a Stone use 1929-1938 data in usa and receive 17 variables which describe income-pay. He used principle component analysis and got three new variables fl. f2, F3. fl total income F2, total income increase ratio F3, economy increase or decrease. These new variable can use three variables(l △I、t) which can be measured directl 2021/1/212021/1/21 4 cxt  Stone use 1929一1938 data in USA, and receive 17 variables which describe income-pay. He used principle component analysis and got three new variables F1、F2、F3. F1, total income;F2,total income increase ratio;F3,economy increase or decrease. These new variable can use three variables (I、 I、t ）which can be measured directly