Chunk #7 — Materials and Methods — Data summarization and dimension reduction

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Genome-wide association study of d-amphetamine response in healthy volunteers identifies putative associations, including cadherin 13 (CDH13).

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First we imputed missing phenotype values using probabilistic principal components analysis [37], [38] with five principal components, using the R [39] package ppca [40]. This approach exploits correlations among phenotypes to impute missing values. In the final dataset 98.74% of phenotype values were observed and 1.26% were imputed.