Independent Variables and Dependent Variables

In empirical studies of psychology, it is essential to observe and understand variables and their measurements.  In statistics, the concept of a variable is dichotomized in terms of independent and dependent variables.  According to Howell (2013), independent variables (IV) are what scientists study, control, or manipulate as the cause or predictor of the dependent variable.  A dependent variable (DV) is what to be observed and measured to see how its values change as the condition or value of the IV changes.  In a research, "the study is about the independent variables, and the results of the study (the data) are the dependent variables" (Howell, 2013, p. 4).  For example, in an experiment a researcher often “examines relationships between variables by manipulating an independent variable to create different treatment conditions and then measuring a dependent variable to obtain a group of scores in each condition” (Gravetter & Wallnau, 2013, p. 30).  According to Gravetter and Wallnau (2013), the research variables are characterized by the type of values that can be assigned to them.  A discrete variable consists of separate, indivisible categories; a continuous variable is divisible into an infinite number of fractional parts.  In this study Schmidt (1994) specified the independent variable, humor, with two categories, humorous sentences and non-humorous sentences. 
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