Assignment: One-Way Experimental Designs

Correlational research, which you explored in this week's Discussion, is useful in identifying relations between two variables, but does not make assumptions regarding cause and effect among the variables because researchers did not control for outside factors. To demonstrate possible causal relations among variables, researchers will need to manipulate variables in an experimental research design.

The variable that the researcher manipulates in an experimental research design is termed the independent variable. As a researcher, one important determination you need to make is the number of independent variables involved in the study. If you manipulate one independent variable, the study would be termed a one-way experimental design.

Researchers also need to determine dependent variables. In an experimental design, the dependent variable is the measure of the effect of the independent variable. If the dependent measure reveals an effect made by an independent variable, a researcher may be able to determine cause.

Consider a study that hypothesizes that 8-year-olds who play educational computer games score higher on intelligence tests than those who do not play educational computer games. Consider how many aspects you would need to address if you were conducting the study. First, you would need to understand that the independent variable is the game-playing, whereas the dependent variable is the scores on the intelligence test.

Next, you would need to determine the levels of the independent variable. In this scenario, suppose there are three levels of play: no play, some play (4 hours a week), and frequent play (8 or more hours a week).

Additionally, you would need to determine whether the study is a between-participants design or a within-participants design (also known as a repeated-measures design). A between-participants design uses different groups for each level. A within-participants design uses the same group, and that one group repeats the experiment for each level.

In this Assignment you apply key concepts related to experimental design to a research study and analyze and interpret the outcome.

Read the following study scenario:

Researchers are interested in the effectiveness of a particular treatment for insomnia. They contact 50 insomnia sufferers who responded to a newspaper advertisement to participate in the study. Each participant is given a pill with instructions to take it before going to sleep that night. The pill actually contains milk powder (a placebo). The participants are randomly assigned to receive one of two sets of instructions about the pill. One half of the participants are told that the pill will make them feel "sleepy," and the other half are told that the pill will make them feel "awake and alert." The next day the participants return to the lab and are asked to indicate how long it took them to fall asleep after taking the pill. The individuals who were told that the pill would make them feel sleepy reported that they fell asleep faster than the participants who were told the pill would make them feel alert.

Think about the concepts you read about this week about one-way experimental designs and analysis of variance (ANOVA), and how they apply to the above study.

The Assignment (1-2 pages):

With the study scenario in mind, complete the following:

1. Identify the independent variable and dependent variable. Indicate the number of levels in the independent variable and describe each level.

2. Indicate whether the research used a between-participants or a within-participants research design and how you determined this to be the case.

3. Presume a third condition was added to the study. In this condition, the participants are not given any information about the effects of the (placebo) pill. Next, suppose an analysis of variance (ANOVA) was conducted. Briefly interpret, in your own words, what it would mean if the F was significant as applied to this study.