It is rather trivial to make tests reliable -- ie, to give the same result each application. IQ tests are highly reliable. But about measuring what? They measure g, general intelligence, taken to mean the average performance of an individual over a range of reasoning skills. The validity of IQ tests, then, only relates to their ability to measure what is taken as g. Their results do historically correlate highly with school performance, but they do so in a declining fashion, that is, starting high in elementary school and reaching a fairly weak correlation by graduation school. This can be interpreted as the tests being highly similar to school testing, thus constituting an alternate measure of the same skills, or to success in graduate school being more related to social or other skills, rather than intelligence.
I tend to think it is the former, and that if IQ scores are declining, the teaching of, modeling of, and practice of using basic reasoning skills might be experiencing a decline, especially vis-a-vis the change to screen-based media. In short, physical interaction with the environment is the age-old method for animal learning, and the simple acts of physically taking notes and making outline summaries of schoolbook chapters (giving structure to information and physically putting that framework down on paper) might be what is missing in a relative sense.
But it is irksome, to say the least, to hear some Trumpling utter articles of religious faith about how the world works, all while simultaneously carrying a mobile phone with GPS. I do not know what kind of dumb that is, but stubborn dumb is a far worse epidemic than declining test scores.
