A group of scientists wishes to investigate whether increasing the amount of folic acid in our diets can reduce blood pressure . A group of 25 Caucasian women , of ages 45-55 , is given a folic acid supplement ( 400mg ) for 16 months , while another group of 25 Caucasian women in the same age group is given a placebo ( a sugar pill ) . The resting systolic blood pressure for all subjects is measured at the beginning and end of the 16 weeks . Which of the following is a confounding variable for this experiment ? Gender Amount of folic acid consumed Age Diet