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Interrogative suggestibility: factor analysis of the Gudjonsson Suggestibility Scale (GSS 2)
Person. individ. DI# Vol. 13, No. 4, pp. 479481,
1992
Printed in Great Britain. All rights reserved
Copyright
$5.00 + 0.00 0191-8869/92 0 1992 Pergamon Press plc
Interrogative suggestibility: factor analysis of the Gudjonsson Suggestibility Scale (GSS 2) GISLI H. GUDJONSWN Institule of Psychiatry, De Crespigny Park, Denmark Hill, London SE58AF,
England
(Received 30 July 1991) Summary-The 20 “Yield” and 20 “Shift” items on the parallel form of the Gudjonsson Suggestibility Scale (GSS 2; Gudjonsson, 1987) were factor analysed for 129 Ss and rotated, using the Varimax procedure. As in the case of the original scale (GSS 1; Gudjonsson, 1984), the “Yield” and “Shift” items loaded on separate factors, supporting the view that at least two basic types of interrogative suggestibility exist. The internal consistency for the “Yield 1” , “Yield 2” and “Shift” subscales, were 0.87, 0.90 and 0.79, respectively.
INTRODUCTION Interrogative suggestibility is a special type of suggestibility which refers to the tendency of an individual’s account of events to be altered by misleading information and inter-personal pressure within interviews (Gudjonsson, 1984, 1987). In order to measure objectively interrogative suggestibility, Gudjonsson (1984) constructed a special scale, known as the Gudjonsson Suggestibility Scale (GSS I). Factor analysis showed the scale to consist of two independent factors, referred to as “Yield” and “Shift”. The former measures the tendency of the individual to yield to (mis)leading questions, whereas the latter refers to the extent to which the interrogator can alter (“Shift”) the S’s previous answers by interrogative pressure, which takes the form of negative feedback (i.e. criticizing the S’s previous answers). The internal consistency (alpha coefficients) of “Yield” and “Shift” were 0.77 and 0.69, respectively. The low internal consistency of “Shift” was subsequently improved by slightly modifying the scoring of the scale (Singh & Gudjonsson, 1987). The validity of the GSS 1 has been shown in a number of studies [see Gudjonsson (in press) for an extensive review]. Following the work carried out on the GSS 1, and a favourable external review by Grisso (1986), Gudjonsson (1987) constructed a parallel form, which became known as the GSS 2. Scores obtained on the GSS 1 and GSS 2 were found to correlate highly, even after a considerable time interval. The parallel form provided the opportunity for researching the test-retest reliability of suggestibility, both within and between testing sessions. In addition, as a clinical tool the two scales meant that patients could be tested on more than one occasion, which is a procedure recommended for forensic purposes (Gudjonsson, in press). The data so far published on the GSS 2 is far more limited than that on the GSS 1. In particular, unlike with the GSS 1 (Gudjonsson, 1984), the “Yield” and “Shift” parts of the GSS 2 were never factor analysed in order to see if the two parts of the scale were independent or related (Gudjonsson, 1987). On the GSS 1 “Yield” and “Shift” clearly loaded on separate factors, which is consistent with the theoretical background to the scale (Gudjonsson & Clark, 1986). Secondly, the internal consistency of the “Yield” and “Shift” parts of the scale remains unknown, although the scale is in common clinical use. The purpose of the present study was to remedy these deficiencies with the GSS 2. The two hypotheses formulated were as follows: (1) The “Yield” and “Shift” parts of the GSS 2, like those of the GSS 1, load on separate factors when factor analysed; and (2) “Yield” and “Shift” have satisfactory internal consistency. METHOD There were a total of 129 Ss in the study. One hundred were forensic male patients, with a mean age of 28 (SD = lo), and 29 were normal adult males, with a mean age of 26 (SD = 5). All Ss completed the parallel Gudjonsson Suggestibility Scale (GSS 2; Gudjonsson, 1987). The GSS 2 is identical to the GSS 1, except for the content of the narrative paragraph that makes up the scale and the leading questions asked about the story. The scale is presented to the S as a memory test, leaving the S unaware that his or her suggestibility is being monitored. The GSS 2 consists of a narrative paragraph that is read out to the S. It contains 40 distinct ideas that can be objectively scored for memory recall, with possible scores ranging from 0 to 40. After reading out the paragraph the examiner asks the S to tell all he or she can remember about the content of the paragraph. This makes up “immediate recall”. After about a 50 min delay, during which time unrelated tests may be administered, the S is again asked to report all he or she can remember about the paragraph. This gives “delayed recall”. Delayed recall is typically between 85 and 90% of immediate recall. After “delayed recall” is completed, the S is asked 20 specific questions about the content of the paragraph. Fifteen of the questions are (mis)leading, whereas five are not and are used as “buffer questions” (i.e. to disguise-the real purpose of the test). After asking the 20 questions the examiner tells the S that he or she has made a number of errors (“negative feedback”) and the 20 questions are repeated. The number of times that the S has changed his or her answers between the two trials is scored as “Shift”. As the interrogative part of the scale is made up of 20 questions the possible “Shift”
479
480
NOTES
AND
SHORTER
COMMUNICATIONS
scores range from 0 to 20. The number of times that the Ss yielded to the leading questions prior to the negative feedback is scored as “Yield 1” whereas the number of times he or she yielded after the negative feedback is scored as “Yield 2”. On each occasion the possible range of “Yield” score is between 0 and 15. “Yield 1” and “Shift” are typically added up and are referred to as “Total Suggestibility” (range of possible scores being &35). “Yield 2” is generally only used for additional clinical information. Since- “Shift” gives no indication about the direction in which the S’s answers have been altered as a result of the negative feedback, “Yield 2” gives an idea of whether the negative feedback made the S more or less susceptible to leading questions. Typically, Ss tend to yield more to the leading questions after the negative feedback has been administered, the difference generally being between one and two points.
RESULTS
The answers to the 20 questions (“Yield 1”) and the “Shift” scores to these questions following negative feedback were factor analysed and then rotated, using Varimax procedure. The statistical procedure used was identical to that used previously with the GSS 1 (Gudjonsson, 1984). The results are shown in Table 1. Table 1 shows that the “Yield 1” and “Shift” scores consistently load on separate factors. The 15 leading question items all load moderately high on Factor 1. Out of the five “buffer questions” (1, 5, 9, 13 and 17), only one (item 17) loaded modestly on Factor 1. It therefore makes sense both on theoretical and empirical grounds to exclude the “buffer questions” from the scoring of “Yield”. All the 20 “Shift” items load poorly on Factor 1, whereas with two exceptions (items 17 and 20) they load significantly on Factor 2. Overall, the respective loadings on the two factors, “Yield” and “Shift”, are generally somewhat higher than those found for the GSS 1. The internal consistency of the “Yield” and “Shift” items is quite impressive. The alpha coefficients were 0.87, 0.90 and 0.79, for “Yield l”, “Yield 2” and “Shift”, respectively. This is a marked improvement on the internal consistency of the GSS 1, where the alpha coefficients were quite modest (Gudjonsson, 1984). Table 2 gives the mean and standard deviation scores for the memory and suggestibility scores on the GSS 2. The scores are given separately for the 100 forensic patients and 29 normal Ss. t-Tests for independent samples show that the two groups differ significantly in their scores, with the forensic patients having inferior memory to the normal Ss and higher suggestibility scores. The scores for the forensic patients are very similar to those found on the GSS 1 for forensic referrals (Gudjonsson, 1990). Although “Yield” and ‘Shift” items loaded on separate factors, the two factors are significantly
Table 1. Factor
analysis (Varimax all item scores
Items
Factor
Yield 1: Item I Item 2 Item 3 Item 4 Item 5 Item 6 Item I Item 8 Item 9 Item 10 Item I1 Item 12 Item 13 Item 14 Item 15 Item 16 Item 17 Item 18 Item 19 Item 20
(0.03) 0.48 0.39 0.46 (0.15) 0.62 0.66 0.63 (0.04) 0.68 0.58 0.67 ( - 0.09) 0.61 0.62 0.66 (0.25) 0.46 0.65 0.51
1
rotation) Factor
of
2
(0.07) 0.29 0.06 0.09 (0.00) 0.26 0.11 0.00 (-0.05) 0.18 0. I5 0.03 (-0.09) 0.10 0.18 0.26 (-0.19) -0.01 0.12 0.10
Ship: Item Item Item Item Item Item Item Item Item Item Item Item Item Item Item Item Item Item Item Item
1 2 3 4 5 6 I 8 9 10 11 12 13 14 15 16 17 I8 19 20
0.00 0.34 0.30 0.08 0.16 0.17 0.16 0.08 - 0.03 0.20 -0.28 0.24 0.06 -0.02 0.06 0.25 0.24 0.00 0.21 0.06
0.43 0.42 0.29 0.56 0.38 0.54 0.38 0.37 0.52 0.57 0.31 0.55 0.34 0.35 0.50 0.50 0.05 0.69 0.53 0.10
Table 2. Mean and standard deviation scores for forensic referrals (N = 100) and normal Ss (N = 29) Forensic referrals
GSS 2 Memory 1 Memory 2 Yield 1 Yield 2 Shift TSS ‘P < 0.000.
Normal SS
Mean
SD
Mean
SD
I
10.8 9.2 6.4 7.8 4.2 10.6
7.1 6.9 4.2 4.7 3.6 6.5
22.8 20.7 3.7 4.6 2.1 5.8
10.8 7.0 3.1 4.4 2.0 5.2
-8.2’ -7.89 3.8’ 3.7’ 4.59 4.5.
NOTES
AND
SHORTER
COMMUNlCATlONS
481
correlated. The correlation with “Shift” is higher with “Yield 2” (r = 0.57, P < 0.001) than with “Yield 1” (r = 0.36, P < O.OOl),which is entirely consistent with the GSS 1 results (Gudjonsson, 1984).
The two hypotheses formulated in the introduction were supported. “Yield” and “Shift” do indeed load on separate factors, which supports the theoretical view of Gudjonsson and Clark (1986) that there are at least two basic types of interrogative suggestibility. The former is best construed as a tendency to yield to leading questions, whereas the latter is more an indication of how people cope with interrogative pressure (Gudjonsson, 1988). The high internal consistency of the GSS 2 items represents an improvement on the GSS 1 where the alpha coefficients were quite modest. The low internal consistency on the GSS 1 “Shift” factor (Gudjonsson, 1984) was particularly worrying and resulted in slight modification to the original scoring (Singh & Gudjonsson, 1987). Whether the superior internal consistency in the present study indicates that the GSS 2 is overall a more reliable measure than the GSS 1 remains to be seen. Of course, very high internal consistency (e.g. of about 0.90 or above) may not be desirable in that it suggests that some items may be redundant. This is unlikely to be a problem with the GSS 2 in the sense that factor analysis of the “Shift” and “Yield” items does not indicate excessively high loadings on the two factors. What can be concluded, on the basis of the present findings, is that the GSS 2 contains items that are internally consistent and load significantly, but not excessively so, on their respective “Yield” and “Shift” factor. This gives support for the potential clinical and research value of the GSS 2, which has been extensively documented in the case of the GSS 1 (Gudjonsson, in press). The present study indicates that GSS 2 has very similar mean and standard deviation scores to the GSS 1, which means that the two scales can be used interchangeably. REFERENCES
Grisso, T. (1986). Evaluating Cornpetencies: Forensic Assessments and Instruments. New York: Plenum Press. Gudjonsson, G. H. (1984). A new scale of interrogative suggestibility. Personality and Individual Dtfirences, 5, 303-314. Gudjonsson, G. H. (1987). A parallel form of the Gudjonsson Suggestibility Scale. British Journal of Clinical Psychology, 26, 215-221. Gudjonsson, G. H. (1988). Interrogative suggestibility: Its relationship with assertiveness, social-evaluative anxiety, state anxiety and method of coping. British Journal of Clinical Psychology, 27, 159-166. Gudjonsson, G. H. (1990). One hundred alleged false confession cases: Some normative data. British Journal of Clinical Psychology,
29, 249-250.
Gudjonsson, G. H. (in press). The Psychology of Interrogations, Confessions and Testimony. Chichester: John Wiley & Sons. Gudjonsson, G. H. & Clark, N. K. (1986). Suggestibility in Police Interrogation: A Social Psychological Model. Social Behaviour, 1, 83-104. Singh, K. & Gudjonsson, G. H. (1987). The internal consistency of the “shift” factor on the Gudjonsson Suggestibility Scale. Personality and Individual Differences, 8, 265-266.
1992
Printed in Great Britain. All rights reserved
Copyright
$5.00 + 0.00 0191-8869/92 0 1992 Pergamon Press plc
Interrogative suggestibility: factor analysis of the Gudjonsson Suggestibility Scale (GSS 2) GISLI H. GUDJONSWN Institule of Psychiatry, De Crespigny Park, Denmark Hill, London SE58AF,
England
(Received 30 July 1991) Summary-The 20 “Yield” and 20 “Shift” items on the parallel form of the Gudjonsson Suggestibility Scale (GSS 2; Gudjonsson, 1987) were factor analysed for 129 Ss and rotated, using the Varimax procedure. As in the case of the original scale (GSS 1; Gudjonsson, 1984), the “Yield” and “Shift” items loaded on separate factors, supporting the view that at least two basic types of interrogative suggestibility exist. The internal consistency for the “Yield 1” , “Yield 2” and “Shift” subscales, were 0.87, 0.90 and 0.79, respectively.
INTRODUCTION Interrogative suggestibility is a special type of suggestibility which refers to the tendency of an individual’s account of events to be altered by misleading information and inter-personal pressure within interviews (Gudjonsson, 1984, 1987). In order to measure objectively interrogative suggestibility, Gudjonsson (1984) constructed a special scale, known as the Gudjonsson Suggestibility Scale (GSS I). Factor analysis showed the scale to consist of two independent factors, referred to as “Yield” and “Shift”. The former measures the tendency of the individual to yield to (mis)leading questions, whereas the latter refers to the extent to which the interrogator can alter (“Shift”) the S’s previous answers by interrogative pressure, which takes the form of negative feedback (i.e. criticizing the S’s previous answers). The internal consistency (alpha coefficients) of “Yield” and “Shift” were 0.77 and 0.69, respectively. The low internal consistency of “Shift” was subsequently improved by slightly modifying the scoring of the scale (Singh & Gudjonsson, 1987). The validity of the GSS 1 has been shown in a number of studies [see Gudjonsson (in press) for an extensive review]. Following the work carried out on the GSS 1, and a favourable external review by Grisso (1986), Gudjonsson (1987) constructed a parallel form, which became known as the GSS 2. Scores obtained on the GSS 1 and GSS 2 were found to correlate highly, even after a considerable time interval. The parallel form provided the opportunity for researching the test-retest reliability of suggestibility, both within and between testing sessions. In addition, as a clinical tool the two scales meant that patients could be tested on more than one occasion, which is a procedure recommended for forensic purposes (Gudjonsson, in press). The data so far published on the GSS 2 is far more limited than that on the GSS 1. In particular, unlike with the GSS 1 (Gudjonsson, 1984), the “Yield” and “Shift” parts of the GSS 2 were never factor analysed in order to see if the two parts of the scale were independent or related (Gudjonsson, 1987). On the GSS 1 “Yield” and “Shift” clearly loaded on separate factors, which is consistent with the theoretical background to the scale (Gudjonsson & Clark, 1986). Secondly, the internal consistency of the “Yield” and “Shift” parts of the scale remains unknown, although the scale is in common clinical use. The purpose of the present study was to remedy these deficiencies with the GSS 2. The two hypotheses formulated were as follows: (1) The “Yield” and “Shift” parts of the GSS 2, like those of the GSS 1, load on separate factors when factor analysed; and (2) “Yield” and “Shift” have satisfactory internal consistency. METHOD There were a total of 129 Ss in the study. One hundred were forensic male patients, with a mean age of 28 (SD = lo), and 29 were normal adult males, with a mean age of 26 (SD = 5). All Ss completed the parallel Gudjonsson Suggestibility Scale (GSS 2; Gudjonsson, 1987). The GSS 2 is identical to the GSS 1, except for the content of the narrative paragraph that makes up the scale and the leading questions asked about the story. The scale is presented to the S as a memory test, leaving the S unaware that his or her suggestibility is being monitored. The GSS 2 consists of a narrative paragraph that is read out to the S. It contains 40 distinct ideas that can be objectively scored for memory recall, with possible scores ranging from 0 to 40. After reading out the paragraph the examiner asks the S to tell all he or she can remember about the content of the paragraph. This makes up “immediate recall”. After about a 50 min delay, during which time unrelated tests may be administered, the S is again asked to report all he or she can remember about the paragraph. This gives “delayed recall”. Delayed recall is typically between 85 and 90% of immediate recall. After “delayed recall” is completed, the S is asked 20 specific questions about the content of the paragraph. Fifteen of the questions are (mis)leading, whereas five are not and are used as “buffer questions” (i.e. to disguise-the real purpose of the test). After asking the 20 questions the examiner tells the S that he or she has made a number of errors (“negative feedback”) and the 20 questions are repeated. The number of times that the S has changed his or her answers between the two trials is scored as “Shift”. As the interrogative part of the scale is made up of 20 questions the possible “Shift”
479
480
NOTES
AND
SHORTER
COMMUNICATIONS
scores range from 0 to 20. The number of times that the Ss yielded to the leading questions prior to the negative feedback is scored as “Yield 1” whereas the number of times he or she yielded after the negative feedback is scored as “Yield 2”. On each occasion the possible range of “Yield” score is between 0 and 15. “Yield 1” and “Shift” are typically added up and are referred to as “Total Suggestibility” (range of possible scores being &35). “Yield 2” is generally only used for additional clinical information. Since- “Shift” gives no indication about the direction in which the S’s answers have been altered as a result of the negative feedback, “Yield 2” gives an idea of whether the negative feedback made the S more or less susceptible to leading questions. Typically, Ss tend to yield more to the leading questions after the negative feedback has been administered, the difference generally being between one and two points.
RESULTS
The answers to the 20 questions (“Yield 1”) and the “Shift” scores to these questions following negative feedback were factor analysed and then rotated, using Varimax procedure. The statistical procedure used was identical to that used previously with the GSS 1 (Gudjonsson, 1984). The results are shown in Table 1. Table 1 shows that the “Yield 1” and “Shift” scores consistently load on separate factors. The 15 leading question items all load moderately high on Factor 1. Out of the five “buffer questions” (1, 5, 9, 13 and 17), only one (item 17) loaded modestly on Factor 1. It therefore makes sense both on theoretical and empirical grounds to exclude the “buffer questions” from the scoring of “Yield”. All the 20 “Shift” items load poorly on Factor 1, whereas with two exceptions (items 17 and 20) they load significantly on Factor 2. Overall, the respective loadings on the two factors, “Yield” and “Shift”, are generally somewhat higher than those found for the GSS 1. The internal consistency of the “Yield” and “Shift” items is quite impressive. The alpha coefficients were 0.87, 0.90 and 0.79, for “Yield l”, “Yield 2” and “Shift”, respectively. This is a marked improvement on the internal consistency of the GSS 1, where the alpha coefficients were quite modest (Gudjonsson, 1984). Table 2 gives the mean and standard deviation scores for the memory and suggestibility scores on the GSS 2. The scores are given separately for the 100 forensic patients and 29 normal Ss. t-Tests for independent samples show that the two groups differ significantly in their scores, with the forensic patients having inferior memory to the normal Ss and higher suggestibility scores. The scores for the forensic patients are very similar to those found on the GSS 1 for forensic referrals (Gudjonsson, 1990). Although “Yield” and ‘Shift” items loaded on separate factors, the two factors are significantly
Table 1. Factor
analysis (Varimax all item scores
Items
Factor
Yield 1: Item I Item 2 Item 3 Item 4 Item 5 Item 6 Item I Item 8 Item 9 Item 10 Item I1 Item 12 Item 13 Item 14 Item 15 Item 16 Item 17 Item 18 Item 19 Item 20
(0.03) 0.48 0.39 0.46 (0.15) 0.62 0.66 0.63 (0.04) 0.68 0.58 0.67 ( - 0.09) 0.61 0.62 0.66 (0.25) 0.46 0.65 0.51
1
rotation) Factor
of
2
(0.07) 0.29 0.06 0.09 (0.00) 0.26 0.11 0.00 (-0.05) 0.18 0. I5 0.03 (-0.09) 0.10 0.18 0.26 (-0.19) -0.01 0.12 0.10
Ship: Item Item Item Item Item Item Item Item Item Item Item Item Item Item Item Item Item Item Item Item
1 2 3 4 5 6 I 8 9 10 11 12 13 14 15 16 17 I8 19 20
0.00 0.34 0.30 0.08 0.16 0.17 0.16 0.08 - 0.03 0.20 -0.28 0.24 0.06 -0.02 0.06 0.25 0.24 0.00 0.21 0.06
0.43 0.42 0.29 0.56 0.38 0.54 0.38 0.37 0.52 0.57 0.31 0.55 0.34 0.35 0.50 0.50 0.05 0.69 0.53 0.10
Table 2. Mean and standard deviation scores for forensic referrals (N = 100) and normal Ss (N = 29) Forensic referrals
GSS 2 Memory 1 Memory 2 Yield 1 Yield 2 Shift TSS ‘P < 0.000.
Normal SS
Mean
SD
Mean
SD
I
10.8 9.2 6.4 7.8 4.2 10.6
7.1 6.9 4.2 4.7 3.6 6.5
22.8 20.7 3.7 4.6 2.1 5.8
10.8 7.0 3.1 4.4 2.0 5.2
-8.2’ -7.89 3.8’ 3.7’ 4.59 4.5.
NOTES
AND
SHORTER
COMMUNlCATlONS
481
correlated. The correlation with “Shift” is higher with “Yield 2” (r = 0.57, P < 0.001) than with “Yield 1” (r = 0.36, P < O.OOl),which is entirely consistent with the GSS 1 results (Gudjonsson, 1984).
The two hypotheses formulated in the introduction were supported. “Yield” and “Shift” do indeed load on separate factors, which supports the theoretical view of Gudjonsson and Clark (1986) that there are at least two basic types of interrogative suggestibility. The former is best construed as a tendency to yield to leading questions, whereas the latter is more an indication of how people cope with interrogative pressure (Gudjonsson, 1988). The high internal consistency of the GSS 2 items represents an improvement on the GSS 1 where the alpha coefficients were quite modest. The low internal consistency on the GSS 1 “Shift” factor (Gudjonsson, 1984) was particularly worrying and resulted in slight modification to the original scoring (Singh & Gudjonsson, 1987). Whether the superior internal consistency in the present study indicates that the GSS 2 is overall a more reliable measure than the GSS 1 remains to be seen. Of course, very high internal consistency (e.g. of about 0.90 or above) may not be desirable in that it suggests that some items may be redundant. This is unlikely to be a problem with the GSS 2 in the sense that factor analysis of the “Shift” and “Yield” items does not indicate excessively high loadings on the two factors. What can be concluded, on the basis of the present findings, is that the GSS 2 contains items that are internally consistent and load significantly, but not excessively so, on their respective “Yield” and “Shift” factor. This gives support for the potential clinical and research value of the GSS 2, which has been extensively documented in the case of the GSS 1 (Gudjonsson, in press). The present study indicates that GSS 2 has very similar mean and standard deviation scores to the GSS 1, which means that the two scales can be used interchangeably. REFERENCES
Grisso, T. (1986). Evaluating Cornpetencies: Forensic Assessments and Instruments. New York: Plenum Press. Gudjonsson, G. H. (1984). A new scale of interrogative suggestibility. Personality and Individual Dtfirences, 5, 303-314. Gudjonsson, G. H. (1987). A parallel form of the Gudjonsson Suggestibility Scale. British Journal of Clinical Psychology, 26, 215-221. Gudjonsson, G. H. (1988). Interrogative suggestibility: Its relationship with assertiveness, social-evaluative anxiety, state anxiety and method of coping. British Journal of Clinical Psychology, 27, 159-166. Gudjonsson, G. H. (1990). One hundred alleged false confession cases: Some normative data. British Journal of Clinical Psychology,
29, 249-250.
Gudjonsson, G. H. (in press). The Psychology of Interrogations, Confessions and Testimony. Chichester: John Wiley & Sons. Gudjonsson, G. H. & Clark, N. K. (1986). Suggestibility in Police Interrogation: A Social Psychological Model. Social Behaviour, 1, 83-104. Singh, K. & Gudjonsson, G. H. (1987). The internal consistency of the “shift” factor on the Gudjonsson Suggestibility Scale. Personality and Individual Differences, 8, 265-266.