Although Piaget downplayed the role of environment in cognitive development, much research has shown that adults vary considerably in their demonstration of the cognitive skills associated with formal operational thought. Piaget based his studies on adolescents in prestigious schools that specifically taught the skills of the scientific method. Thus, it is not surprising that adolescents and adults without the same educational advantages would not perform as well in the tests of basic physics that Piaget used to measure formal operational thought. However, there is evidence that adolescents and adults can show hypothetico-deductive reasoning in areas that are relevant to their day-to-day lives. For example, Kalahari bushmen show hypothetico-deductive reasoning when analyzing animal tracks. Thus the concept of formal operations appears to be valid, but the tests that measure it need to have ecological validity, that is they need to be appropriate to the situation at hand.