The term validity means how correct the results in an experiment are. Internal validity measures how correct the results are from within the experiment It ensures that the variables that are meant to be manipulated are the actual one manipulated (Myers, & Hansen, 2012). External validity measures how well the results of an experiment can be generalized to the population outside of the experiment. There are a few ways to increase external validity; aggregation, multivariate designs, non-reactive measures, field experiments, and natural observation. When using aggregation, a researcher gathers the data and averages it in different ways (Myers, & Hansen, 2012). The four types of aggregation are over subject, over stimuli/situations, over trails/occasions, and over measure. Multivariate design lets researchers analyze multiple dependent variables at one time. It lets look at a combination of variables that will generalize the population outside the experiment better. There are a few ways that researchers can increase internal validity; they need to properly define their variables, set up their measuring techniques properly, and make sure they have the proper number of participants to test their hypothesis.