Quantifying and estimating additive measures of interaction from case-control data        
        
    
        Volume 4, Issue 2 (2017), pp. 109–125
            
    
                    Pub. online: 26 April 2017
                    
        Type: Research Article
            
                
             Open Access
Open Access
        
            
    
                Received
22 March 2017
                                    22 March 2017
                Revised
12 April 2017
                                    12 April 2017
                Accepted
12 April 2017
                                    12 April 2017
                Published
26 April 2017
                    26 April 2017
Abstract
In this paper we develop a general framework for quantifying how binary risk factors jointly influence a binary outcome. Our key result is an additive expansion of odds ratios as a sum of marginal effects and interaction terms of varying order. These odds ratio expansions are used for estimating the excess odds ratio, attributable proportion and synergy index for a case-control dataset by means of maximum likelihood from a logistic regression model. The confidence intervals associated with these estimates of joint effects and interaction of risk factors rely on the delta method. Our methodology is illustrated with a large Nordic meta dataset for multiple sclerosis. It combines four studies, with a total of 6265 cases and 8401 controls. It has three risk factors (smoking and two genetic factors) and a number of other confounding variables.
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