Question

There are three (3) methods to control extraneous variables that have become potential confounds. Choose any TWO (2) of these, and DESCRIBE how each method works to control extraneous variables. Answer this question using the following format:

1. IDENTIFY the method and DESCRIBE how it controls extraneous variables.

2. IDENTIFY the method and DESCRIBE how it controls extraneous variables

Answer 1

Extraneous variables are unwanted factors in a study that, if not accounted for, could negatively affect (i.e. confound) the data subsequently collected.

Such factors potentially prevent researchers from finding a direct causal effect between the manipulated independent variables (IVs) and measured dependent variables (DVs) set out in an investigation.

The following two methods can be used for controlling the impact of extraneous variables:

1.) Randomization: Theoretically, randomization is the only method of controlling all possible extraneous variables. The random assignment of subjects to the various treatment and control groups means that the groups can be considered statistically equal in all ways at the beginning of the experiment. It does not mean that they actually are equal to all variables.

However, the probability of their being equal is greater than the probability of their not being equal, if the random assignment was carried out properly. The exception lies with small groups where random assignment could result in an unequal distribution of crucial variables. If this possibility exists, the other method would be more appropriate. In most instances, however, randomization is the best method of controlling extraneous variables.

A random sampling technique results in a normal distribution of extraneous variables in the sample; this approximates the distribution of those variables in the population. The purpose of randomization is to ensure a representative sample.

Randomization comes into play when we randomly assign subjects to experimental and control groups, thus ensuring that the groups are as equivalent as possible prior to the manipulation of the independent variable. Random assignment assures that the researcher is unbiased. Instead, the assignment is predetermined for each subject.

2.) Matching: When randomization is not possible, or when the experimental groups are too small and contain some crucial variables, subjects can be matched for those variables. The experimenter chooses subjects who match each other for the specified variables. One of these matched subjects is assigned to the control group and the other to the experimental group, thus ensuring the equality of the groups at the outset.

The process of matching is time-consuming and introduces considerable subjectivity into sample selection. Therefore, it should be avoided whenever possible. If we use matching, limit the number of groups to be matched and keep the number of variables for which the subjects are matched low. Matching with more than five variables becomes extremely cumbersome, and it is almost impossible to find enough matched partners for the sample. Matching may be used in all research designs when we are looking at certain outcomes & want to have as much control as possible.