Response Bias in the Nationwide Epidemiological Survey of an Intractable Disease In Japan

Annual numbers of patients with the so-called intractable diseases were estimated in the nationwide epidemiological surveys under the assumption that the mean number of patients among “responded” hospitals is equal to that among “non-responded” hospitals. This paper evaluated the validity of this assumption, using the data of Idiopathic thrombopenlc purpura (ITP) obtained from the nationwide epidemiological survey and the number of ITP patients who are financially subsidized for treatment (FST-patients). The mean numbers of ITP FST-patients among “responded” hospitals in the nationwide survey were compared with the mean numbers among “non-responded’ hospitals. The ratio of the mean number among “responded” hospitals to that among all hospitals was found to be between 1.0 and 1.1; suggesting that this assumption was sufficiently valid.