A research study or experiment has internal validity if the outcome is a result of the variables that are measured, controlled or manipulated. Internal validity is only relevant in studies that try to establish a causal relationship. For studies that assess the effects of social programs or interventions, internal validity is the primary consideration. The main question in internal validity is whether the observed changes can be directly attributed to the program or intervention that was implemented and not some other factor. There are eight threats to internal validity. These are criticisms that critics will raise when you try to conclude that your program caused the out come. The eight threats are history, maturation, testing, selection bias, statistical regression, instrumentation, selection maturation and mortality. The first threat I will discuss will be history.
History refers to the idea that something or some event in the subject's life that happened before the study caused them to answer the way they did. For example, if one is conducting a study of math achievement in first graders a TV show like Sesame Street may have caused them to answer the way they did and not the program that was implemented in the study.
Maturation is another threat to internal validity. Maturation is just the normal maturation and growth that occurs as part of growing up. In other words, the math program that may have been implemented had no effect on the students, it is just normal growth in understanding that helped them to learn the math. Maturation is different from history in that it is not referring to a specific event that caused someone to answer in a certain way, it is simply growing up over time.
Another threat to internal validity is testing. This threat only occurs in the pre-post design which is where and pre-test and a post-test are given. The testing threat may occur if taking the pretest made them more aware of the kind of problems they were going to be dealing with in the study.