Exercise: BMI, alcohol consumption, and sex in the 2005 questionnaire

In the exercise BMI and alcohol consumption in the 2005 questionnaire in Week 9, we saw that BMI was sigificantly positively related to alcohol consumption. The regression equation was

        BMI = 23.9 + 0.074 × alcohol per week

The 95% confidence interval for the slope was 0.008 to 0.141 Kg/m² per unit of alcohol per week and the P value = 0.028.

In that exercise, we commented that there may be other variables involved in this relationship, such as sex. In this exercise we look at the influence of sex on BMI.

The following figure shows the relationship between BMI, alcohol consumption, and sex:

Question 1: What do you think the relationship is, based on this graph?

Check suggested answer 1.

The multiple regression equation is:

        BMI = 21.3 + 0.057 × alcohol consumption + 1.93 × sex

where sex = 1 for a female and sex = 2 for a male.

Question 2. How would you interpret this regression equation?

Check suggested answer 2.

The confidence intervals and P values for the coefficients are:

Term in equation	Coefficient	95% CI	P
alcohol	0.057	-0.009 to 0.122	0.09
gender	1.93	0.76 to 3.10	0.001
intercept	21.3	19.5 to 23.0	<0.001

Question 3: How would you assess the evidence concerning alcohol consumption and sex as predictors of BMI?

Check suggested answer 3.

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Last updated: 8 December, 2006.

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