The resulting paternal blocking structure can be used for phasing and imputation of sire genotypes.
At 24 months, an intention to treat analysis using all 667 participants recruited, and imputation of BMI for the 170 lost to follow-up and the 14 missing values, showed that mean BMI was significantly lower in the intervention group (16.53) than the control group (16.82), with a difference of 0.29 (95% confidence interval 0.02 to 0.55, P=0.04) (table 2).
All available data from the 28 d intervention period were used, and no imputation of missing data was performed.
The large sample size and number of events, and the use of multiple imputation of missing values, controls for both random and systematic error, and thus enables accurate estimation of associations although ideally there would be no missing values.
Furthermore, our study demonstrates the use of imputation of untyped genotypes as a powerful means of exploiting existing GWAS data sets to identify low-frequency disease-causing variants.
One way to solve this particular issue may be to use multiple imputation of utility values, rather than a single imputation as performed here.
To mitigate against loss of power resulting from reduced sample size and investigate possible bias related to missing data, we used multiple imputation of exposures and covariates using the ice function in Stata version 12 using the missing-at-random assumption 15, 17.
Changes from baseline were analyzed using ANCOVA with region and treatment as factors, and baseline as covariate (using LOCF imputation of missing data).
Daily measurements of sulfur dioxide and nitrogen oxides were conducted year-round and were used in the imputation of PM2.5 and PAHs for nonsampled days.
Statistical and social network analysis will be used to characterise and describe the results, using multiple imputation of missing data prior to analysis [ 55, 81].
