Conductive polymer was also developed at Penn by Alan J. Heeger, Alan MacDiarmid and Hideki Shirakawa, an invention that earned them the Nobel Prize in Chemistry. On faculty since 1965, Ralph L. Brinster developed the scientific basis for in vitro fertilization and the transgenic mouse at Penn and was awarded the National Medal of Science in 2010. The theory of superconductivity was also partly developed at Penn, by then-faculty member John Robert Schrieffer (along with John Bardeen and Leon Cooper). The university has also contributed major advancements in the fields of economics and management. Among the many discoveries are conjoint analysis, widely used as a predictive tool especially in market research, Simon Kuznets's method of measuring Gross National Product, the Penn effect (the observation that consumer price levels in richer countries are systematically higher than in poorer ones) and the "Wharton Model" developed by Nobel-laureate Lawrence Klein to measure and forecast economic activity. The idea behind Health Maintenance Organizations also belonged to Penn professor Robert Eilers, who put it into practice during then-President Nixon's health reform in the 1970s.