1 Finnish Foundation for Alcohol Studies, P. O. Box 220, FIN-00531 Helsinki,
2 Department of Mental Health and Alcohol Research, National Public Health Institute, Mannerheimintie 166, FIN-00300 Helsinki,
3 Medical School, University of Tampere, P. O. Box 719, 33101 Tampere and
4 Research Unit of Substance Abuse Medicine, University of Helsinki, Finland
Received 11 February 2002; in revised form 28 March 2002; accepted 1 May 2002
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ABSTRACT |
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INTRODUCTION |
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Traditional quantityfrequency questionnaires (QF) focus on typical, or habitual, intake. No options are provided to report more infrequent drinking occasions and less typical amounts. Hence, both frequent intake of small amounts and infrequent intake of high amounts remain underreported. Another problem is the lack of information on the total amount of alcohol consumed during one drinking day (except if all subjects under study were to drink only beer, or only wine, or only spirits). A partial solution to these difficulties is to ask separately about the frequency of heavy drinking days in addition to the questions that map out average alcohol intake. A logical extension of this latter approach is to inquire separately into the frequency of drinking days for various quantity levels of alcohol intake, say one to two drinks, three to four drinks, etc. The latter series of questions are now known as graduated frequency questionnaires (GF). Recent World Health Organization (2000) guidelines consider GF to be the method of choice.
GF seems to yield higher estimates of alcohol intake than QF. Data from the 1979 US National Alcohol Survey showed that GF produced 38% higher alcohol intake estimates than QF. This was partly due to a longer recall period (1 year vs 1 month) as well as to better reporting of heavy drinking occasions (Room, 1991). In a representative sample of nearly 4000 adults in Ontario, Canada, prevalence of harmful drinking was virtually three times higher for GF than for QF (Rehm et al., 1999
). However, GFs have not been much used in research, and little is known about their accuracy (Greenfield, 2000
; Leigh, 2000
). As Rehm et al. (1999)
pointed out, GF methods yield at present only indirect support in terms of reliability and validity. In the present study, we have compared GF and QF with a 1-month daily alcohol intake diary. A daily diary was used as the gold standard as, at least in motivated volunteers, the literature over many years has tended to consider this as the most accurate way to collect data on alcohol intake from subjects living in their natural community settings.
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SUBJECTS AND METHODS |
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Alcohol intake
Average alcohol intake was estimated both before (time 1) and after the daily diary period (time 2) by applying two self-report instruments: a quantityfrequency questionnaire (QF1 and QF2 respectively) and a graduated frequency questionnaire (GF1 and GF2 respectively).
QF presented 10 drinking frequency options (never, 12 times per year, 34 times per year, approximately every second month, approximately once a month, approximately twice a month, once a week, 23 times a week, 45 times a week, 67 times a week), and nine quantity options for beer (including cider and pre-mixed cocktails), wine and spirits. The highest quantity option was open-ended (5 or more litres of beer, 1.5 l or more of wine, 1 l or more of spirits). Examples of questions are as follows: how often did you consume spirits during the past 12 months?; how much spirits did you usually consume during the days when you drank spirits?
GF allowed for eight number of drink levels (from 15 or more drinks per day to 12 drinks per day). A drink was defined as a standard serving in a restaurant or bar with an alcohol content of 12 g each. Detailed instructions were issued to calculate the number of drinks in various glass sizes and bottle volumes for beer, wine and spirits. The subject then chose one of seven drinking frequency levels (never, not more than 3 times a month, approximately once a week, 23 times a week, 45 times a week, 6 times a week, practically every day) for each relevant number of drink level. QF1 and GF1 were administered immediately before the beginning of the diary-keeping period; QF2 and GF2 were returned within a week after the end of the diary-keeping period. Record-keeping lasted 31 consecutive days. The subjects were instructed not to deviate in any way from their earlier drinking patterns.
Blood tests
A fasting venous blood sample was drawn after the QF1 and GF1 and serum was prepared and stored at 20°C until assayed. Axis-Shield immunoassay for quantitative measurement of carbohydrate-deficient transferrin (CDT) was used and CDT is reported here as %CDT in proportion to the total transferrin (Axis-Shield Asa, Oslo, Norway). Serum aspartate aminotransferase (ASAT), alanine aminotransferase (ALAT) and -glutamyltransferase (GGT) were determined using established clinical chemical methods (Johnson & Johnson, Clinical Diagnostics, Rochester, NY, USA). These values are reported in units per litre (U/l).
Data
Of the 52 volunteers, seven did not complete GF1, the daily diary or give a blood sample. An additional seven failed to complete one or more items in QF1. Fourteen cases produced inadequate data in QF2 and eight in GF2. Complete alcohol intake data were available for 34 subjects (28 females). One of the cases in this group reported very low alcohol intake in both QF and GF and no intake in daily diary. Incomplete data were observed for 18 subjects (15 females). Significant (P < 0.05) differences were not found between the cases with and without complete alcohol data in terms of sex, age (mean: 44 vs 40 years), quantityfrequency estimate at time 1 (13 vs 11 g/day), graduated frequency estimate at time 1 (31 vs 22 g/day), ASAT (22 vs 25 U/l), ALAT (28 vs 31 U/l), GGT (29 vs 26 U/l) or CDT (4.2 vs 3.8 %). The 2-test was applied for categorical data and a t-test for continuous data.
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RESULTS |
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When the daily diary estimate and the quantityfrequency and graduated frequency of alcohol intake, both before (1) and after (2) the daily record-keeping period, were compared, all estimates showed clear linear associations in scatterplots. There were no obvious outliers. All correlations between the five estimates were high (Table 2). Comparison between time 1 and time 2 showed that the testretest reliability of both QF and GF was good.
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DISCUSSION |
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In theory, a daily diary kept by motivated volunteers is the best available way to collect comprehensive and accurate data on the many dimensions of alcohol intake from subjects living in their natural community settings. However, much depends on the motivation and conscientiousness of the volunteers. We offered laboratory tests free of charge before the diary period in the hope that it would increase motivation, both because the tests might be seen as a small compensation for participation and also because some participants might think that the tests are a way to check the truthfulness of responses to questions. This did not seem to be a total success, however, since 35% of the volunteers did not complete the diary period. Perhaps they were more motivated to have free tests than by altruistic reasons. As we have no way to check the accuracy of the responses by the study completers, the possibility remains that their responses did not fully meet the gold standard accuracy. However, credibility to the latter is lent by the finding that all alcohol questionnaire measures showed close correlation with GGT, an objective blood test known to associate with alcohol intake (Poikolainen et al., 1985), and slightly less close correlations with ASAT and ALAT. The poor correlation between alcohol intake and CDT might be at least partly related to the observation that this association is weaker among women than men (Allen et al., 2000
), as most of our subjects were women.
To explore the possible causes of overestimation by GF, daily diary intake was compared with GF1 intake. The rationale of this choice was that diary-keeping could not have influenced GF1, since it was filled in before the start of the daily diary. The fact that GF1 and GF2 correlated closely and yielded similar mean and SD values suggests that record-keeping did not influence the responses to the later GF2. The former as well as the close similarity of QF1 and QF2 responses points to the conscientiousness and precision of the study subjects in reporting their alcohol intake.
GF yielded clearly higher alcohol intake estimates than the diary. This might be due to (a) underestimation of actual intake by diary or (b) overestimation of GF intake. Weekday variation might bias the diary intake figures downwards if it was considerable and low intake days were under-represented in the data. According to the diaries, our subjects consumed more on Fridays, Saturdays and Sundays than during the rest of the week. However, all subjects reported on four weekends except one whose diary included five weekends. Moreover, most of the 31-day diary periods included the May Day, a traditional revelling festival in Finland. Therefore, it is unlikely that diary intake was underestimated. Overestimation is more probable.
Some overestimation may also occur, if the actual number of drinks consumed is closer to the lower class limit than the category average (the latter is assumed in calculations). In our GF, an odd number of drinks was always the lower and an even number the higher option within a response category. Of all drinking days, 56% yielded an odd number of drinks. Thus, deviations from the category averages had little influence on the overestimation in the present data.
GF is a family of questionnaires and versions with many drink level categories may inflate the magnitude of intake estimates. Our GF contained as many as eight drink level categories. Earlier thinking aloud analyses on similar GF versions suggest that some heavy drinkers, having much to report to the high quantity level items in the beginning of GF, may feel obliged to find something to report also at lower levels. Some may reinterpret the questions, for example thinking that to have only one to two drinks means at least one to two drinks (Greenfield, 2000). Because of these problems, GF versions with five drink level categories have been used recently.
A study on 83 volunteers from the San Francisco Bay area found that the average recalled past 30-day alcohol intake measured by graduated frequency mailed questionnaire was 96% of the respective intake measured by weekly retrospective diaries (Hilton, 1989). The respective proportion by past 14-day quantityfrequency mail questionnaire was 95%. The intake estimates by all three methods were closely correlated. Good agreement between the various methods might be related to four factors. First, the GF had only five drink level categories. Secondly, the sample consisted of relatively heavily drinking young adults. Thirdly, the daily diary data came from the retrospective recall of drinking during the past 7 days and, fourthly, mail questionnaires were answered after the 10-week daily diary period. In contrast to this, larger underreporting has been found in a study in which the questionnaire was answered before the daily diary period (Poikolainen and Kärkkäinen, 1983
).
In conclusion, the results suggest that, when the respondents are motivated to recall their alcohol intake, both QF and GF classify individuals in the correct rank order according to their actual alcohol intake. GF data seem to overestimate markedly actual alcohol consumption, whereas QF data slightly underestimate it.
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ACKNOWLEDGEMENTS |
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FOOTNOTES |
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REFERENCES |
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