Despite the fact that Kalecki authored many theoretical economic constructs, his interest in economics was more practical than academic and resulted from his work in engineering, journalism, credit investigation, use of statistics and observation of business operations. Full-time university teaching, for which he did not have formal qualifications (a degree), he did only during the last thirteen years of his career. He was contemptuous of abstract research and declined Keynes's invitation to undertake a critique of Jan Tinbergen's econometric business cycle work, for which he would also lack an in-depth knowledge of statistical theory.