Effects of booster interventions on factory workers' use of hearing protection

The provision of reinforcements or boosters to interventions is seen as a logical approach to enhancing or maintaining desired behavior. Empirical studies, however, have not confirmed the effectiveness of boosters nor assessed the optimum number of boosters or the timing for their delivery.

This randomized controlled trial contrasted the effect of four booster conditions (a). 30 days; (b). 90 days; (c). 30 and at 90 days; and (d). no boosters of the intervention to increase the use of hearing protection devices (HPDs).

A total of 1325 factory workers completed a computerized questionnaire and were randomly assigned to one of three computer-based (tailored, nontailored predictor-based, or control) multimedia interventions designed to increase the use of hearing protection devices. After the intervention, colorful boosters specific to the type of training received were mailed to workers' homes. Posttest measures of use were administered at the time of their next annual audiogram 6 to 18 months after the intervention. RESULTS Repeated measures of analysis of variance (ANOVA) showed a significant main effect for the booster (after 30 days) in the group that received tailored training (F[3442] = 2.722; p =.04). However, in the assessment of the interaction between time (pretest and posttest) and boosters (four groups), the ANOVA did not find significant differences in hearing protection device use for any of the training groups. To assess for significant differences between groups, post hoc comparisons were conducted at the pretest and posttest for the total sample and for the subsample of workers who reported using hearing protection devices less than 100% of the time needed. Sheffé contrasts by intervention group, gender, ethnicity, and hearing ability found no significant changes in the mean use of hearing protection devices for the booster groups.

Although the provision of boosters represented a considerable commitment of resources, their use was not effective in this study. However, it would be premature to eliminate boosters of interventions. Further study is needed to explore the effects of different booster types for increasing the use of hearing protection devices, and to assess carefully the effects of boosters on other health behaviors in studies with controlled designs.