Welcome to this lesson where we are going to discuss threats to internal and external validity of experimental designs. Experimental procedures establishes causality, i.e. it allows the researcher to conclude that variable X causes variable Y. For a researcher to make this conclusion, s/he must ensure that there are no spurious relationships and all extraneous variables are concerned

Threats are factors that threatens the confidence of a researcher to conclude that X causes Y.

There are two types of threats:

1. Threats to internal validity of the experimental design
2. Threats to external validity of the experimental design

Internal and external validity are concepts that reflect whether or not the results of a study are trustworthy and meaningful. This lesson will discuss these concepts in details.