MODEL-BASED ESTIMATION OF THE EXCESS FRACTION (ATTRIBUTABLE FRACTION)- DAY-CARE AND MIDDLE-EAR INFECTION

The methods of adjustment for estimation of the excess fraction (EF), or attributable fraction, based on conventional and dynamic (or regres sive or autoregressive) logistic regression modelling in a cohort stud y for a disease with recurrent episodes are considered. Throughout the paper, the computation of estimates with corresponding confidence int ervals is illustrated in a cohort study associating the incidence of a cute middle ear infection (acute otitis media) with type of day care i n northern Finland. The incidences of at least one episode and at leas t three episodes as well as the total number of episodes during the fi rst two years of life are considered. In our example, the estimates ob tained from the dynamic model appear to have smaller standard errors s ince the dynamic model effectively utilizes the time-dependency of the covariates.