You are actually measuring what you are intended to measure. The presence of an artifact indicates a lack of internal validity; that is, the study has failed to investigate its hypothesis. Children who view television for extended periods have lower grade point averages in school than children who watch only a limited amount of television. Artifact Children who view fewer hours of television also receive parental help with their school work; parental help (the artifact), not hours of television viewed, may be the reason for the difference in grade.