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by the author. The rationale for asking about the heaviest drinking day is discussed by Raistrick et al. (1994) and is based upon a comparison of methods of obtaining accurate self-report data in problem drinking and drug using populations. These are discussed in Chapter 3. Current use of heroin was calculated on the basis of amount of money spent on heroin per day on the heaviest day in the past week. The rationale for asking about the heaviest day follows that for alcohol. Amount spent is the most consistent measure reported by users. The gram equivalent of amount spent was checked at several intervals throughout the data collection period and found to be stable. There is regional variation in the purity of street heroin and in the amount of heroin that constitutes a regular daily habit. Since the entire sample was drawn from one city and quantities checked across the city, it was agreed in consultation with clinical staff in daily contact with help seeking heroin dependent people, to use a calculation that £20.00 spent would yield .3 grams of heroin. Again all calculations for amounts of heroin used in grams were made by the author. Calculation of a daily amount on the basis of amount of money spent was kept separate from the estimation of number of days per week using. This is for reasons relevant to the main analysis where number of days per week using would be investigated as to its relevance to severity of dependence.
Questionnaires to be used both in the study and in routine clinical practice were duplicated and the study sample information stored separately. All data were entered into SPSS files by the author.
7.3 Follow-up
Two follow-up periods were planned, one at three months which was thought to be a time frame of sufficient duration for changes to occur in the main study measures. It is a relatively common follow-up period in this field of study, expected to pick up any treatment effect. The second data collection point was planned to be twelve months from recruitment to the study in order further to determine the course and nature of changes where change occurred.
7.3.1 Follow-up measures
The five self-completion questionnaires were repeated at both the three month and the twelve month data collection points. The brief structured interview was shortened by taking out the items referring to age, sex, life time duration of use and of problem use. Remaining were the questions about main substance, use during the past week, attempts at abstinence and duration abstinence if successful. The reason for repeating the question about main substance was that the
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