Question 1: Is there any evidence that mean BMI differs between women who had caesareans and women who did not?
BMI is a continuous variable and we have large samples so we can do a large sample Normal z test. In SPSS we do an independent samples t test and use the unequal variances row in the output.
This gives a difference in mean BMI, No minus Yes, equal to −1.04 Kg/m2, 95% confidence interval = −2.81 to −0.87 Kg/m2, P < 0.001.
Looking at this the other way round, the mean BMI for women who had caesareans exceeds that for women who did not have caesareans by 1.04 Kg/m2, 95% confidence interval = 0.87 to 2.81 Kg/m2. The difference was highly significant, so there is strong evidence that in this population women who have caesareans have higher mean BMI.
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Last updated: 21 february, 2012.
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