Model selection(absolute humidity and relative humidity) and Akaike's information criterion(AIC): Association between humidity and asthma admission

Abstract

Background- There are published many studies of humidity effect on health condition. Humidity condition affects severity of asthma symptom. When studying association between humidity and health outcomes, we more use relative humidity than absolute humidity. We need to examine validity of humidity indicators. Aims-This study are to examine validity of using humidity indicator about association between humidity and health conditions Methods-We used the generalized additive model (GAM) to analyze data which is daily weather and asthma admission in Korea from 2003 to 2006 for humidity effect on asthma. Using asthma admission data of 6 cities, we analyzed to change humidity indicators absolute humidity and relative humidity respectively after controlling air pollution condition, temperature. Calculating moving average each of variables we controlled lag effect. Results-Among 6 cities, Seoul and Kwangju cities did not show significant results about humidity effect on asthma admission. In Busan and Incheon cities, AIC was calculated in the model with absolute humidity is lower 12176.87 (RR: 0.9398 95% CI : 0.9023-0.9788) , 9234.068 (RR :0.9064, 95% CI: 0.8468-0.9701) respectively than that of using relative humidity. On the other hand, Daegu and Daejeon is shown higher AIC in model with using absolute humidity that of relative humidity model. AIC of Daegu and Daejeon cities are 9064.49 (RR: 0.9577, 95% CI: 0.9381-0.9776), 7668.60 (RR: 0.9479, 95% CI: 0.9208-0.9759) in relative humidity model. Conclusions-This study did not show evidence to select which humidity indicator clearly. However Busan and Incheon Cities showed lower AIC in absolute humidity model whereas AIC of Daegu and Daejeon was lower in relative humidity model. Salient different of these cities is founded geographical position. Busan and Incheon city is closer coast. On the contrary, Daegu and Daejeon city is inland city.