When considering the effectiveness of occupational health services (OHS), it is best to think of it as a specific package of interventions. Whether the OHS is effective or not then depends on the availability of effective interventions. By intervention we mean purposefully induced changes in the work environment, in worker behaviour or in a (patho)-physiological function. The effectiveness of interventions results from evaluation by means of controlled experimental studies and by systematic reviews that pull together all these studies and synthesise their results.
The solution for bridging the apparent gulf between scientific evidence and occupational health practice is to employ the PICO acronym. The letters spell out the problem identified in OHS thus: p=Participants, I=Intervention(s), C=Control and O=Outcome(s). For example, is it possible to reduce noise exposure (O) by giving instruction on how to use ear plugs (I) to workers (P) compared to using the devices without the instruction (C)?
Based on a recently updated Cochrane review, the answer is that there is moderate-quality evidence that with instructions for insertion, the attenuation of noise by earplugs is 8.59 dB better (95% CI: 6.92 dB to 10.25 dB) compared to no instruction (2 RCTs, 140 participants). Similarly, we know that one cannot prevent back pain by teaching workers to use a supposedly correct lifting technique. We also know that many OHS do not provide ear plug instruction but do provide correct lifting instructions. For hearing loss and back pain outcomes we know these OHS interventions are not effective.
The use of Cochrane systematic reviews can thus help to show effectiveness of OHS. There are currently more than 140 reviews that are pertinent to occupational health. For each one, the scientific abstract and plain language summary are freely available to everybody everywhere.