3. More types of variables and data Independent and Dependent Variables Many statistical experiments explore relationships between variables. In some cases, one variable (known as independent) predicts another variable (known as dependent). In some cases, several independent variables predict a single dependent variable. In graphical terms, Independent variables are plotted on the X-axis while dependent variables are on the Y-axis. Relationships Between Variables If two variables are distributed consistently, we conclude that a relationship exists. However, you must be careful how you characterize this relationship. Are the variables merely correlated, or is there a causal relationship (that is, one variable causes the other)? Check Your Understanding Identify whether each of the following variables is a nominal, ordinal, discrete, or continuous variable. Variable of interest Eye color Qualitative Quantitative Nominal Ordinal Discrete Continuous Average speed driven Sale price of a car Number of cars sold Survey response (Strongly disagree, Disagree, Neutral, Agree, Strongly agree) Distance traveled Length of a phone call Annual Income 00 O Grade It Now Save & Continue