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Normal probability plot
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<p> The normal probability plot is a <a href="/facts/Graphical_technique/SAo9EjFx">graphical technique</a> to identify substantive departures from <a href="/facts/Normal_distribution/UapjjPyQ">normality</a>. This includes identifying <a href="/facts/Outlier/VBhIzGbx">outliers</a>, <a href="/facts/Skewness/rdS8luFa">skewness</a>, <a href="/facts/Kurtosis/yqGgry89">kurtosis</a>, a need for transformations, and <a href="/facts/Mixture_distribution/BMdA5kTI">mixtures</a>. Normal probability plots are made of raw data, <a href="/facts/Errors_and_residuals_in_statistics/Ef0LgAS4">residuals from model fits</a>, and estimated parameters. </p> <p>In a normal probability plot (also called a "normal plot"), the sorted data are plotted vs. values selected to make the resulting image look close to a straight line if the data are approximately normally distributed. Deviations from a straight line suggest departures from normality. The plotting can be manually performed by using a special <a href="/facts/Graph_paper/NKJBaxCS">graph paper</a>, called <i>normal probability paper</i>. With modern computers normal plots are commonly made with software. </p><p>The normal probability plot is a special case of the <a href="/facts/Q%E2%80%93Q_plot/h2jKBjYm">Q–Q</a> probability plot for a normal distribution. The theoretical <a href="/facts/Quantile/oWr1MC3s">quantiles</a> are generally chosen to approximate either the mean or the median of the corresponding <a href="/facts/Order_statistic/QS3RnGcC">order statistics</a>. </p>