A Cochrane review 1 included two interrupted time-series studies conducted a) in the companies in USA and b) on federal injury data. In these studies two interventions of interest were evaluated: mandatory random drug testing and mandatory random and for-cause alcohol testing programmes.
In reanalysis of the data in one study mandatory random and for-cause alcohol testing was associated with a significant decrease in the level of injuries immediately following the intervention (-1.25 injuries/100 person years, 95% CI -2.29 to -0.21) but the intervention did not significantly affect the existing long-term downward trend (-0.28 injuries/100 person years/year, 95% CI -0.78 to 0.21).
Mandatory random drug testing was significantly associated with an immediate change in injury level following the intervention (1.26 injuries/100 person years, 95% CI 0.36 to 2.16) in one study, but in the second study there was no significant effect (-1.36/injuries/100 person years, 95% CI -1.69 to 0.41). In the long term, mandatory random drug testing was associated with a significant increase in the downward trend of injuries in one study (-0.19 injuries/100 person years/year, 95% CI -0.30 to -0.07) and in the downward trend in fatal accidents in another study (-0.83 fatal accidents/100 million vehicle miles/year, 95% CI -1.08 to -0.58).
Comment: High quality interrupted time-series is a feasible study design but a cluster-randomised trial would be the ideal one. The study was downgraded for quality and design (no control).
1. Cashman CM, Ruotsalainen JH, Greiner BA, Beirne PV, Verbeek JH. Alcohol and drug screening of occupational drivers for preventing injury. Cochrane Database Syst Rev 2009 Apr 15;(2):CD006566. [PMID:19370641]
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