How good is fine-grained Timeline Follow-back data? Comparing 30-day TLFB and repeated 7-day TLFB alcohol consumption reports on the person and daily level.

OBJECTIVE: This study examined the correspondence of two types of Timeline Follow-back (TLFB) methods, a web-based self-administered, repeated 7-day TLFB and an interviewer-administered 30-day TLFB of alcohol consumption.
METHOD: Participants were first- and second-year college students (n=323, 58.5% female). Day-to-day correspondence of drinking reports and correspondence of person-level indicators of drinking were assessed.
RESULTS: Results indicated that correspondence between the TLFB-30 and TLFB-7 reports was generally good for summary indicators of drinking, but TLFB-7 data indicated a statistically significantly higher number of total drinks consumed, a higher number of days drinking 4+/5+ drinks per day, and a lower number of abstinent days than TLFB-30. Similarly, day-to-day comparison of drinking reports showed that drinking days were more frequently reported using the TLFB-7, a trend which was more pronounced for distal weekdays than recent weekdays. Correlations between TLFB-7 and TLFB-30 reports of drinks per drinking day were also lower for distal compared to recent weekdays (r=0.61 vs. r=0.76). Using a Poisson regression model, a linearly increasing trend in the absolute value of the difference between TLFB-7 and TLFB-30 drinking reports per day as length of recall increases was found (b=0.013, z=4.43, with p<0.001).
CONCLUSIONS: Our results indicate that participants reported more drinking on the repeated TLFB-7 than on the standard TLFB-30. Furthermore, the result of daily level analyses showed that discrepancies between the methods increased as the length of recall increased. These findings suggest that TLFB assessments covering longer intervals may have reduced accuracy on a fine-grained scale.