Distal Measurements Can Produce False Negative Results: A Prospective Secondary Analysis of a Natural History Study.

introductionMost prospective studies of quit attempts (QAs) or abstinence measure the ability of variables to predict quitting many weeks or months later. This design ignores more proximal fluctuations in the predictor that may be more relevant. The present secondary analysis compares 6-week (distal) and daily (proximal) changes in cigarettes per day (CPD) as predictors of making a QA.

methodsDaily smokers reported CPD and QAs nightly throughout a 12-week natural history study. We provided no treatment. In the distal analysis, we tested whether reduction in CPD between baseline and 6 weeks predicted making a QA during the following 6 weeks. In the proximal analysis, we identified episodes of one or more days of ≥10% reduction in CPD and tested whether reduction predicted making a QA on the day immediately after the reduction episode. We tested the following predictors: (1) reduction in CPD of ≥10% (yes/no), (2) percent reduction, (3) absolute magnitude of reduction, and (4) CPD at the end of reduction.

resultsIn the distal analysis, reduction did not predict making a QA. In the proximal analysis, any reduction (OR = 3.0), greater percent reduction (OR = 1.6), greater absolute reduction (OR = 1.3), and fewer CPD on the final day of an episode (OR = 11.8) predicted making a QA the next day (all p < .001). DISCUSSION: Relying on distal measurements to identify causes of a behavior may produce false-negative results. Increased use of technological advances will make assessments of the more valid proximal measurements more feasible. IMPLICATIONS: This secondary analysis tested distal and proximal predictors of making a quit attempt among the same participants and found that distal tests did not, but proximal tests did predict quit attempts. Relying on distal measurements may result in false negatives.