Statistical Analyses Statistical analyzes revealed that in order to achieve a 90% power that allows researchers to detect a mean difference of 10% between the experimental and control groups, the sample needed to include between 1,052 and 4,058 participants. Therefore, researchers aimed to recruit at least 1,200 mothers. A = 0.05 two-sided test was used with equal numbers in each group. α Primary analyses were derived from known data whereas parallel sensitivity was obtained from multiple imputation, based on the method of chained equations. Imputed values were randomly sampled from the posterior predictive distribution of the missing data. In general, results from both, the known data and multiple imputation analyses were the same (Barr et al., 2009). The type of analysis for this study was selected independently from the study’s results. For continuous measures, a t-test was used to measure the mean difference between the experimental group, receiving the Period of PURPLE crying program, and the control group, receiving injury prevention material. The incidence of rate ratios for the number of diary events was estimated by using a negative binomial regression. Interactions of the variables of education, mode of learning the program (reading the booklet or watching the DVD), parity of infants, and inconsolable crying, was examined through the use of statistical tests of interactions along with main effect terms. If measures were not normally distributed, nonparametric comparisons were used to confirm significance (Barr et al., 2009). Findings There was missing data about age, education, and marital status for 3%, family income for 9%, and outcomes for knowledge and behavior for 4% of the sample. All four of the diary measures were missing for 17% of the participants. When comparing women who were missing
Statistical Analyses Statistical analyzes revealed that in order to achieve a 90% power that allows researchers to detect a mean difference of 10% between the experimental and control groups, the sample needed to include between 1,052 and 4,058 participants. Therefore, researchers aimed to recruit at least 1,200 mothers. A α = 0.05 two-sided test was used with equal numbers in each group. Primary analyses were derived from known data whereas parallel sensitivity was obtained from multiple imputation, based on the method of chained equations. Imputed values were randomly sampled from the posterior predictive distribution of the missing data. In general, results from both, the known data and multiple imputation analyses were the same (Barr et al., 2009). The type of analysis for this study was selected independently from the study’s results. For continuous measures, a t-test was used to measure the mean difference between the experimental group, receiving the Period of PURPLE crying program, and the control group, receiving injury prevention material. The incidence of rate ratios for the number of diary events was estimated by using a negative binomial regression. Interactions of the variables of education, mode of learning the program (reading the booklet or watching the DVD), parity of infants, and inconsolable crying, was examined through the use of statistical tests of interactions along with main effect terms. If measures were not normally distributed, nonparametric comparisons were used to confirm significance (Barr et al., 2009). Findings There was missing data about age, education, and marital status for 3%, family income for 9%, and outcomes for knowledge and behavior for 4% of the sample. All four of the diary measures were missing for 17% of the participants. When comparing women who were missing