RELIABILITY OF THE PARENTAL BONDING INSTRUMENT AND INTIMATE BOND MEASURE SCALES Kay Wilhelm and Gordon Parker
The long-term reliability of the Parental Bonding Instrument (PBI) and of the Intimate Bond Measure (IBM) are examined in a non-clinical group, with data being examined over eleven and five years for the two respective measures. Such reliability data are compared with reliability data on a number of personality measures within the same cohort. Results demonstrate considerable stability in the PBI over an extended period and moderate stability in IBM scores. Australian and New Zealand Journal of Psychiatry 1990; 24:199-202 The Parental Bonding Instrument (PBI) was developed to measure fundamental parental dimensions of care and protection (control) and to allow quantification of any parental contribution to subsequent psychiatric disorder. Reliability aspects (internal consistency and short-term test-retest reliability) were examined in the initial paper [ 11 and its validity, both as a measure of perceived and actual parenting, has been examined in several studies [ 2 ] . If the PBI is a reliable and valid measure of subjects’ retrospective memories of their parents in their first sixteen years, then adult subjects should return consistent scores over time (ie show high test-retest reliability). The short-term reliability of the PBI has been examined in several studies. In the initial development paper [ 11, test-retest reliability in a non-clinical sample was 0.76 for the care scale and 0.63 for the protection scale over a three-week interval. Subsequently, in a sample of depressives initially depressed and then
Division of Psychiatry, Prince Henry Hospital, Little Bay, NSW Kay Wilhelm, FRANZCP, Staff Psychiatrist Gordon Parker, MD, PhD, FRANZCP, Professor of Psychiatry Correspond with Dr Wilhelm
significantly improved, much higher correlation coefficients (ranging from 0.87 to 0.92) were returned over a nine-weekinterval [ 2 ] .The higher coefficients in this group, compared to the initial sample, were judged to reflect the greater motivation of patients (in comparison to volunteer or importuned non-clinical groups) to return questionnaire data conscientiously. Subsequently, in a US study [3] of depressed outpatients attending the Yale Depression Research unit, 48 depressives scored the PBI when depressed and some four-six weeks later when significantly improved. PBI scores showed no significant change over time and the coefficients of agreement ranged from 0.90 to 0.96 across the four scales, slightly superior to the Australian depressed sample. Test-retest reliability in a group of patients with schizophrenia has been examined [4] when the coefficients of agreement ranged from 0.58 to 0.77. This less impressive result was judged to be a reflection of the sample initially scoring the PBI shortly after admission to hospital with an exacerbation of their schizophrenia, with their judgement and ability to complete the self-report questionnaire impaired. This interpretation is supported by a n American study [5] of 26 subjects with schizophrenia who completed the PBI form on two occasions a few weeks apart, with correlation coeffi-
200
RELIABILITY OF THE PBI AND IBM SCALES
cients ranging from 0.79 to 0.88, with this sample being distinguished by the sample being selected from those attending a community mental health centre, and not assessed during a relapse. Medium-term reliability data have been provided [6], with correlation coefficients ranging from 0.79 to 0.81 on the PBI for a non-clinical U.S. sample tested seven months apart. In the only published study [7] of the long-term reliability of the PBI, women were studied in the post-partum period and then two to four years (mean 30 months) later. Only the maternal PBI form was completed by subjects, and the authors reported that PBI scores were “remarkably stable over time” for different sub-groups of mothers who were either depressed on both occasions of testing, initially depressed and then recovered, or not depressed on either occasion. In this paper we examine the test-retest reliability of the PBI over a decade. The sample has been described elsewhere [8] and so details only will be summarized here. In September 1978,380 students who had undertaken a basic Arts or Science university course, and who were then completing a one-year training programme at the Sydney Teachers’ College were approached in class and invited to participate in a longitudinal study. While our key objective was to examine for sex differences in depressive experience over time, the students were not informed about the specific hypothesis, but were given details on the range of topics (including depression) and developmental issues that would be assessed longitudinally. Those subjects completed PBI data and 170 agreed to take part in the longitudinal study, and so formed the study cohort, then having a mean age of 23.1 years. Those taking part and those declining did not differ in PBI scores returned for each parent. Subsequently, we sought to interview the cohort serially, and self-report data were obtained from 164 in 1983 and 163 in 1988. On each occasion the subjects were requested to complete the orthodox PBI forms (assessing parenting over the first 16 years), allowing us to compare PBI data collected over extended periods. The authors have also developed a measure of fundamental dimensions underlying adult intimate relationships [9]. The test-retest reliability of that selfreport, the Intimate Bond Measure (or IBM) was assessed in the initial paper, with a non-clinical sample returning data on two occasions over a three-six week interval, with reliability coefficients being very high at 0.80 and 0.89. That measure was given to our
present cohort in 1983 and in 1988 and we now report the test-retest reliability over a five-year interval. It must be kept in mind, however, that subjects would not necessarily be scoring the same “intimate” on both occasions, so that we report consistency data for the whole sample and for a sub-sample of those who were married in 1988 and had rated the same “intimate” in 1983 - a fairer test of the measure’s reliability. On each occasion, subjects were asked to score characteristics of the intimate “in recent times”, the IBM being more a measure of state or current characteristics. We also take the opportunity to report test-retest reliability over the same extended period for a number of other measures. We do that for several reasons. Firstly, such reports are rare and, more importantly, those data provide some basis for comparison against the PBI and IBM. It is generally suggested that personality is constant and we might therefore expect that high test-retest reliability would be demonstrated for personality measures and give a base quantitative estimate of reliability against which we could judge PBI data, in particular. That is, if personality is immutable, then self-report measures of personality should show a high level of constancy, being weakened only by response biases and state effects (eg depression) which are generally accepted to influence self-report scoring. Thus, we would expect that if the PBI is a reliable measure, reliability coefficients should be similar to those returned on personality measures. The personality measures considered were the Eysenck Personality Inventory neuroticism scale [ 101, the Rosenberg self-esteem scale, [ 111 the dependency scale from the Depressive Experiences Questionnaire [ 121, the Costello-Comrey trait depression scale [ 131 which was designed to measure a “person’s tendency to experience a depressive mood”, and the Bem sex role inventory [ 141 (with masculinity, femininity and social desirability sub-scales), the last being administered in 1983 and 1988 only. Finally, we report data on the Wilson-Lovibond state measure of depression [ 151 to again allow comparison against the “trait” measures, anticipating that much lower levels of agreement should be demonstrated on a state measure over time.
Results Table 1 reports the mean data returned for the several measures, and the level of constancy over time, with three intervals (1978-1983, 1983-1988, and
KAY WILHELM AND GORDON PARKER
Table I . Consistency in scores examined over time
Mean score
Consistency coefficients (r)
1978 1983 1988
A 0 A with with with
(A)
(6)
(C)
26.3 14.8 21.9 13.0
26.2 13.8 21.7 12.1
26.3 13.8 21.4 11.9
c
c
PBI Aaternal care inaternal protection ’aternal care 'sternal protection
0.72 0.82 0.6: 0.74 0.76 0.61 0.80 0.82 0.7; 0.69 0.67 0 5
BM ntimate care wholegroup) ntimate control wholegroup) ntirnate care sub-group)” ntimate control sub-group)
N/A* N/A N/A N/A
30.6 29.5 N/A 6.7
0.50 N/A
6.9 N/A
0.49 N/A
31.5 30.2 N/A
0.48 N/A
6.5
7.0 N/A
0.49 N/A
Personality qeuroticism Self-esteem’”* lependency rraitdepression
9.0 8.7 1.0 1.6 52.6 52.8 31.3 31.2
8.7 0.9 53.7 29.4
0.54 0.43 0.64 0.64
0.68 0.61 0.64 0.65
0.5 0.4 0.5 0.4
Statedepression
1988 (t = 0.87, ns). In a similar, but less distinct fashion, depression scores decreased from 1978 to 1988, both on the trait (t = 2.03, PcO.05) and state (t = 2.21, P
The long-term reliability of the Parental Bonding Instrument (PBI) and of the Intimate Bond Measure (IBM) are examined in a non-clinical group, with data being examined over eleven and five years for the two respective measures. Such reliability data are compared with reliability data on a number of personality measures within the same cohort. Results demonstrate considerable stability in the PBI over an extended period and moderate stability in IBM scores. Australian and New Zealand Journal of Psychiatry 1990; 24:199-202 The Parental Bonding Instrument (PBI) was developed to measure fundamental parental dimensions of care and protection (control) and to allow quantification of any parental contribution to subsequent psychiatric disorder. Reliability aspects (internal consistency and short-term test-retest reliability) were examined in the initial paper [ 11 and its validity, both as a measure of perceived and actual parenting, has been examined in several studies [ 2 ] . If the PBI is a reliable and valid measure of subjects’ retrospective memories of their parents in their first sixteen years, then adult subjects should return consistent scores over time (ie show high test-retest reliability). The short-term reliability of the PBI has been examined in several studies. In the initial development paper [ 11, test-retest reliability in a non-clinical sample was 0.76 for the care scale and 0.63 for the protection scale over a three-week interval. Subsequently, in a sample of depressives initially depressed and then
Division of Psychiatry, Prince Henry Hospital, Little Bay, NSW Kay Wilhelm, FRANZCP, Staff Psychiatrist Gordon Parker, MD, PhD, FRANZCP, Professor of Psychiatry Correspond with Dr Wilhelm
significantly improved, much higher correlation coefficients (ranging from 0.87 to 0.92) were returned over a nine-weekinterval [ 2 ] .The higher coefficients in this group, compared to the initial sample, were judged to reflect the greater motivation of patients (in comparison to volunteer or importuned non-clinical groups) to return questionnaire data conscientiously. Subsequently, in a US study [3] of depressed outpatients attending the Yale Depression Research unit, 48 depressives scored the PBI when depressed and some four-six weeks later when significantly improved. PBI scores showed no significant change over time and the coefficients of agreement ranged from 0.90 to 0.96 across the four scales, slightly superior to the Australian depressed sample. Test-retest reliability in a group of patients with schizophrenia has been examined [4] when the coefficients of agreement ranged from 0.58 to 0.77. This less impressive result was judged to be a reflection of the sample initially scoring the PBI shortly after admission to hospital with an exacerbation of their schizophrenia, with their judgement and ability to complete the self-report questionnaire impaired. This interpretation is supported by a n American study [5] of 26 subjects with schizophrenia who completed the PBI form on two occasions a few weeks apart, with correlation coeffi-
200
RELIABILITY OF THE PBI AND IBM SCALES
cients ranging from 0.79 to 0.88, with this sample being distinguished by the sample being selected from those attending a community mental health centre, and not assessed during a relapse. Medium-term reliability data have been provided [6], with correlation coefficients ranging from 0.79 to 0.81 on the PBI for a non-clinical U.S. sample tested seven months apart. In the only published study [7] of the long-term reliability of the PBI, women were studied in the post-partum period and then two to four years (mean 30 months) later. Only the maternal PBI form was completed by subjects, and the authors reported that PBI scores were “remarkably stable over time” for different sub-groups of mothers who were either depressed on both occasions of testing, initially depressed and then recovered, or not depressed on either occasion. In this paper we examine the test-retest reliability of the PBI over a decade. The sample has been described elsewhere [8] and so details only will be summarized here. In September 1978,380 students who had undertaken a basic Arts or Science university course, and who were then completing a one-year training programme at the Sydney Teachers’ College were approached in class and invited to participate in a longitudinal study. While our key objective was to examine for sex differences in depressive experience over time, the students were not informed about the specific hypothesis, but were given details on the range of topics (including depression) and developmental issues that would be assessed longitudinally. Those subjects completed PBI data and 170 agreed to take part in the longitudinal study, and so formed the study cohort, then having a mean age of 23.1 years. Those taking part and those declining did not differ in PBI scores returned for each parent. Subsequently, we sought to interview the cohort serially, and self-report data were obtained from 164 in 1983 and 163 in 1988. On each occasion the subjects were requested to complete the orthodox PBI forms (assessing parenting over the first 16 years), allowing us to compare PBI data collected over extended periods. The authors have also developed a measure of fundamental dimensions underlying adult intimate relationships [9]. The test-retest reliability of that selfreport, the Intimate Bond Measure (or IBM) was assessed in the initial paper, with a non-clinical sample returning data on two occasions over a three-six week interval, with reliability coefficients being very high at 0.80 and 0.89. That measure was given to our
present cohort in 1983 and in 1988 and we now report the test-retest reliability over a five-year interval. It must be kept in mind, however, that subjects would not necessarily be scoring the same “intimate” on both occasions, so that we report consistency data for the whole sample and for a sub-sample of those who were married in 1988 and had rated the same “intimate” in 1983 - a fairer test of the measure’s reliability. On each occasion, subjects were asked to score characteristics of the intimate “in recent times”, the IBM being more a measure of state or current characteristics. We also take the opportunity to report test-retest reliability over the same extended period for a number of other measures. We do that for several reasons. Firstly, such reports are rare and, more importantly, those data provide some basis for comparison against the PBI and IBM. It is generally suggested that personality is constant and we might therefore expect that high test-retest reliability would be demonstrated for personality measures and give a base quantitative estimate of reliability against which we could judge PBI data, in particular. That is, if personality is immutable, then self-report measures of personality should show a high level of constancy, being weakened only by response biases and state effects (eg depression) which are generally accepted to influence self-report scoring. Thus, we would expect that if the PBI is a reliable measure, reliability coefficients should be similar to those returned on personality measures. The personality measures considered were the Eysenck Personality Inventory neuroticism scale [ 101, the Rosenberg self-esteem scale, [ 111 the dependency scale from the Depressive Experiences Questionnaire [ 121, the Costello-Comrey trait depression scale [ 131 which was designed to measure a “person’s tendency to experience a depressive mood”, and the Bem sex role inventory [ 141 (with masculinity, femininity and social desirability sub-scales), the last being administered in 1983 and 1988 only. Finally, we report data on the Wilson-Lovibond state measure of depression [ 151 to again allow comparison against the “trait” measures, anticipating that much lower levels of agreement should be demonstrated on a state measure over time.
Results Table 1 reports the mean data returned for the several measures, and the level of constancy over time, with three intervals (1978-1983, 1983-1988, and
KAY WILHELM AND GORDON PARKER
Table I . Consistency in scores examined over time
Mean score
Consistency coefficients (r)
1978 1983 1988
A 0 A with with with
(A)
(6)
(C)
26.3 14.8 21.9 13.0
26.2 13.8 21.7 12.1
26.3 13.8 21.4 11.9
c
c
PBI Aaternal care inaternal protection ’aternal care 'sternal protection
0.72 0.82 0.6: 0.74 0.76 0.61 0.80 0.82 0.7; 0.69 0.67 0 5
BM ntimate care wholegroup) ntimate control wholegroup) ntirnate care sub-group)” ntimate control sub-group)
N/A* N/A N/A N/A
30.6 29.5 N/A 6.7
0.50 N/A
6.9 N/A
0.49 N/A
31.5 30.2 N/A
0.48 N/A
6.5
7.0 N/A
0.49 N/A
Personality qeuroticism Self-esteem’”* lependency rraitdepression
9.0 8.7 1.0 1.6 52.6 52.8 31.3 31.2
8.7 0.9 53.7 29.4
0.54 0.43 0.64 0.64
0.68 0.61 0.64 0.65
0.5 0.4 0.5 0.4
Statedepression
1988 (t = 0.87, ns). In a similar, but less distinct fashion, depression scores decreased from 1978 to 1988, both on the trait (t = 2.03, PcO.05) and state (t = 2.21, P
