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Table 1 Average odds ratios and 95% confidence (CI) from the pooled analysis of genetic variants found to be associated with ADHD in more than one study (Faraone et al., 2005) [1]. Quantitative trait effects are estimated for these key findings using the variance components 2 relative risk calculator http://pngu.mgh.harvard.edu/~purcell/gpc/vc2rr.html. This program calculates the threshold, assuming a standard normal trait distribution, such that the QTL variance for the discrete category based upon this threshold would be the same as the QTL variance for the continuous measure. Assuming an additive genetic model, the proportion of phenotypic variance explained by the associated genes is around 3.2%. The number of families needed to replicate these findings with a nominal alpha of 0.05 and 80% is listed, in addition to the power from a sample of 200 families for the same significance level.

From: The IMAGE project: methodological issues for the molecular genetic analysis of ADHD

Gene OR 95% CI Allele frequency QTL Number of families to replicate with 80% power Power in sample of 200 cases and 200 controls
DRD4 1.16 1.03 1.31 0.12 0.001 3196 0.115
DRD5 1.24 1.12 1.65 0.35 0.004 728 0.341
DAT1 1.13 1.03 1.24 0.73 0.001 2748 0.125
DBH 1.33 1.11 1.59 0.5 0.007 391 0.561
SNAP-25 (T1065G) 1.19 1.03 1.38 0.5 0.003 1043 0.253
SERT (HTTLPR) 1.31 1.09 1.59 0.6 0.006 466 0.490
HTR1B 1.44 1.14 1.83 0.71 0.010 315 0.652