Subhotosh, like I mentioned in a previous message my textbook isn't very good about giving information or going into much detail about the terms. All it mentions is the definitions for internal validity and external validity. Internal Validity is defined as, "The extent to which the results of an experiment can be attributed to the manipulation of the independent variable rather than to some confounding variable." External Validity is defined as, "The extent to which the results of an experiment can be generalized."