Q-Q Plot

Q-Q plot (quantile-quantile plot) is a probability plot, which is a graphical method for comparing two probability distributions by plotting their quantiles against each other ^[?]. If the two distributions being compared are similar, the points in the Q-Q plot will approximately lie on the line y = x. If the distributions are linearly related, the points in the Q-Q plot will approximately lie on a line, but not necessarily on the line y = x. Q-Q plots can also be used as a graphical means of estimating parameters in a location-scale family of distributions.

Form

• Variablenum

  Select one numerical variable you want to compare with certain distribution.

• Distribution

  Select the distribution to be compared with the variable you select.

• Group byopt

  Select a categorical variable if you want to separate the q-q plot by its group. You can leave this form blank or select "None" of you don't want to group the data.

Example

You can use Caschool dataset (The California Test Score Data Set) to check some numerical variables if it matches certain distribution. You can see that testscr, readscr, and mathscr are normally distributed, while elpct is likely to match the exponential distribution.

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