Gue? guen and Jacob (2012) asked female restaurant wait staff to wear different colored T-shirts on different days for a six-week period and recorded the tips left by male customers. The results show that male customers gave significantly bigger tips when the wait persons were wearing red. What is the independent variable for this study? Number of male customers who left a tip Size of tip Day on which the wait person wore red Color of the T-shirt (red versus not red) What is the dependent variable for this study? Number of male customers who left a tip Size of tip Color of the T-shirt (red versus not red) Day on which the wait person wore red What scale of measurement is used for the independent variable? Ordinal Interval Ratio Nominal

The independent variable is: Color of the T-shirt (red versus not red) The dependent variable is: size of the tip Scale measurement for the independent variable: nominal

The study aimed to conclude whether or not, the color of the waitresses' clothes, influences the amount of money they were receiving as tips from male customers. Therefore, the independent variable is the color of the t-shirt, and the study tries to assess whether it produces a causal effect over the dependent one: the size of the tips.

The independent variable is measured in a nominal or qualitative form as the values recorded are not the result of counting, they refer instead to the names of different groups or categories to which the observations in the dataset are connected.