International Journal of Economics and Finance; Vol. 10, No. 11; 2018 ISSN 1916-971X E-ISSN 1916-9728 Published by Canadian Center of Science and Education Phillips Curve Is a Particular Case that Economists Misinterpret the Correlation between Two Dependent Variables for Causal Relation Chao Chiung Ting1 1 Graduated from Michigan State University, USA Correspondence: Chao Chiung Ting, Graduated from Michigan State University, 63 33 98th Place 1E, Rego Park, NY 11374, USA. E-mail:
[email protected] Received: September 5, 2018 Accepted: October 18, 2018 Online Published: October 25, 2018 doi:10.5539/ijef.v10n11p70 URL: https://doi.org/10.5539/ijef.v10n11p70 Abstract Since labor supply and labor demand determines both employment and wage in labor market endogenously, both wage and employment, which we observe, are dependent variable in the sense of ex-post. Since unemployment is equal to labor supply minus labor demand, unemployment is dependent variable in the sense of ex-post, too. There is no causal relation between two dependent variables because independent variable explains dependent variable. Thus, the relationship between ex-post unemployment and ex-post wage in Phillips (1958) is not causal relation but correlation as meaningless as the strong correlation between ice cream sale and drowning rate. Similarly, both price and quantity we observe are determined by supply and demand endogenously in the sense of ex-post. Thus, inflation rate is dependent variable because inflation rate is the change in price level (i.e., change in the average price of all goods in the sense of ex-post). Hence, we are not permitted to explain unemployment rate by inflation rate and vice versa.