Threats to Internal Validity Differences Between Online and Traditional Focus Groups

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Internal validity - means that the conclusion which comes from an experiment is valid for the respondents who participated in the experiment. For any experimental design, we always require interval validity, without which experimental results are not interpretable.

Threats to Internal Validity

Selection - Subjects bring with them into the investigation unique characteristics, some learned and some inherent. Examples include sex, height, weight, color, attitude, personality, motor ability, and mental ability. If assigning subjects to comparison groups results in unequal distribution of these subject-related variables, then there is a possible threat to internal validity.

History - the specific events occurring between the first and second measurement in addition to the experimental variable. Suppose that the dependent variable is measured twice for a group of subjects, once at Time A and later at Time B, and that the independent variable is introduced in the interim. Suppose also that Event A occurs between Time A and Time B. If scores on the dependent measure differ at these two times, the discrepancy may be due to the independent variable or to Event A.

Maturation - processes within the respondents operating as a function of the passage of time per se (not specific to the particular events), including growing older, growing hungrier, growing more tired/bored, and the like. Some of these changes are permanent (e.g., biological growth), while others are temporary (e.g., fatigue). Suppose that the dependent variable is measured twice for a group of subjects, once at Time A and later at Time B, and that the independent variable is introduced in the interim. If scores on the dependent measure differ at these two times, the discrepancy may be due to the independent variable or to naturally occurring developmental processes.

Testing - the effects of taking a test upon the scores of a second testing (like soc. desirability). Suppose that the dependent variable is recorded twice for a group of subjects, once at Time A and later at Time B, and that the independent variable is introduced in the interim. If scores on the dependent measure differ at these two times, the discrepancy may be due to the independent variable or to the procedure involved in measuring the dependent variable at Time A.

Instrumentation in which changes in the calibration of a measuring instrument or changes in the observers or scorers used may produce changes in the obtained measurements. Examples include changes in the calibration of a mechanical measuring device as well as the proficiency of a human observer or interviewer. Suppose that the dependent variable is measured twice for a group of subjects, once at Time A and later at Time B, and that the independent variable is introduced in the interim. Suppose also that the ability of a recording device to detect instances of the target behavior improves (declines) as the experiment progresses. If scores on the dependent measure differ at these two times, the discrepancy may be due to the independent variable or to more/less sensitive recordings of the target behavior at Time B relative to at Time A.

Regression - -operating where groups have been selected on the basis of their extreme scores (e.g., bootcamps for troubled teenagers). Take any dependent measure that is repeatedly sampled, move along it as in a time dimension, and pick a point that is the "highest/lowest so far. On the average, the next point will be lower/higher, nearer the general trend." Suppose that the dependent variable is measured twice for a group of subjects, once at Time A and later at Time B, and that the independent variable is introduced in the interim. Suppose also that value observed for subjects at Time A is considerably higher/lower than would typically be the case. If scores on the dependent measure differ at these two times, it may be due to the independent...
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