Participants and procedures
University students in Costa Rica (longitudinal analytic sample, N = 242), around half of them from health-related disciplines (56 %), took part in an educational experiment. Mean age was 21 years (SD = 3.9 years). Most participants were women (61 %), single (97 %), and the majority perceived their health as being good or excellent (78 %).
A sample of 440 students participated at baseline, and 307 of them took part at Time 2 (307 completers, 133 non-completers). Non-completers cited academic duties (field work, meetings) as reasons for drop out. The highest rate of missing values corresponds to Time 2 (T2) behaviour (10.4 %). Due to mismatch, the remaining analytic sample was of n = 242 participants.
To avoid spill-over between conditions, classroom groups were randomized to determine whether students received the experimental condition or the control condition. Class lists, provided by the university, were used by researchers to randomise classroom groups (as control variables). Participants remained blind to their allocation during the study. The experiment and data collection were performed between March and November 2014. Participants were recruited over this period of time, and questionnaires were filled out in their classrooms. The questionnaires were completed at baseline and six weeks later.
The study procedures were approved by the ethics committee of the Universidad de Costa Rica. Informed consent was provided by all participants before receiving the baseline questionnaires.
Experimental and control conditions
Information on how to clean their hands (rubbing palms, back of hands, under fingernails, between fingers) as well as when and in which situations it is needed (before meals and before going to bed, after using the toilet, coughing or sneezing, touching animals, going to public places, after and before travelling, as well as whenever the hands get dirty) was included in an experimental pamphlet.
A planning task was presented, in which participants had to elaborate, based on their everyday life activities, three action plans on how often, when, where, and how to clean their hands (e. g., “after meeting my classmates in the library on Wednesday, by applying my hand sanitizer…). They also had to specify coping plans, in concrete, what to do to implement their plans in case difficulties appear (e.g., "in case I forget my hand sanitizer, I can buy one in the shop in front of the library after meeting my classmates").
Participants in the experimental condition received, read and filled out the health education pamphlet just after completing the baseline questionnaire. Research assistants were available to supervise the planning task, and to answer questions concerning the intervention and the questionnaire completion.
In the control condition, participants only completed the baseline questionnaire, without any further information pamphlet or task.
The study variables were hand hygiene behaviour (use of hand sanitizer), coping planning, and action control, measured at baseline (Time 1; T1) and six weeks later (Time 2; T2). Hand hygiene was measured by the item: “During the past week, I disinfected my hands with hand sanitizer”. Responses followed a 5-point Likert scale, including “0–2”, “3–4”, “5–6”, “7–9”, and “10 or more”, indicating the daily frequency of using disinfectant within one week.
Social-cognitive variables had a 4-point Likert scale response format. Coping planning was measured with three items, such as “To keep my habit in difficult situations, I made a concrete plan for disinfecting my hands, considering what to do when I am in a hurry”. Cronbach’s alpha was .82 at T1 and .88 at T2. Action control was measured with three items, such as “During the week, I watched consistently when, how often, and how to disinfect my hands”. Cronbach’s alpha was .78 at T1 and .81 at T2.
Change scores for the social-cognitive variables were computed by subtracting T1 scores from T2 scores.
Statistical analyses were performed with SPSS 22. Drop-out analyses were performed by means of t-tests for continuous variables and χ2 for categorical variables, in order to compare the retained and lost individuals at T2. Randomization checks were conducted between participants of the control and the experimental conditions. MANOVA was used to test the baseline differences for continuous variables, and χ2 tests were used for categorical variables. Intervention effects were examined by means of repeated measures ANOVA. Psychological mechanisms were assessed in terms of serial mediation with the SPSS PROCESS macro by Hayes . In serial mediations multiple mediators are assumed to operate sequentially in a causal chain, from an independent variable, through more than one mediator, and concluding in a final consequent variable. In the present case changes in action control and changes in coping planning, in this order, were specified as sequential mediators between the intervention and T2 hand hygiene behaviour. To control for classroom effects, classroom was specified as a control variable using the fixed effects approach (see e.g., Cohen et al., 2003, pp. 539–544). In this approach the control variables are dummy coded to partial out their effects in the model. Gender and baseline behaviour were included as covariates.