A researcher is examining the relationship between color preferences and gender. A sample of 30 men and 30 women is obtained, and each person is asked to identify his/her preference between two choices of paint colors for a new student lounge. For this sample, 5 of the men preferred color A, and 15 of the women preferred color A. If a chi-square test is used to evaluate the relationship, what is the df value for the chi-square statistic?