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check completion of each instrument and of each item within each instrument. Nonetheless some questionnaires had missing items and where no more than two items were missing a method of pro-rating, by calculating the mean for the remaining items, was used. On a very few occasions, whole questionnaires were missing and this occurrence was specified in the presentation of the data in the foregoing chapters. This highlights the need for constant vigilance during the process of data collection.
10.3 Reliability of the methods of data collection
In this section, the methods of data collection are described, further possible sources of bias and the reliability of the interview and the self-completion scales are discussed.
10.3.1 Self-report
Sources of bias in self-report were discussed in Chapter 4; the literature on the veracity of self-report in this client group was reviewed and it was concluded that, although this method is by no means completely reliable, there is some doubt that other methods are superior. The relative benefits of using the method of obtaining data by self- report overrode the benefits of other methods of data collection for the purpose of the present study. Two additional considerations were central, one being the resource available for the study and the other being the applicability of the method and findings. The latter consideration necessitated the use of measures which are appropriate for routine use in a busy NHS addiction clinic (Tober et al. 2000).
Questions of the reliability of self-report are relevant both in the use of self- completion instruments and in the interview method. Self-completion was the method of choice in the development of the LDQ for reasons of speed of obtaining the data and the finding that the data provided were satisfactorily accurate. The use of interview schedules for ratings of dependence, for example the Edinburgh Alcohol Dependence Scale (EADS) (Chick 1980a) against which the Short-form Alcohol Dependence Data (SADD) was validated, (Davidson and Raistrick 1986) was deemed to be excessively time consuming at twenty-five minutes for routine use. Additionally, though Chick (1980a) reported high inter-rater reliability for the use of the EADS, he also reported that “on some items inadequate information was elicited by the unpractised interviewer” (p.184) suggesting the need for continuing training, practice and monitoring of reliability.
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