealed booklet, we can identify three types of responses. First and not unexpectedly, the bulk of the respondents answered consistently between the two questions, either positively or negatively. A second group of respondents are those who will have had experiences with some of the drugs, or wish to use them, but who sought to conceal this fact during the course of the interview. In some cases respondents will obviously give consistently negative replies, and thus fall into the first type of response. However, others will give negative responses in the face-to-face question but give positive (and more truthful) responses to the sealed booklet questions. These respondents are identified as attempting to conceal their drug experiences. The third group are those respondents who give positive responses to the sealed booklets questions but negative responses to the face-to-face questions. As they have little logical reason to do so, their responses are treated as random error.



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Table 1 shows the pattern of replies for lifetime prevalence and potential use of the nine drugs across the Australian population as a whole (see Note 7). Overall, the results suggest that the sealed booklet questions yield higher and therefore we presume more accurate estimates of lifetime prevalence and potential drug use within the population. Although the extent of underreporting is not substantialwith the exception of tranquilizers, only 1 or 2%of the population-it is statistically significant, particularly in the case of potential use. We would expect this underreporting to be concentrated among certain demographic groups. In particu-

Table 1 Consistency in Reported Lifetime Prevalence of Drug Use by Method of Questi0ninga.b Percent Inconsistent (Percent tried) Consistent Lifetime prevalence: Painkillers Tranquilizers Marijuana Barbiturates Hallucinogens Amphetamines Cocaine Inha1ents Heroin

80 83 97 94 98 98 99 99 99

Potential use: Painkillers Tranquilizers Marijuana Barbiturates Hallucinogens Ampehtamines Cocaine Inhalents Heroin

74 89 94 96 96 97 98 99 99

Conceal

Random

11

10

13 I 3 2 2

4 2 3 I 0

1

0 0 1

I 0

10 6 4 3 3 2 1 1 1

15 5 2 I 1 1 0 0 0

Conceal-Randoinc

+I +9* -1 0 +I*

+2* +I

+I -1 -5" +1

+2 +2* +2* +I* +I* +1* +I

=Source: 1988 NCADA Community Survey, population sample (weighted N = 1,823). bRanked by the percent who reported trying or potentially wing the drug; this estimate is averaged between the face-to-face question and the sealed booklet. Categories are defined as follows. Consistent: respondents who gave the same answer to the face-to-face question and to the sealed booklet. Concealed: respondents who replied positively to the sealed booklet, negatively to the face-to-face. Random: respondentswho replied negatively yo the sealed booklet, positively to the face-tdace. Figures may not sum to 100 due to rounding. See text for details of question and wording. CMcNemar tests between the concealed and randomed groups, * significant at p < .01.


950


lar, we would expect underreporting to be greatest among groups which are most at risk from a drug. To test this, the estimates were made for different age and sex categories. For example, research has shown that tranquilizer use is concentrated among the middle-aged and among women, and it is these respondents who should most want to conceal their use of the drug. This is supported by the data. The results indicated that while adolescents had a figure +2 for tranquilizer concealment, those over 40 years of age had a more substantial figure of + 11. Similarly, women scored + 12 compared to +7 for men. Similarly, concealment of potential marijuana use was concentrated among adolescents: they scored +7 compared to zero for those aged 40 years or over. The results therefore gave strong circumstantial support to the greater accuracy of the results from the sealed booklet method.

PATTERNS OF UNDERREPORTING To what extent are there patterns of underreporting of drug use across the population? The existence of such a pattern could take one of two forms. first, there is the possibility that it clusters around particular drugs. For example, respondents concerned about admitting details of their cocaine experiences in the interview could conceal details about past as well as potential cocaine use. Second, respondents could be concerned less about particular drugs than about concealing the fact that they had tried them at some point in time, or concealing that they would try a range of drugs if offered by a friend. In other words, the pattern of underreporting could either be drug-specific or it could be behaviorally motivated insofar as it is related to particular behavioral aspects of drug use. To identify patterns of underreporting across the population, factor analysis is applied to the nine drugs for lifetime prevalence and potential use (see Note 8). In each case the variable is scored zero if the respondent is consistent in his or her replies, .5 if randomly inconsistent, and 1 if they attempted to conceal past and potential drug use. Since we would expect different factors to influence responses among different age groups, the analyses are conducted separately for adults and adolescents. For adults, there is a clear pattern of concern about potential use of a wide variety of mainly illicit drugs. In this sense it is the behavioral pattern that is being concealed, not the actual drugs themselves. The first factor in Table 2 indicates that six drugs load together to form one distinct group, including inhalants, cocaine, heroin, and hallucinogens. Marijuana also loads on this factor, but the loading is weaker than that for the other drugs. This general concern for concealing potential use of these drugs includes seven of the nine drugs, the remaining two drugs being both licit drugs, painkillers and tranquilizers. The second factor identifies a group of five drugs, again all illicit, this time headed by amphetamines. Three other fac-

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Table 2

Factor Loadings for Underreporting of Drug Use, Adu1tsa.b


Factor loadings (decimals omitted)

Inhalents, potential user Cocaine, potential user Heroin, potential user Hallucinogens, potential user Amphetamines, potential user Barbiturates, potential user Marijuana, potential user Amphetamines, used Hallucinogens, used Cocaine, used Heroin, used Barbiturates, used Tranquilizers, potential user Painkillers, potential user Marijuana, used Painkillers, used Tranquilizers, used

I

If

79 75 74 66 65 58 53

-11 21

-01 05 12 05

IV

Y

09

-02 01 02 01

04

01 -06 -11 14 -14

-01

00

-1 1

04

23

06 -0 1

06 02

04

71 69 66 50 48

-15 -11 42

-12 -08

17 14 -07 -44 -16

26 12 08

1-05 25

61 55 -41

01 24 15

01 -06 -01

00

-02 12

-15 24

82 60

-12 14

-03

04 -01 14 -05 12

14

Inhalents, used Eigenvalues Percent variance explained

I1

3.5 19.6

2.0 11.1

-0 1 05

05 13 20

09

*

9

_Be

1.2 6.7

1.1 6.1

1.o 5.8

‘Source: 1988 NCADA Community Survey, adults aged 20 or more only (weighted N = 1,652). bVarimax rotated factor loadings from a principal components factor analysis with unities in the main diagonal.

tors emerge, but they are of lesser importance, and in the case of the final factor, includes the use of just one drug, inhalants. A different pattern emerges when we analyze adolescents (Table 3). Here the pattern is more diverse, producing seven factors, but nevertheless the first factor is easily interpretable. It includes five drugs and, in common with adults, it is concerned with behavior rather than specific drugs. In contrast to adults, the predominant concern is with concealing past use of the drugs; four of the drugs are illicit, but the factor also includes tranquilizers. The second factor identifies potential use of three drugs, tranquilizers, inhalants, and cocaine, while the third factor is also concerned with potential use, in this case involving amphetamines, barbiturates, and hallucinogens. The remaining factors are less clear, statistically or theoretically, and the sixth and seventh factors identify single items, marijuana and inhalant use, respectively.

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McALLISTER AND MAKKAI Table 3 Factor Loadings for Underreporting of Drug Use, Adolescentseb ~~

~~~


Factor loadings (decimals omitted) 1

11

111

IV

v

VI

VII

Cocaine, used Amphetamines, used Heroin, used Barbiturates, used Tranquilizers, used

71 69 68 60 53

00

-10 -05

-04

04 -04

03

00 01 -02

05 20 41 - 19

-06

04

Tranquilizers, potential user Inhalents, potential user Cocaine, potential user

01

-10 -06

30

-04 07 12

-03 -08 51

03 07 -09

10 -05

00

-01

-05

06 26

00

76 70

-07

20

30 07 -07 -06 -01 08

-03

06 -01

06

60

11

01

07 32 -38

Amphetamines, potential user Barbiturates, potential user Hallucinogens, potential user

08 -04 02

19 08 -05

77 66 58

- 19

- 14

09 23

48 07

Painkillers, user Painkillers, potential user Hallucinogens, used

12

- 17

04

09 01 01

-01

06

77 61 46

-09

-11

43

-13 22 41

22 -03

-22

Heroin, potential user Marijuana, potential user

-11 20

13 05

12 -14

16 -14

64 62

-08 43

16 -06

Marijuana, used

-05

-03

-02

01

-01

85

04

Inhalents, used

a

46

44

m

_12

4L

L9

2.6 14.5

2.1 11.5

1.4 8.0

I .4 7.6

1.3 7.1

1.2 6.4

1.o 5.8

Eigenvalues Percent variance explained

-

09

Gource: 1988 NCADA Community Survey, adolescents aged 14 to 19 only (weighted N = 434). b V a h a x rotated factor loadings from a principal components factor analysis with unities in the main diagonal.

These results enable us to discern patterns of underreporting of drug use among adults and adolescents in the survey, and they reveal a different emphasis between the two groups. Although both focus on behavior, the main adult pattern in underreporting is the potential use of illicit drugs. Since most of the adults who say they have tried these drugs will have had experiences with them many years in the past, the perceived risk in admitting past use will be minimal. By contrast, the risks in admitting that they would take illicit drugs if they were offered to them in the future are greater, and may involve risks to family or social relationships, or to their job. The net results is that they conceal these views about potential use in the survey. For adolescents, the reverse is the case: if they have tried a particular drug, it will have been in the recent past, perhaps within the previous year, and they will see


95 3

this as a greater risk than admitting potential use. As a consequence, their first priority is to conceal past, not future, use.


WHO UNDERREPORTS DRUG USE? The results from the factor analyses indicate distinct patterns of underreporting of past and potential future drug use among adults and adolescents (see Note 9). By using these measures as dependent variables and applying ordinary least squares (OLS)regression techniques, we can identify the groups within the population who are most likely to conceal their drug use. In theory, each of the 18 variables used in Tables 2 and 3 could be used as dependent variables. In practice, however, the factor analyses showed distinct patterns of clustering between the variables, so a more parsimonious solution is to combine variables identified by the factor analyses; this, in turn, solves the problem of skewness-as some variables have only 1 or 2% of the population concealing drug use-since combining variables produces a larger distribution of respondents on the scale. Substantively meaningful scales were constructed by combining the variables in the first two factors only in Tables 2 and 3, and among these variables, selecting only those with a loading of .60 or more on the factor in question (see Note 10). Full details of reliabilities for the four scales that were used, together with details of their construction, are given in the Appendix. Table 4 shows standardized (beta) regression coefficients predicting the probability of concealment of past drug w e (lifetime prevalence) and potential drug use, separately for the adult and adolescent samples (see Note 11). In addition, we exclude respondents who were consistent in their reporting of all nine drugs between the face-to-face and the sealed booklet questions. In each of the four models, the proportion of the variance explained, shown by the R2 value, is relatively small, ranging from 1to 15%.In that sense, the major influences on underreporting are to be found in factors external to the 10dependent variables included in the regression model. Nevertheless, a variety of influences are consistently important. Among the social structural variables, age is important in two of the four models. For adults, concealing lifetime prevalence is more likely to occur among younger respondents, while among adolescents it is more likely to take place among older respondents. Educational attainment is significant for adolescents, with those possessing lower levels of attainment more likely to underreport their drug use, net of other things. In a society where one in 10 is an immigrant from a non-English speaking country, birthplace has potentially important consequences. However, it is significant only for adults in predicting past drug use, and Australians are more likely to conceal information in the survey than immigrants. Finally, gender is important in only one model, again lifetime prevalence among adults, and here men are more likely to underreport than women.


954 Table 4

Predicting Underreporting in Lifetime Prevalence and Potential Drug Use among Adults and Adolescents (regression estimates)a.b ..~

Standardized regression coefficients


Adults Lifetime (1)

Social structure: Gender Agc Non-English speaking Education Labor force Interview: Comfortable Honest, sealed questions Honest, direct questions Spouselparent present Placement of sealed questions

Rz (adjusted) (N)

Adolescents Potential (2)

.11**

.oo

-.14**

.05 -.02 -.02

0.07* .02

- .04

.04

-.04

.oo

.06 -.31** -.05

4 .I5 (740)

.02 -.16** -.07*

..a .03 (736)

Lifetime (3)

-.06 .34** -.03 -.20* -.03 -.I2 -.03 -.26** -.03

iQ5 .I0

(153

Potential (4) -.03 .I2 -.07 -.07

- .09

.07 .03 -.16* .06 __ -.09 .01 ( 166)

USource: 1988 NCADA Community Survey, adults (total weighted N = 1,673)and adolescents (total weighted N = 434). QLS regression analysis showing standardized regression coefficients (betas) predicting lifetime prevalence and potential drug use, for adults and adolescents separately. In each case the analyses exclude respondents who were totally consistent between the direct and scaled booklet questions on all nine drugs. The dependent variables in columns (1) and (2) are modified versions of factors 1 and 2, respectively, in Table 2, and those in columns (3)and (4)are modified versions of factors 1 and 2, respectively, in Tahle 3. See Appcndix for details of variahles and scoring. **Statistically significant at p < .01, *p .05.

As well as objective measures, the survey contained a range of perceptual items relating to the context of the interview. Several of these variables are important in the regression analysis. The most consistent and strongest influence is whether or not the respondent reported that they had been dishonest in answering the face-to-face questions. Since this question was placed within the sealed booklet, it enabled the respondent to answer the question with complete anonymity. If the respondent admitted dishonesty, then they were significantly more likely to conceal past and potential drug use in the survey. This further reinforces the reliability of our measure of concealment, since it correlates strongly with the respondent’s own perception of what information they had concealed. The perceived honesty of the respondent in the sealed booklet question, as well as how comfortable

UNDERREPORTING OF DRUG USE

955


they felt during the interview, has little impact, as does the presence of a spouse or parent during the interview, with the exception of potential use among adults. Finally, the actual placement of the sealed booklet in the interview schedule is not significant.

The underreporting of drug use in surveys is a perennial problem for researchers. In this paper we have reported results from a method based on the sealed booklet technique. Like the standard sealed booklet method, it guarantees the respondent anonymity in their answers while ensuring an adequate response rate. Our results suggest that the technique produces superior estimates of lifetime prevalence and potential drug use in comparison to conventional direct questions delivered by an interviewer. While it is impossible to quantify the accuracy of the method, we present strong circumstantial evidence, and not least the respondents’ own admission of dishonesty, to indicate that it corrects for the systematic underreporting of drug use in sample surveys. Perhaps the best application of the technique is in large-scale population surveys where questions relating to drug use are likely to encompass a sizable proportion of the population. Our results show that estimates of the lifetime prevalence of tranquilizer use, particularly among acknowledged risk groups such as the middleaged and women, and potential marijuana use among adolescents, increase with the use of the sealed booklet technique. It is these groups, interviewed in their own homes, perhaps with a spouse or parent present, who might be expected to be most reticent in responding truthfully to such questions. The use of this method at least partly mitigates the problems inherent in administering direct questions in such situations. Moreover, the method is simple to use, is not overly time-consuming, and requires little extra staff training. The results also suggest distinct patterns in the information respondents seek to conceal about their past and potential drug use. For both adults and adolescents, the focus is on behavioral aspects of drug use rather than on particular drugs. This accords with studies which show the widespread prevalence of polydrug use, so that if an individual has had experience of one illicit drug, there is a strong probability that they will have had experience with other drugs. A concern with cocaine use, for example, will be closely linked to concern with heroin or marijuana. For adults, potential illicit drug use is a major consideration in underreporting; by contrast, among adolescents the main concern is the admission of past use. As we argue, these differences are perfectly logical, and they reflect relative priorities at different stages of the lifecycle. Finally, more research needs to be conducted on the problems of underreporting and systematic bias in drug use surveys. Only when we have a clear indication of the extent of bias in our research techniques can attempts be made to remedy it. It


956

is important that these new methodologies become widely known and used. This is especially the case in large-scale government surveys, where the sponsors may be unaware of the difficulties in measuring the behavior in question. As Johnston (1989) concludes, it is in these instances that government officials should utilize the skills of specialists working in the field.


APPENDIX Data. The survey was a national population sample involving a systematic quota sample of all dwellings in urban centers with a population of at least %,oOO people and resulted in 2,255 interviews. To select the household member to be interviewed, a systematic procedure based on the age and gender of all people in the house was used. An oversample of 14 to 19 year olds was obtained by interviewing a 14 to 19year old in the house if one was available. Weights are applied to the data based on region, age, and sex, but since the weighted N is adjusted to the true N , significance tests are not affected. Full details can be found in Social Science Data Archives (1989). Questionnaire. The 13 drugs about which information was collected in the survey, together with some “street”names, which were also given in the questionnaire, were as follows: 1. Marijuanalhash

2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Tobacco/cigarettes Heroin Barbiturates Alcohol Tranquilizers Glue/petrol/solvent/rush to sniff Amphetamines (speed) Cocainelcrack Hallucinogens (LSD/magic mushrooms/trips) Painkillers, analgesics Quadrines Ectasy/designer drugs

The first section of the questionnaire, delivered by the interviewer, asked the respondent three questions relating to each of the 13 drugs: 1.

2. 3.

“Have you ever been offered ...?”Just answer “yes” or “no” “Have you ever tried .?” “If a friend you trust ofered you.. ., would you take it?”

..

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UNDERREPORTING OF DRUG USE Tahle 5

Variables, Scoring, and Means= _____~

Meansb


Adults (1)

(2)

(3)

(4)

From a low of 0 to a high of 1

.04 N.A.

N.A. .04

.04 N.A.

N.A. .06

I = male, 0 = female Years 1 = yes, 0 = no

.48 44.8 .I6

SO 45.3 .I6

.41 16.5 .08

16.6 .07

Years 1 = yes, 0 = no

9.9 .57

9.9 .56

9.0

.49

9.2 .50

1 = very, .67 = quite, .33 = not very, 0 = not at all 1 = totally, .67 = mostly, .33 = not very, 0 =

.90

.89

.82

35

.96

.96

.89

.86

.96

.96

.89

.86

.I7

.17

N.A.

N.A.

N.A.

N.A.

.19

.I9

.48

.5 I

.44

.48

(740)

(736)

(155)

(166)

Variables

scoring

Drug use:c Lifetime prevalence Potential use Social structure: Gender Age Non-English speaking overseas born Education Labor force Interview: Comfortable during interview Honest during sealed drug questions

Adolescents

.48

not at all Honest during direct drug questions Spouse present during interview Parent present during interview Placement of sealed questions (N)

1 = yes, 0 = no

1

Q

early, 0 = late

=Source: 1988 NCADA Conununity Survey, adults (total weighted N = 1,673) and adolescents (total weighted N = 434). bAdoleseents are respondents aged 14 to 19, adults aged 20 and over. The means for columns (1) to (4) refer to the regression equations presented in columns (1) to (4)in Table 4. CScales based on the factor analyses in Tables 2 and 3, see text for details.


95 8


The second section of the questionnaire relating to drug use began as follows: The interviewer does not have a copy of this sheet of questions and answers. All the interviewer does have is a list of numbers on the questionnaire. Because we MUST have information on the extent of drug use and the communities attitudes to drugs, please answer the following questions honestly. Just call out the numbers to the interviewer. We repeat, the interviewer does not know either the questions or the answers. To guarantee this, you will note that the numbers have also been jumbled. Your cooperation in this important national health research is greatly appreciated. Have you ever been offered any of the following? (PLEASE CALL OUT THE CORRESPONDING NUMBER FOR “YES” OR “NO” FOR EACH DRUG. For example, if you have ever been offered Alcohol, call out 117. On the other hand, if you have never been offered hallucinogens, call out 74). The 13 drugs were then listed, together with numbers ranging from 4 to 409, presented in a jumbled fashion, matching “yes” and “no” responses. Subsequent questions asked whether the respondent would take the drug if it was offered by a trusted friend, whether they had tried any of the drugs, and if so, when it had last taken place, and how often they took the drug at that time. Definition and Coding of Variables. The variables figuring in the regression analysis are shown in Table %,together with their scoring and means. The scales of variables identified by the factor analyses in Tables 3 and 4 were constructed by simply combining the items in question and then dividing the sum by the total number of items. Since the individual items were scored from zero to 1, this resulted in a similarly scored scale. The reliabilities (Cronbach’s alpha) for the scales were as follows: adults, lifetime use (.79) and potential use (.60); adolescents, lifetime use (.66) and potential use (.5 1). Missing values are treated by the “pairwise present” procedure. Finally, because of missing values, the reported Ns of respondents differ slightly between the analyses.

ACKNOWLEDGMENT The authors gratefully acknowledge the financial assistance of the Australian Commonwealth Department of Community Services and Health, who sponsored the research through a grant from the National Drug Information Centre.

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NOTES 1. Overreportingis also a problem; for example, it is known that young males frequently overreport alcohol use. However, the problem is less significantthan underreportingand is not consideredin this report. 2. A good example of this problem is the 'drive-in bottle shops" found in Australia, selling alcohol. since the customers are predominantly car-driversor their passengers, alcohol may frequently be driven away and consumed in another area, rendering an ecological analysis of such data useless. 3. There has, however, been some success in using multiple indicators of drug use as a means of early detection of trends in drug use, as, for example, in the United States Drug Abuse Warning Network (DAWN) system. Mott (1987) has argued that a similar 'indicator" system in Great Britain is 'the most feasible, quickest and least costly way of regularly monitoring the number of problem drug takers in an area" (Mott, 1987, p. 13). 4. There are a variety of different survey designs which can be implemented. Johnston (1989) gives an excellent overview of these approaches. 5 . The randomized response technique was originally proposed by Warner (1965; see also Greenberg el al., 1969; Folson, 1973). 6. A similar technique was used in a survey of drug use in Adelaide in 1978 (Heine and Mant, 1979). 7. Moat of those who concealed their use, or potential use of a drug, did so with one drug only. Across the total population sample, 75% were consistent across all nine drugs on past use, while 20% concealed past use of one drug. Only I% concealed use of two or more drugs, the bulk of them (4%) two drugs. Figures for potential use are similar. 8. Since the purpose of the factor analysis is to identify an underlying structure between the variables, it emphasizes groups of variables which are similar to one another. The actual order of the factors merely reflects this pattern of similarity; it does not imply that underreporting is greater for one variable (or groups of variables) than for another variable. 9. For results which show that underreporting tranquilizers and marijuana use is concentrated within particular demographic groups, see Makkai and McAllister (1992). 10. Preliminary analyses and estimates of scale reliabilities (Cronbach's alpha) for the other factors indicated that the reliabilities were low, typically less than .20, and for that reason they were not included inthe final analysis.The decision to exclude variables loading less than .60on the factor was taken for the same reason. The reliabilities for the existing scales are given in the Appendix. 11. Because our interest lies in the relative importance of the independent variables within a particular equation, we report standardized (beta) rather than partial (b) coefficients. Since beta coefficients have been standardized to the mean of the variable in question, they are not comparable between equations.

REFERENCES ASHTON, M. (1987). Treatment trends: The statistics tell the story. Drugfink pp. 12-13, September/ October. BARTON, J. A. (1958). Asking the embarrassing question. Public Opin. Q. 22: 67-68. BRADBURN, N., and SUDMAN, S.(1979). Iiiiproving Interview Method and Questionnaire Design. San Francisco: Jossey-Bass. EDWARDS, G . (1981). The home office index as a basic monitoring system. In G. Edwards and C. Busch (eds.), Drug Problem in Britain: A Review of Ten Years. London: Academic Press. FOLSON, R. E., et al. (1973). The two alternate questions randomized response model for human surveys. J. Am. Stat. Assoc. 68: 125-530. GREENBERG, B. G., et al. (1969). The unrelated question randomized response model theoretical framework. J. Ant. Stat. Assoc. 6 4 120-539.


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HAKIM, C. (1979). Ccnsus confidentiality in Britain. In M. Bulmcr (cd.), Censuses, Surveys and Privacy. New York Holmes & Meicr. HANUSHEK,E. A., and JACKSON, J. A. (1977). Statistical Methodsfor Social Scientists. New York: Academic Prcss. HEINE, W., and MANT, A. (1979). Drug use in Adelaide 1978, Research paper 4. In Royal Commission into the Non-Medical Use of Drugs South Australia, Three Studies in Drug Use. Adelaide: Royal Commission into the Non-Medical Use of Drugs. HOINVILLE, G., and JOWELL, R. (1978). Survey Research Practice. London: Heinemann. HUGHES, P. H. (1980). Core Data for Epidemiological Studies of Nonmedical Drug Use. Geneva: World Health Organisation. JOHNSTON, L. D. (1989). The survey technique in drug abuse assessment. Bull. Narc. 91: 29-40. MAKKAI, T., and McALLISTER, I. (1992). Asking scnsitive questions h presonal interviews: The use and validity of the sealed booklet method. SOC. Indicators. Forthcoming. MIDANIK, L. (1982). The validity of self-rcported alcohol consumption and alcohol problems: A literature review. Br. J. Addict. 77: 357-382. MO'IT, J . (1987). Assessing prevalence. Druglink pp. 12-13, March/April. NEWCOMB, M., MADDAHIAN, E., and BENTLER, P. (1986). Risk factors for drug use among adolescents: Concurrent and longitudinal analyses. Am J. Public Health 86: %25-531. PLANT, M. (1989). The epidemiology of illicit drug-use and misuse in Brihin. In S. MacGregor (cd.), Drugs and British Society. London: Routledge. SOCIAL SCIENCE DATA ARCHIVES (1989). NCADA Coininunity Survey 1988. Canberra: Australian National University Social Scicnce Data Archive. WALSH, D., and HINGSON, R. (1987). Epidemiology and alcohol policy. In G. Levhe and A. Lilienfield (edq.), Epidemiology and Health Policy. London: Tavistock. WARNER, S.M. (1965). Randomizcd response: A survey technique for eliminating evasive answer bias. J. Am. Stat. Assoc. 60: 63-69.

THE AUTHORS Ian McAllister is Professor of Politics, University of New South Wales, and was previously a Senior Research Fellow in sociology in the Research School of Social Sciences at The Australian National University, Canberra, and a Research Fellow at the Centre for the Study of Public Policy, University of Strathclyde, Glasgow. His interests include the sociology of drug use, political behavior, and socioeconomic aspects of ethnicity. His two most recent books are The Loyalties of Vofers(London: Sage, 1990, with Richard Rose) and Australian Political Facts (Melbourne: Longmans, 1990).



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Toni Makkai is a National Research Fellow in the Research School of Social Sciences at The Australian National University, Canberra. She has a PhD in sociology from the University of Queensland. She is currently working on a major study of the sociology of drug use in Australia, with particular reference to the policy issues associated with drug use in the community. Her most recent publication is Perceptions and Patterns of Drug Use (Canberra: Australian Department of Community Services and Health, 1989), coauthored with Ian McAllister and Rhonda Moore.

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