As part of my research, I have to analyse 10 years time series financial data of four public limited companies through Multiple Linear Regression. First I analysed each company separately using Regression. The adjusted R square value is above 95% and VIF is well within limits but Durbin-watson measure shows either 2.4, 2.6 or 1.1 etc which signifies either positive or negative auto correlation. Then I tried the model with the combined data of all the four companies. This results in very less adjusted R squared value (35%) and again a positive auto correlation of 0.94 Durbin-Watson . As I am trying DuPont Analysis where the dependent variable is Return on Equity and independent variables are Net Profit Margin, Total Asset Turnover and Equity Multiplier, which are fixed, I cannot change the independent variables to reduce the effect of auto correlation. Please suggest me what to do.