there was a question regrarding internal vailidty in social science research, kindly share material regarding it or refer some book to consult it.
thank you

The easy way to describe internal validity is the confidence that we can place in the cause and effect relationship in a study. The key question that you should ask in any experiment is:

“Could there be an alternative cause, or causes, that explain my observations and results?”

Factors which jeopardize internal validity
History: the specific events which occur between the first and second measurement.

Maturation: the processes within subjects which act as a function of the passage of time. i.e. if the project lasts a few years, most participants may improve their performance regardless of treatment.

Testing: the effects of taking a test on the outcomes of taking a second test.

Instrumentation: the changes in the instrument, observers, or scorers which may produce changes in outcomes.

Statistical regression: It is also known as regression to the mean. This threat is caused by the selection of subjects on the basis of extreme scores or characteristics. Give me forty worst students and I guarantee that they will show immediate improvement right after my treatment.

Selection of subjects: the biases which may result in selection of comparison groups. Randomization (Random assignment) of group membership is a counter-attack against this threat. However, when the sample size is small, randomization may lead to Simpson Paradox, which has been discussed in an earlier lesson.

Experimental mortality: the loss of subjects. For example, in a Web-based instruction project entitled Eruditio, it started with 161 subjects and only 95 of them completed the entire module. Those who stayed in the project all the way to end may be more motivated to learn and thus achieved higher performance.

Selection-maturation interaction: the selection of comparison groups and maturation interacting which may lead to confounding outcomes, and erroneous interpretation that the treatment caused the effect.

John Henry effect: John Henry was a worker who outperformed a machine under an experimental setting because he was aware that his performance was compared with that of a machine.

INTERNAL VALIDITY – THE FINAL WORD
Just to leave you with an example of how difficult measuring internal validity can be:
In the experiment where researchers compared a computer program for teaching Greek against traditional methods, there are a number of threats to internal validity.


•The group with computers feels special, so they try harder, the Hawthorne Effect.


•The group without computers becomes jealous, and tries harder to prove that they should have been given the chance to use the shiny new technology.


•Alternatively, the group without computers is demoralized and their performance suffers.


•Parents of the children in the computerless group feel that their children are missing out, and complain that all children should be given the opportunity.


•The children talk outside school and compare notes, muddying the water.


•The teachers feel sorry for the children without the program and attempt to compensate, helping the children more than normal.

We are not trying to depress you with these complications, only illustrate how complex internal validity can be.

In fact, perfect internal validity is an unattainable ideal, but any research design must strive towards that perfection.

For those of you wondering whether you picked the right course, don’t worry. Designing experiments with good internal validity is a matter of experience, and becomes much easier over time.

For the scientists who think that social sciences are soft – think again!