Piaget found that high school students in elite schools in Geneva, Switzerland, were more likely to demonstrate formal operational thought (his highest level of intellectual development) than were adolescents and adults with less rigorous scientific training. This has been linked to the specific tests he used, which involved the solving of basic physics problems. As mentioned above, our intelligence develops through solving problems that are directly relevant to us. Tests that do not take ecological validity into account, therefore, are likely to be culturally biased. Ecological validity refers to the extent to which a given test is appropriate to the context in which it is being used.