The distribution of birthweight of singletons in city ofTianjin, China is approximately normal with mean m=3,445 grams andstandard deviation = 409 grams [2]. An investigator plans toconduct a study to determine if birthweight for singletons whosemothers were with gestational diabetes mellitus (GDM) have the samemean. Based on literature search, the true mean birthweight forinfants whose mothers with GDM is estimated 3,800 grams (± 250grams). The investigator wants 90% power to detect the differences.A two-tails test conducted at the 0.05 level of significance willbe used. What sample size is needed for this study? if the power ischanged to 80%, what sample size is then needed?
