Describe your hypothesis test and get a clean, labeled rejection region diagram in seconds. The shaded critical region, alpha level, and critical values are all drawn and labeled so you can use the diagram in slides, reports, or study notes right away.
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A standard normal curve with both tails shaded beyond z = -1.96 and z = 1.96, labeled for a two-tailed test at alpha = 0.05.
A one-tailed (upper) rejection region on a normal curve at alpha = 0.05, with the right tail shaded beyond z = 1.645.
A one-tailed (lower) rejection region on a normal curve at alpha = 0.05, with the left tail shaded beyond z = -1.645.
A comprehensive two-tailed diagram with alpha areas shaded, critical values annotated, and the acceptance region clearly labeled.
A two-tailed rejection region on a t-distribution with 10 degrees of freedom at alpha = 0.05, with heavier tails than the normal curve.
A two-tailed normal curve with the rejection region shaded and the observed test statistic marked to illustrate the reject or fail-to-reject decision.
Start with one of these examples, then adapt the subject, labels, data, or layout for your own use.
A standard normal curve with both tails shaded beyond z = -1.96 and z = 1.96, labeled for a two-tailed test at alpha = 0.05.
Draw a two-tailed rejection region diagram on a standard normal bell curve at alpha = 0.05. Shade both tails beyond z = -1.96 and z = 1.96. Label the critical values, alpha/2 = 0.025 in each tail, and the acceptance region in the center. Classic textbook style. White background.
A one-tailed (upper) rejection region on a normal curve at alpha = 0.05, with the right tail shaded beyond z = 1.645.
Draw a right-tailed rejection region diagram on a standard normal bell curve at alpha = 0.05. Shade the upper tail beyond z = 1.645. Label the critical value, alpha = 0.05 in the shaded area, and the non-rejection region to the left. Classic style. White background.
A one-tailed (lower) rejection region on a normal curve at alpha = 0.05, with the left tail shaded beyond z = -1.645.
Draw a left-tailed rejection region diagram on a standard normal bell curve at alpha = 0.05. Shade the lower tail to the left of z = -1.645. Label the critical value, alpha = 0.05 in the shaded area, and the non-rejection region to the right. Classic style. White background.
A comprehensive two-tailed diagram with alpha areas shaded, critical values annotated, and the acceptance region clearly labeled.
Draw a detailed two-tailed rejection region diagram on a normal curve at alpha = 0.01. Shade both tails beyond z = -2.576 and z = 2.576. Annotate the critical values on the x-axis, label "Rejection Region" in each tail with alpha/2 = 0.005, and "Fail to Reject H0" in the center. Colorful style. White background.
A rejection region diagram is a visual used in hypothesis testing to show which values of a test statistic would lead you to reject the null hypothesis. It plots the sampling distribution (usually a normal curve or t-distribution), then shades the area in one or both tails beyond the critical value. That shaded area is the rejection region (also called the critical region). If your calculated test statistic falls inside it, you reject the null hypothesis. Figviz generates these diagrams from a plain description so you get a clean, labeled visual without having to draw and annotate by hand.
A two-tailed test splits alpha equally between both tails (alpha/2 each), which is appropriate when the alternative hypothesis is simply that the parameter differs from the null value in either direction. A right-tailed test places all of alpha in the upper tail and is used when the alternative is that the parameter is greater than the null value. A left-tailed test places all of alpha in the lower tail for alternatives claiming the parameter is smaller. For a standard normal distribution at alpha = 0.05, the two-tailed critical values are z = plus or minus 1.96, the right-tailed critical value is z = 1.645, and the left-tailed critical value is z = -1.645. The shape of the rejection region changes accordingly, and Figviz will draw whichever form you describe.
Always specify the significance level alpha and the critical value(s) in your prompt so the diagram matches your specific test. For t-distributions, include the degrees of freedom because the critical value changes with sample size (for example, t = 2.228 at df = 10 versus t = 2.042 at df = 30). If you want to illustrate the decision rule, ask for the observed test statistic to be marked on the diagram as a vertical line or arrow. Label the acceptance region and rejection region explicitly to make the diagram self-explanatory for readers who are new to hypothesis testing.
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