Descriptive Methods for Assessing Normality

Determining Whether the Data Are From an Approximately Normal Distribution

1. Construct either a histrogram or stem-and-leaf display for the data and note the shape of the graph. If the data are approximately normal, the shape of the histogram or stem-and-leaf display will be similar to the normal curve.

2. Compute the intervals (-, +), (-2, +2), and (-3, +3) determine the percentage of measurements falling in each. If the data are approximately normal, the percentage will be approximately equal to 68%, 95%, and 100%, respectely.

3. Find the interquartile range, IQR, and standard deviation,s, for the sample, then calculate the ratio IQR/s. if the data are approximately normal, then IQR/s = 1.3.

4. Construct a normal probability plot for the data. If the data are approximately normal, the point will fall (approximately) on a straight line.

Дата добавления: 2014-01-11