Use of relative and absolute effect measures in reporting health inequalities

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The distinction between relative and absolute effects is also relevant in the context of reporting health inequalities.In both etiologic and descriptive studies, the impact of characteristics such as social class, ethnic background, or geographic location on health outcomes may be quantified in relative or absolute terms. As with other exposures, the choice of effect measure in reporting health inequalities influences our understanding of secular trends and which populations may experience a higher disease burden. In some cases, absolute and relative measures may diverge with respect to the magnitude or direction of change of health inequalities, leading to fundamentally different study conclusions. Methodological overviews of measuring and monitoring health inequalities,including the World Health Organization’s Commission on Social Determinants of Health,thus recommend reporting both absolute and relative measures, whenever possible, for properly tracking health inequalities.

We examined 344 articles published during calendar year 2009 in ten leading medical and public health journals, to determine how often researchers report health inequalities using absolute and/or relative effect measures. We found that 40% (138/344) of articles reported an effect measure in the abstract; among these, 88% (122/138) reported only a relative measure, 9% (13/138) reported only an absolute measure, and 2% (3/138) reported both. 75% (258/344) of all articles reported only relative measures in the full text; corresponding absolute measures were incalculable in 46% (119/258) of these. 18% (61/344) of all articles reported only absolute measures in the full text, and 7% (25/355) reported both absolute and relative measures. These results were consistent across journals, exposures, and outcomes.