A way to attract respondents. allowing to ensure the representativeness of the population studied. and thus a high external validity of the experiment between groups. Two of the main group-building strategies are used to test people. Any two effective group comparison schemes – randomized group testing and randomized group testing with stratified preselection (or stratified randomized testing of individual strata).

The latter scheme (taking into account the adequacy of the principle of separation of the layers of the studied activity) makes it possible to achieve higher external validity with the same number of topics. In the given schemes. O. With the subjects distributed in groups. so that it provides not only external validity. but also provides automatic and high internal validity.