# Are the Distributions Normal?

The tests of normality overlay a normal curve on actual data, to assess the fit. A significant test means the fit is poor. For the standard alloy, the test is not significant; they fit the normal curve well. However, for the premium alloy, the test is significant; they fit the normal curve poorly.

**Stem-and-leaf plots** use the original
data values to display the distribution's shape. The plot for premium
bearings visualizes the positive skew statistic seen in the descriptives
table; the values cluster uniformly in a range of 1530 to 1543 degrees,
then disperse gradually at the higher temperatures.

Finally, a **Q-Q** plot is displayed. The straight
line in the plot represents expected values when the data are normally
distributed. The observed premium bearing values deviate markedly
from that line, especially as temperature increases.