Regression line comparison

 

For difference of r1 and r2

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for difference of b1 and b2 (the difference between slopes)

standard error of the difference between the two slopes based on the standard error of each slope for large samples is better to be calculated as:

 

for smaller samples find the pooled residual variance=

standard error of the difference between slopes=

and use t statistics

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the difference of intercepts a1 and a2

M1 and M2 are the means on the predictor variable for the two groups

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For Comparing Regression Lines From Independent Samples when one wishes to determine whether the linear relationship between one continuously distributed criterion variable and one or more continuously distributed predictor variables differs across levels of a categorical variable see:

http://core.ecu.edu/psyc/wuenschk/MV/multReg/Potthoff.pdf

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References:

Using the correct statistical test for the equality of regression coefficients
R Paternoster, R Brame, P Mazerolle, A Piquero
Criminology 36 (4), 859-866

Wuensch, K. L.  (2013).  Comparing Correlation Coefficients, Slopes, and Intercepts Retrieved, from http://core.ecu.edu/psyc/wuenschk/docs30/CompareCorrCoeff.pdf on the 12th of October, 2013.