Assessing Normality Is the data normally distributed 2

Assessing Normality Is the data normally distributed?

2. 3 Assessing Normality �In this section, we will see how to determine if data is normally distributed or not. �We will look at 3 things to help determine if data is normal.

Assessing Normality �If data is normally distributed: 1. The mean and median should be very close or equal. 2. A histogram (or dot-plot) should show a bell-shaped, symmetric pattern with 1 mode.

Assessing Normality � 3. A normal plot will produce approximately a linear relationship IF the data is normal. �We will create these plots on the calculator

Example #1 �A professor measured the time it took him to drive to work on 42 days. See problem #1. 49 on page 53. � Let’s test this data for normality:

Example #1 Conclusion: � The mean and median are approximately equal. � The histogram is approximately bell shaped. � The normal probability plot shows a linear trend. THIS DATA DOES APPROXIMATE A NORMAL DISTRIBUTION �

Example #2 �A die (6 -sided) is rolled 100 times and the results are entered into a list. �Do we expect the list to follow a normal? ?

Example #2 Conclusion �Since the histogram does not show a symmetric, bell-shaped distribution, the data is NOT NORMAL! �Also The normal plot is not linear!