The seven - year study, involving 37,000 workers at 1,500 locations, is based on empirical data rather than on personal reports, which tend to be less accurate.
وهي تستند الى احصاءات بدلا من ان تكون مجرد تقارير شخصية ،‏ الامر الذي يجعلها اقل دقة .‏