6.8 Normality Tests 1. Histograms of residuals The histogram of the residuals is used to learn something about the slope of the pdF of a random variable If the histogram of the residuals is close to the picture of the normal distribution, the you can guess H; is normally distributed 2. Normal Probability plot Use normal probabil ity paper the horizontal axis, (X-axis)-values of the variable of interest (OLS residuals e) the vertical axis, (Y-axis)--the expected values of this variable If the variable is in fact from the normal population, the NPP will approximate a straight line6.8 Normality Tests ◼ 1.Histograms of Residuals The histogram of the residuals is used to learn something about the slope of the PDF of a randomvariable. If the histogram of the residuals is close to the picture of the normal distribution, the you can guess μi is normally distributed. ◼ 2. Normal ProbabilityPlot Use normal probability paper: ◼ the horizontal axis,(X-axis)——values of the variable of interest (OLS residuals ei ) ◼ the vertical axis, (Y-axis) ——the expected values of this variable If the variable is in fact from the normal population, the NPP will approximate a straight line