Poststratification as a suitable approach to generalize findings of two cross-sectional studies along the Bavarian compulsory school entrance examination: An exemplary poststratified analysis for asthma, hay fever and wheezing.

BACKGROUND: A compulsory school entrance examination of pre-school children (SEU) is administered in the German state of Bavaria. Every second year since 2004, the examinations are expanded in six study regions using a cross-sectional survey design (GME). However, the extent to which the results of the GME surveys are generalizable to the SEU population is unknown. Therefore, this study carried out a poststratification of two different GME surveys. The aim was to observe the impact of poststratification on an exemplary analysis of influencing factors for three allergy and asthma related outcomes (hay fever, asthma, wheezing) and thus to better understand this important question.

METHODS: First, poststratification was applied to correct for deviances of the GME sample in comparison to the SEU population. Logistic regression was used to determine the auxiliary variables for the poststratification. Following this, a composite variable as a linear combination was created to calculate weighting factors. Next, logistic regression analyses were applied to analyze possible influencing factors for three allergy and asthma related outcomes (hay fever, asthma and wheezing) in two GME surveys (2005/2006 and 2012/2013). Subsequently, the differences arising from poststratification were examined in more detail.

RESULTS: This study supports the hypothesis that the GME sample deviates from the SEU population. Mother tongue other than German of at least one parent, complete vaccination status and conspicuous visuomotor test results were positively associated with participation in both GME surveys. The prevalence for hay fever, asthma and frequent wheeze did not change statistically significant from 2005/2006 to 2012/2013. In the twelve analyses before and after poststratification, male sex was statistically significant associated with the three allergy and asthma related outcomes (e.g. asthma 2005/2006 after poststratification, aOR: 2.06, 95%-CI: 1.56-2.71). A high body mass index was positively associated with asthma (e.g. 2005/2006 after poststratification, aOR: 1.12, 95%-CI: 1.05-1.20). Poststratification caused a significant change in the sample composition.

CONCLUSIONS: It might be suggested that a poststratification should be performed for each GME survey. Poststratification tended to make results more comparable with previous research. In accordance with previous research, this study confirmed that male sex and high BMI are associated with asthma.