44
The Health Belief Model: Evaluation of a Diabetes Scale ANN C. HURLEY, RN, DNSc Edith Nourse Rogers Memorial Veterans Hospital
Bedford, Massachusetts
Scales that make theoretical
concepts of
health beliefs operational must be shown to have acceptable levels of reliability and validity before they can be incorporated into teaching programs. This paper describes the process used to evaluate a Health Belief Model scale. A revised 11-item scale is proposed for use by diabetes educators. Content validity of the initial scale (76 items) and the shorter version was verified. Reliability estimates obtained by factor structure provided evidence of measurement accuracy for the proposed 11-item scale. Analyses of construct and criterion validity provided additional support to suggest the use of the HBM11 scale for clinical practice.
Fundamental beliefs are strong motivators of human behavior. One strategy to promote self-care success with managing the diabetes regimen is for clinicians to devise an educational plan based on these beliefs. An accurate link must exist between the theoretical belief, which is abstract, and the world of practice, which is concrete. The belief must be made operational and expressed in objective terms before it can be applied to patient teaching. Then an accurate assessment of individuals’ beliefs can be conducted to guide the educational intervention. A number of scales are available for assessing the beliefs of individuals who have diabetes, but the caution of &dquo;buyer beware&dquo; must be exercised. In some respects, selection of a scale for a practice setting can be like buying an outfit from a mail-order catalog. It might fit perfectly, need a few alterations, or sit unused in the back of the closet. The same scrutiny that one applies to product evaluation and the selection of diabetes equipment should be applied to selecting a scale for clinical practice. Questions such as: What should it do? What are its specifications ? How has it worked previously’? need to be answered. Norbeck’ has suggested that answers to these questions be included in reports that describe instrument development. Consumers should be given a complete report of the conceptual basis of the scale, how the instrument was constructed, and its psychometric properties. This paper evaluates a scale that operationalized the Health Belief Model for individuals who have diabetes. The evalua-
Dr Hurley is Nurse Researcher/Project Director, Geriatric Research Education and Clinical Center, Edith Nourse Rogers Memorial Veterans
Hospital. An earlier version of this paper was presented at the Fifth Phyllis J. Verhonic Nursing Research Course sponsored by the United States Army Nurse Corps, April 1988. This study was supported in part by an individual National Research Service Award (#5F31NR0593) from the National Center for Nursing Research, National Institutes of Health; a clinical research grant from Alpha Chi Chapter, Sigma Theta Tau International; scholarships from the Leroy E. Dettman Foundation and the Reserve Officers Association of the United States; and tuition assistance from the United States Army. Reprint requests to Ann C. Hurley, RN, DNSc, 61 Babcock Street, Apt
3-A, Brookline, MA 02146. Downloaded from tde.sagepub.com at UNIV OF MASSACHUSETTS on March 16, 2015
45
tion process was conducted by application of the Norbeck criteria’ to answer the following reliability and validity
questions. 1. Does the scale have content validity’? 2. Does the scale have adequate reliability estimates by internal consistency and retest stability? 3. Does the scale have construct validity according to its factor structure? 4. Does the scale have adequate criteria-related estimates of concurrent and predictive validity’?
the hypothesized clusters. Six final clusters were declared to be stable and reproducible, but the criterion validity of the HBM76 was not examined. Becker and Janz&dquo; suggested that a shorter version of the HBM76 scale be used, and they identified 16 items to represent the HBM. Four items were selected to stand for each dimension: perceived susceptibility, severity, benefit, and barrier. The Becker and Janz scale will be referred to as the HBM 16. Content
Related Literature Basis The Health Belief Model (HBM) is a framework for understanding individuals’ psychological readiness to take health actions. The social psychologists who developed the model had a phenomenological orientation, that is, perception of reality rather than reality itself determines what individuals will or will not (lo.2 An individual’s evaluation of the goal and conviction that a given action would achieve the goal constitute the conceptual framework
Conceptual
underlying the HBM. Personal beliefs of perceived susceptibility to and seriousof the health condition of note, and perceived benefits of action weighed against barriers to action are considered the major dimensions of the HBM. The combined action of the distinct beliefs of the HBM is an integral part of its theoretical foundation.33 Since the HBM is concerned with belief; that can be changed, the model has been used as a framework to guide many and diverse health behavior invesiigaiion;.4 outpatient pilot. (’’) an inpatient pilot, and (3) a prospective study that included an inpatient and follow-up component. The investigator recruited all potential subjects. The purpose, procedures, risks, and benefits were explained, and patients who agreed to participate provided written informed
Procedures
an
consent.
The outpatient pilot test was conducted to examrne the stability of the scale without creating a situation that might alter the very beliefs the scale made operational. To accurately test the stabilit) of the HBM 16, it was necessary to seek subjects who currently had stable diabetes, whose treatment plan had not recently changed, and for whom neither were expected to change in the near future. Those criteria were assumed to be present in outpatients who had been seen in the clinic within
the past 6 months and who were not scheduled for an rnpatient admission. For the test component, potential subjects were mailed a packet of materials consisting of the instructions, consent form, and the study iiiatei-lais. The 38 patients who had responded to the inmal mailing were sent the second packet of materials. Twenty-seven subjects’ participated in the retest phase. The mean duration between test and retest waa ??
days.
The HBM 16 incorporated a five-point Likert scale in which subjects selected a number from one to tive (strongly agree, agree, undecided, disagree, or strongl~ disagree) to indicate their belief in the statement. High scores equate with psychological readiness to undertake diabetes health actions. Strong agreement with positively worded items representing perceived susceptibility, seriousness, benefit, and low barriers was scored as tive. Negatively worded items were reverse scored.
Other Measures Diabetes information and demographic data were available in the medical record. Glycosylated hemoglobin (HbAr) levels were determined at the clinic visit or when subjects were admitted to the inpatient unit and were available in the medical record. HbA, was measured by use of the G1~ trac system (distributed by Corning Medical, Corning Glass Works). The nondiabetic range is 5.~‘’~ to 7.4% . To examine the HBM scale for concurrent validity, subjects were asked three questions regarding perceptions of how severe the diabetes (HSD), previous metabolic control (PMC), and future metabolic control (FMC). HSD was rated by a three-point scale consisting of the categories of severe, average, or mild. PMC and FMC were rated on a four-point scale (well-controlled to uncontrolled). Items were scored so that high scores represented perceptions of severe diabetes, poor current control, and good future control. To examine the HBM scale for predictive validity, subjects completed a 26-item Diabetes Self-Care (DSC) scale. 12 The DSC was developed to be a self-report measure of the con>te11ation of aelf-care activities carried out in the home setting b~ individuals who require insulin. ReliabllitN by internal consistency for subjects in the follow-up component of the test phase was considered adequate (scale total alpha .89). The DSC scale contains three subscales that were alau internally consistent in this study: general (6 items, alpha=.80, N=124), diet (7 items, alpha = .81. N = 105), and insulin (9 items, alpha=.90, N =65). Two exercise and two foot care itemB make up the remainder of the DSC scale total. =
The inpatient pilot teat was conducted to field test the procedures that would be used m the prospective stud~ and to obtain additional reliability estimates of the HBM16. Data were collected from inpatient subjects the day after they were admitted. Eighty-nine subjects participated. Data from both pilot tests were combined in order to examResults ine the factor structure of the HBM 16 scale and to provide a firm data base for revising the scale, if needed, before the Reliability Estimates Measurement reliability has to do prospective study. One hundred twenty-seven subjects’ par- w ith the accuracn with which the scale measures the phenomena it made operational. Tests of internal consistency (Cronticipated m the pilot tests. The third phase of the data collection was the prospective hach’v alpha) and stability (Pearson correlation) are the study consisting of an mpaticnt and follow-up phase. Sub- traditional methods used to obtain reliability estimates of a jects completed the HBM scale (the HBM 12, a revision of the scale. The paired t-test was also done to examine the stability HBM 16 that will be discussed in the reliahility estimates sec- of the scald means from test to retest. tion) the day after thc) had been adiilitted. For the follow-up phase, the self-care scale was mailed to subjects’’ hollles 3 Pilot Tests Analyses of the HBM 16 revealed that two items weeks after discharge. Of the 196 subjects who had com- had very low discriminating power and that two others had pleted the HBM 12, 142 completed the fÓllow-up component negative item-to-related-item correlations. The four were considered for removal. Those 12 items formed a scale that approximately 5 weeks later. Downloaded from tde.sagepub.com at UNIV OF MASSACHUSETTS on March 16, 2015
47
had better
rellability estimates than those of the
Table ? ). The
HBM 16 (aee
of both the HBM 12 and HBM 16 were unchanged from the test to the retest. Examination of the factor structure of the HBMI2 (N 127) by a principal component analysis and varimax rotation provided another index of reliability. Eleven of the 12 items loaded cleanly (greater than .50 on one factor with a greater than .20 difference between that and its loading on another factor) on four conceptual]B rneanin‘~ful factors that represented the major dimensions of the HBM. The four factors accounted for 62 % of the scale variance. The first factor had an eigenvalue of 3.2, which computed to a theta coefficient of .75, a less conservative estimate of reliabiliy than the coefficient alpha. 13 The factor structure of the HBM 12 provided support for the reliability of the shorter scale. Therefore, the HBM12 was used for the prospective study. niean;
Prn.cp~rtim~ Stnclv The previously described factor procedue was used to provide the reliability estimate of the HBM 12 (N = 142) used in the prospective study. Eleven of the 12 items loaded cleanly on three factors that accounted for 51.4% of the scaleB variance. The first factor elgemalue of 2.6 computed to a theta coefficient of .68. The item that did not meet the criteria for factor loading was removed from the scale. The HBM was used to respond to the validity issues that follow. The mean score of subjects tor the H BM I scale total was somewhat above the midpoint of three (M=3.6, SD=0.43, N = 142). The range was 2.18 to 4.64.
Rotating the factors of a scale to the theory that theB represent is a method for determining construct Baltoity. The HBM II loaded onto three factors identified by Given, Given. Gallm, and CondonIl’ as being the conceptual dimensions of the HBM. These factors are low barrier, high benefit, and seriousness. Table 3 reports which of the 12 clusters that items had been 11) pothesized to represent in the original &dquo;calc, III thc belief that items Construct Validitv dxnenston
m
the
selected to represent in the Becker and lanl scale,&dquo; and the factor on which they loaded in this study. Factor loadings are displayed in Table 4. were
Criterion-Related Vahdity Estimates of criterion validity are proB ided by the relationships between scale scores and external variables. Data to examine the concurrent validity of during the mpamnt component of the prospective study. Data tll cBammc them predicts w as administered thc HBM I were obtained when the ,calc e BalidiU of the HBM scale Downloaded from tde.sagepub.com at UNIV OF MASSACHUSETTS on March 16, 2015
48
obtained approximately 34 days later during the followup component of the prospective study. were
Validity Estliiiates The three factors of the HBM11-low barrier (BAR), high benefit (BEN), and seriousness (SER)-were compared with subjects’ perceptions of their diabetes. The HBM I1 would have concurrent validity if the factors were logically associated with perceptions of diabetes severity and metabolic control. The use of subject Coiicut-i-eizt
as criterion-related variables was validated by the association detected between perception of previous metabolic control and glycosylated hemoglobin level. The correlation (r= +.17) between poor previous metabolic control (PMC) and the metabolic marker of diabetes control (HbA,) was interpreted to mean accuracy of subjects’
information circulars. These properties are the as it were, the papers that potential consumers use to make their judgments about the scale. The reliability and validity questions posed in this study were answered favorably. The HBM 11 is recommended for use to assess the diabetes health beliefs of individuals who use insulin. The HBM 11 provides a shorter alternative than the original HBM76 to determine the psychological readiness of individuals to self-manage their diabetes.
product scale’s
pedigree
perceptions
perceptions. Data from 134 subjects in the prospective study were entered into the correlation matrix. Although the relative associations were small, the direction of the relationships were all correct. The low barrier factor was negatively related to poor preand positively vious metabolic control (r=-.23, P
The Health Belief Model: Evaluation of a Diabetes Scale ANN C. HURLEY, RN, DNSc Edith Nourse Rogers Memorial Veterans Hospital
Bedford, Massachusetts
Scales that make theoretical
concepts of
health beliefs operational must be shown to have acceptable levels of reliability and validity before they can be incorporated into teaching programs. This paper describes the process used to evaluate a Health Belief Model scale. A revised 11-item scale is proposed for use by diabetes educators. Content validity of the initial scale (76 items) and the shorter version was verified. Reliability estimates obtained by factor structure provided evidence of measurement accuracy for the proposed 11-item scale. Analyses of construct and criterion validity provided additional support to suggest the use of the HBM11 scale for clinical practice.
Fundamental beliefs are strong motivators of human behavior. One strategy to promote self-care success with managing the diabetes regimen is for clinicians to devise an educational plan based on these beliefs. An accurate link must exist between the theoretical belief, which is abstract, and the world of practice, which is concrete. The belief must be made operational and expressed in objective terms before it can be applied to patient teaching. Then an accurate assessment of individuals’ beliefs can be conducted to guide the educational intervention. A number of scales are available for assessing the beliefs of individuals who have diabetes, but the caution of &dquo;buyer beware&dquo; must be exercised. In some respects, selection of a scale for a practice setting can be like buying an outfit from a mail-order catalog. It might fit perfectly, need a few alterations, or sit unused in the back of the closet. The same scrutiny that one applies to product evaluation and the selection of diabetes equipment should be applied to selecting a scale for clinical practice. Questions such as: What should it do? What are its specifications ? How has it worked previously’? need to be answered. Norbeck’ has suggested that answers to these questions be included in reports that describe instrument development. Consumers should be given a complete report of the conceptual basis of the scale, how the instrument was constructed, and its psychometric properties. This paper evaluates a scale that operationalized the Health Belief Model for individuals who have diabetes. The evalua-
Dr Hurley is Nurse Researcher/Project Director, Geriatric Research Education and Clinical Center, Edith Nourse Rogers Memorial Veterans
Hospital. An earlier version of this paper was presented at the Fifth Phyllis J. Verhonic Nursing Research Course sponsored by the United States Army Nurse Corps, April 1988. This study was supported in part by an individual National Research Service Award (#5F31NR0593) from the National Center for Nursing Research, National Institutes of Health; a clinical research grant from Alpha Chi Chapter, Sigma Theta Tau International; scholarships from the Leroy E. Dettman Foundation and the Reserve Officers Association of the United States; and tuition assistance from the United States Army. Reprint requests to Ann C. Hurley, RN, DNSc, 61 Babcock Street, Apt
3-A, Brookline, MA 02146. Downloaded from tde.sagepub.com at UNIV OF MASSACHUSETTS on March 16, 2015
45
tion process was conducted by application of the Norbeck criteria’ to answer the following reliability and validity
questions. 1. Does the scale have content validity’? 2. Does the scale have adequate reliability estimates by internal consistency and retest stability? 3. Does the scale have construct validity according to its factor structure? 4. Does the scale have adequate criteria-related estimates of concurrent and predictive validity’?
the hypothesized clusters. Six final clusters were declared to be stable and reproducible, but the criterion validity of the HBM76 was not examined. Becker and Janz&dquo; suggested that a shorter version of the HBM76 scale be used, and they identified 16 items to represent the HBM. Four items were selected to stand for each dimension: perceived susceptibility, severity, benefit, and barrier. The Becker and Janz scale will be referred to as the HBM 16. Content
Related Literature Basis The Health Belief Model (HBM) is a framework for understanding individuals’ psychological readiness to take health actions. The social psychologists who developed the model had a phenomenological orientation, that is, perception of reality rather than reality itself determines what individuals will or will not (lo.2 An individual’s evaluation of the goal and conviction that a given action would achieve the goal constitute the conceptual framework
Conceptual
underlying the HBM. Personal beliefs of perceived susceptibility to and seriousof the health condition of note, and perceived benefits of action weighed against barriers to action are considered the major dimensions of the HBM. The combined action of the distinct beliefs of the HBM is an integral part of its theoretical foundation.33 Since the HBM is concerned with belief; that can be changed, the model has been used as a framework to guide many and diverse health behavior invesiigaiion;.4 outpatient pilot. (’’) an inpatient pilot, and (3) a prospective study that included an inpatient and follow-up component. The investigator recruited all potential subjects. The purpose, procedures, risks, and benefits were explained, and patients who agreed to participate provided written informed
Procedures
an
consent.
The outpatient pilot test was conducted to examrne the stability of the scale without creating a situation that might alter the very beliefs the scale made operational. To accurately test the stabilit) of the HBM 16, it was necessary to seek subjects who currently had stable diabetes, whose treatment plan had not recently changed, and for whom neither were expected to change in the near future. Those criteria were assumed to be present in outpatients who had been seen in the clinic within
the past 6 months and who were not scheduled for an rnpatient admission. For the test component, potential subjects were mailed a packet of materials consisting of the instructions, consent form, and the study iiiatei-lais. The 38 patients who had responded to the inmal mailing were sent the second packet of materials. Twenty-seven subjects’ participated in the retest phase. The mean duration between test and retest waa ??
days.
The HBM 16 incorporated a five-point Likert scale in which subjects selected a number from one to tive (strongly agree, agree, undecided, disagree, or strongl~ disagree) to indicate their belief in the statement. High scores equate with psychological readiness to undertake diabetes health actions. Strong agreement with positively worded items representing perceived susceptibility, seriousness, benefit, and low barriers was scored as tive. Negatively worded items were reverse scored.
Other Measures Diabetes information and demographic data were available in the medical record. Glycosylated hemoglobin (HbAr) levels were determined at the clinic visit or when subjects were admitted to the inpatient unit and were available in the medical record. HbA, was measured by use of the G1~ trac system (distributed by Corning Medical, Corning Glass Works). The nondiabetic range is 5.~‘’~ to 7.4% . To examine the HBM scale for concurrent validity, subjects were asked three questions regarding perceptions of how severe the diabetes (HSD), previous metabolic control (PMC), and future metabolic control (FMC). HSD was rated by a three-point scale consisting of the categories of severe, average, or mild. PMC and FMC were rated on a four-point scale (well-controlled to uncontrolled). Items were scored so that high scores represented perceptions of severe diabetes, poor current control, and good future control. To examine the HBM scale for predictive validity, subjects completed a 26-item Diabetes Self-Care (DSC) scale. 12 The DSC was developed to be a self-report measure of the con>te11ation of aelf-care activities carried out in the home setting b~ individuals who require insulin. ReliabllitN by internal consistency for subjects in the follow-up component of the test phase was considered adequate (scale total alpha .89). The DSC scale contains three subscales that were alau internally consistent in this study: general (6 items, alpha=.80, N=124), diet (7 items, alpha = .81. N = 105), and insulin (9 items, alpha=.90, N =65). Two exercise and two foot care itemB make up the remainder of the DSC scale total. =
The inpatient pilot teat was conducted to field test the procedures that would be used m the prospective stud~ and to obtain additional reliability estimates of the HBM16. Data were collected from inpatient subjects the day after they were admitted. Eighty-nine subjects participated. Data from both pilot tests were combined in order to examResults ine the factor structure of the HBM 16 scale and to provide a firm data base for revising the scale, if needed, before the Reliability Estimates Measurement reliability has to do prospective study. One hundred twenty-seven subjects’ par- w ith the accuracn with which the scale measures the phenomena it made operational. Tests of internal consistency (Cronticipated m the pilot tests. The third phase of the data collection was the prospective hach’v alpha) and stability (Pearson correlation) are the study consisting of an mpaticnt and follow-up phase. Sub- traditional methods used to obtain reliability estimates of a jects completed the HBM scale (the HBM 12, a revision of the scale. The paired t-test was also done to examine the stability HBM 16 that will be discussed in the reliahility estimates sec- of the scald means from test to retest. tion) the day after thc) had been adiilitted. For the follow-up phase, the self-care scale was mailed to subjects’’ hollles 3 Pilot Tests Analyses of the HBM 16 revealed that two items weeks after discharge. Of the 196 subjects who had com- had very low discriminating power and that two others had pleted the HBM 12, 142 completed the fÓllow-up component negative item-to-related-item correlations. The four were considered for removal. Those 12 items formed a scale that approximately 5 weeks later. Downloaded from tde.sagepub.com at UNIV OF MASSACHUSETTS on March 16, 2015
47
had better
rellability estimates than those of the
Table ? ). The
HBM 16 (aee
of both the HBM 12 and HBM 16 were unchanged from the test to the retest. Examination of the factor structure of the HBMI2 (N 127) by a principal component analysis and varimax rotation provided another index of reliability. Eleven of the 12 items loaded cleanly (greater than .50 on one factor with a greater than .20 difference between that and its loading on another factor) on four conceptual]B rneanin‘~ful factors that represented the major dimensions of the HBM. The four factors accounted for 62 % of the scale variance. The first factor had an eigenvalue of 3.2, which computed to a theta coefficient of .75, a less conservative estimate of reliabiliy than the coefficient alpha. 13 The factor structure of the HBM 12 provided support for the reliability of the shorter scale. Therefore, the HBM12 was used for the prospective study. niean;
Prn.cp~rtim~ Stnclv The previously described factor procedue was used to provide the reliability estimate of the HBM 12 (N = 142) used in the prospective study. Eleven of the 12 items loaded cleanly on three factors that accounted for 51.4% of the scaleB variance. The first factor elgemalue of 2.6 computed to a theta coefficient of .68. The item that did not meet the criteria for factor loading was removed from the scale. The HBM was used to respond to the validity issues that follow. The mean score of subjects tor the H BM I scale total was somewhat above the midpoint of three (M=3.6, SD=0.43, N = 142). The range was 2.18 to 4.64.
Rotating the factors of a scale to the theory that theB represent is a method for determining construct Baltoity. The HBM II loaded onto three factors identified by Given, Given. Gallm, and CondonIl’ as being the conceptual dimensions of the HBM. These factors are low barrier, high benefit, and seriousness. Table 3 reports which of the 12 clusters that items had been 11) pothesized to represent in the original &dquo;calc, III thc belief that items Construct Validitv dxnenston
m
the
selected to represent in the Becker and lanl scale,&dquo; and the factor on which they loaded in this study. Factor loadings are displayed in Table 4. were
Criterion-Related Vahdity Estimates of criterion validity are proB ided by the relationships between scale scores and external variables. Data to examine the concurrent validity of during the mpamnt component of the prospective study. Data tll cBammc them predicts w as administered thc HBM I were obtained when the ,calc e BalidiU of the HBM scale Downloaded from tde.sagepub.com at UNIV OF MASSACHUSETTS on March 16, 2015
48
obtained approximately 34 days later during the followup component of the prospective study. were
Validity Estliiiates The three factors of the HBM11-low barrier (BAR), high benefit (BEN), and seriousness (SER)-were compared with subjects’ perceptions of their diabetes. The HBM I1 would have concurrent validity if the factors were logically associated with perceptions of diabetes severity and metabolic control. The use of subject Coiicut-i-eizt
as criterion-related variables was validated by the association detected between perception of previous metabolic control and glycosylated hemoglobin level. The correlation (r= +.17) between poor previous metabolic control (PMC) and the metabolic marker of diabetes control (HbA,) was interpreted to mean accuracy of subjects’
information circulars. These properties are the as it were, the papers that potential consumers use to make their judgments about the scale. The reliability and validity questions posed in this study were answered favorably. The HBM 11 is recommended for use to assess the diabetes health beliefs of individuals who use insulin. The HBM 11 provides a shorter alternative than the original HBM76 to determine the psychological readiness of individuals to self-manage their diabetes.
product scale’s
pedigree
perceptions
perceptions. Data from 134 subjects in the prospective study were entered into the correlation matrix. Although the relative associations were small, the direction of the relationships were all correct. The low barrier factor was negatively related to poor preand positively vious metabolic control (r=-.23, P
