BI 152 Week 13 Spr. 11 Name _______________________________
There are many statistical tests – see p. 50 in Ambrose for the decision tree.
Notice the terms Parametric and Nonparametric
Parametric tests assume several things
The data are continuous (you can do averages)
The data are normally distributed
Nonparametric tests are used when
The distribution shape is not normal or is unknown, or,
The data are discontinuous
The X 2 test is an example of a nonparametric test
It is a parametric evaluation of the means of independent samples. In figure on p. 43. You can see two normal distributions whose means are different. But are they different enough?
The t-Test answers the question:
Are the sample means different enough to reject the null hypothesis of no difference?
If you want to see how to calculate the tTest by hand, go to page 86.
Excel and many online calculators will do this for you. We will use graphpad
Example: Sample data for Flustop
Number of days with symptoms
Given Flu Stop Not given Flustop
4
4
6
4
5
4
6
7
5
5
4
7
4
5
5
7
5
4
6
6
4
7
7
6
5
4
4
6
6
4
1

BI 152 Week 13 Spr. 11 Name _______________________________
Let’s do this with excel and with http://www.graphpad.com/quickcalcs/ttest1.cfm
What was the t statistic?
What is your conclusion?
Have you made a Type I or Type II error? How do you know?
2