The meta-analysis searched for asthma susceptibility variants for which the same allele was associated with asthma in the different studies. For each study, we constructed a test statistic that has a standard normal distribution under the null hypothesis of no association and captures the direction of the effect (i.e., the statistic was positive if the reference allele was associated with an increased risk of asthma). The meta-analysis test statistic was calculated as a linear combination of the individual study scores with weights proportional to the square root of the number of cases (or trios). P-values were obtained using normal approximations. Odds ratios were calculated by combining linearly log odds ratios with weights reflecting the standard errors from the genome-wide association studies.
