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pythonrlinear-regressionnormal-distribution

Different results for residual normal distribution between Jarque-Bera test and Q-Q Plot


I am trying to test for normality of residuals using 2 different ways.

  1. Using Jarque-Bera test
  2. Q-Q Plot

I can see different results, for the JB test the probability value is 19.9553 with a probability of 0.00005. Thus, we can't reject the null hypotheses, and this concludes that there is a non-normal distribution of results.

on the other hand, when I plotted the same dataset using Q-Q graph, I could see a partially linear relation, which might point to a normal distribution. Given the size of observations is 62 and the regression model that was used is the OLS model.

enter image description here

Do you think I did something wrong in my assumption?


Solution

  • The QQ graph does not show that the data are normally distributed. If you would calculate a single indicator from a QQ plot, then you would measure the (positive vertical ) distances of the points to the red reference line and sum them up. In your case, almost all points deviate from the reference line, voting for a non-normal distribution.

    A typical QQ plot of normally distributed data has got a large majority of points on the red reference line and some points at the ends (left and right) may deviate.