*3.1. Study Characteristics and Response Rates*

Six construction companies operating in the Boston metropolitan area, Massachusetts, were invited to participate, and five agreed. Within each of these companies two worksites per company were randomly assigned to the intervention or the control, resulting in a total of 10 worksites. The participation rates for the follow-up surveys (of those who completed the baseline surveys) were 69% (*n* = 228/332) for FU1 and 78% (*n* = 118/151) for FU2, and were included in the analyses (Figure 2). At baseline, it was difficult to determine the total number of eligible workers on site and hence response rates of those eligible. We were able to record the number of workers at the site orientations and were able to capture almost all of the new workers that came on to the site after the orientation.

There were no significant differences between the intervention and control sites at baseline (Table 1), FU1 or FU2 for age, sex, race/ethnicity or education at any data collection interval. There were no significant differences (*p* ≥ 0.05) for those who completed surveys at baseline and those who did not at FU1 or FU2, with respect to age, sex, ethnicity/race, education level or job title.


**Table 1.** Distribution of demographic characteristics at baseline (*N* = 607).


**Table 1.** *Cont.*

AA = African American, H.S. = High School, G.E.D. = General Equivalency Diploma; SD = Standard Deviation.

**Figure 2.** Participant flow through the trial.

#### *3.2. Outcomes*

Similar to demographic characteristics, all the outcome variables were not statistically different between the workers in the intervention and control groups at baseline, except for physical demanding work (*p* < 0.001) (Table 2). However, as described in Section 2.10, models testing the hypotheses examined changes from baseline in the cohort accounting for baseline measurements.



FU1Follow-upFollow-up groups *p* number of workers who had pain or injury, at follow-up intervals this was measured as new pain or injury since baseline; 3 Physical demanding work was categorized as those nominating a 4 or 5 on the physically demanding scale.
