In the design, instrumentation effect can be checked and prevented with application of the
same instrument by two different data collectors who have different gender during the study and can
be evaluated by checking the results on test-retest application and trends in pre-test and post-test
applications. Use of two pre-testing and two post-testing is also important for test-retest reliability
calculation and to check regression effect. By this way, we can decide about the situation by only
checking first pre-test results. At the same time, test-retest reliability for each application can also be
investigated by using such a way. Cook and Sinha (2006) explained that multiple pre-testing permits
better control over assignment bias and provides valuable information about cause-effect relationship.