ABSTRACT
An attribute independent variable is a characteristic or a “part” of the participants, whether or not the study takes place. It is not manipulated by the researcher. Some common attribute variables, such as ethnicity, gender, and IQ, are not easily changed. Other attributes, such as age, income, job title, personality traits, and attitudes, can change over time. The key characteristic of attribute independent variables is that they are measured, not manipulated. An active independent variable is manipulated or caused to vary systematically. The treatment or condition that the group receives may be determined by the experimenter or sometimes by someone else, often a group (school, clinic, etc.). The researcher or other person actively gives different groups different treatments, and the differences between groups that have different treatments are usually the focus of the study. The most common active variable is when an experimental and comparison group receive different treatments (curricula, interventions, etc). The participants might be randomly assigned to groups or already be in intact groups such as school classes. 1.3. What is the difference between the independent variable and the dependent variable? In the classic definition of the independent variable, it is the variable that is manipulated; however, in this book and commonly in the field, the term “independent variable” is used more broadly to mean the presumed cause of differences in the outcome variable. The scores or values for the dependent variable “depend on” the level of the independent variable. For example, you might have an experiment in which you are testing the effectiveness of a new weight reduction plan, say reduced carbohydrates. The independent variable involves whether or not the participant was on the low carbohydrate diet. One group (one level of the independent variable) is given and follows a low carbohydrate diet, whereas the other group (the other level of the independent variable) eats their normal diet. Then to determine if the low carbohydrate system works, the researcher might make weight measurements before the low carbohydrate diet is initiated and again following a certain period of time (during which one group was on the low carbohydrate diet and one was not). The weight measurements serve as the dependent variable. Thus, the researcher is hoping that the low carbohydrate treatment (the independent variable) affects a change in weight (the dependent variable). 1.5 Write a research question and a corresponding hypothesis regarding variables of interest to
you but not in the HSB data set. Is it an associational, difference, or descriptive question? Of course the answers to this question will vary greatly. An associational question will most likely involve the relation between two normally distributed variables, for example, “Is there an association between IQ scores and SAT scores for high school seniors?” Difference questions usually compare two to four groups on some outcome variable. For example, “Are there differences between three different weight loss programs in regard to the average weight loss?”
