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in the past week.
5.7.9 Reliability
Reliability of a scale may be measured in a number of ways and two were chosen in the present study. The internal consistency method was reported above in section 5.7.5 and found to be satisfactory; the test re-test reliability method is reported below. In order to examine the re-test reliability of the adapted Impaired Control Scale, the instrument was administered as part of a battery of questionnaires to a separate sample of 61 individuals attending the clinic at the Leeds Addiction Unit at different stages of their treatment for heroin dependence. Oppenheim (1992) has described problems of resistance and of a practice effect that may impede the process of administering the same scale in the same conditions which is the basic requirement for this test. For this reason the requirement of completing the scale twice in the space of a week was carefully explained at the outset and individuals expressing any reluctance were not included in the study. The possibility of a practice effect was thought to be minimised by a minimum gap of 48 hours between completion of the scale on the two occasions; additionally it was surmised that the fact that there were three scales in the battery decreased the likelihood of a practice effect.
The sample consisted of 40 males (65.6%) and 21 females (34.4%), their mean age was 25.7 (SD = 4.9) and a range of 17 to 37. The mean time between first and second scale completion was 5.3 days with a minimum of two days and a maximum of 14 days. The three parts of the scale were treated separately as described in the previous sections of this chapter. A significant correlation was found between the mean scores for each of the parts; the mean scores at the first and second time points were then compared in order to eliminate the possibility that the correlation was based upon change rather than constancy. No significant difference was found in the mean total score for each part of the scale between the first and second scale completion, indicating that the responses had remained constant. The results of these analyses are presented in Table 5.4.
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