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Typing Speed
Determine whether the data for typing speeds are normally distributed. Tree Weights
Test the normality of tree weights for regression analysis. |
Typing Speed: Problem |
Three brands of typewriters were tested for typing speed by having expert typists type identical passages of text.
Perform the Shapiro-Wilk test to test that the typing speeds have a normal distribution. |
Lee Creighton (modified by Paris Faison)
SAS Institute
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Typing Speed: Sample Data | |
The Typing_speed data set is from a test in which three brands of typewriters were tested for typing speed by 17 expert typists. These are the variables in the data set: Name | Type | Description | | brand | char | brand of typewriter | | speed | num | typing speed (words per minute) | |
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Source of Data
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Sall, J., Creighton, L., & Lehman, A. (2006). JMP Start Statistics, Third Edition. Cary, NC: SAS Institute Inc. |
Typing Speed: Solution |
The output for the Shapiro-Wilk test (generated by using SAS Enterprise Guide) yields a p-value of 0.9214. This indicates that we cannot conclude that the typing speed data are non-Normal. |
Tree Weights: Problem |
A forestry commission once sought a way to accurately estimate the weights of trees without having to go through the damaging process of cutting the trees down to weigh them. The weights and trunk girths of 104 tree specimens were measured, in hopes that girth would be useful in predicting weight.
Begin checking the conditions for the simple linear regression analysis by performing a test for normality for the response, tree weight. |
SAS Institute Inc.
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Tree Weights: Sample Data | |
The Tree data set contains data about the weights and trunk girths of 104 tree specimens (eight specimens from each of thirteen rootstocks). These are the variables in the data set: Name | Type | Description | | RootStock | char | rootstock (I – XIII) | | TrunkGirth | num | trunk girth of specimen | | Weight | num | weight of specimen | |
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Source of Data
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This data is sample data from SAS Institute Inc. |
Tree Weights: Solution |
You can base your conclusion on any of the following four test results: Shapiro-Wilk, Kolmogorov-Smirnov, Cramer-von Mises, and Anderson-Darling. For instance, using the Shapiro-Wilk test, the outcome is not significant (at a level as high as α = 0.10), since the p -value = 0.1235. So, we do not have strong enough evidence to reject to null hypothesis of normality. Hence, we cannot claim that the condition for the normality of tree weights is violated (i.e., fail to reject H0). |
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