Data
analysis
DP Biology
Standard Deviation and T-test
Problem 1:
1. Find the mean, for the following set of data about daisy leaf width in a grassland.
3.6, 3.8, 4.0, 4.1, 4.4, 4.4, 4.4, 4.5, 4.5, 4.5, 4.5, 4.5, 4.7, 4.8, 4.8, 4.8, 5.0, 5.1, 5.3, 5.4, 5.4, 5.5, 5.7, 6.4, 6.5.
Mean
=
1. Calculate the sd for the data on leaf
1sd = ____________________
68% of the values lie within the range
_____________________________
Standard Deviation
2. Calculate the sd for the following data on daisy leaf width in a wooded area.
5.6, 3.7, 6.9, 7.5, 3.9, 4.4, 7.8, 6.7, 6.7, 6.8, 4.2, 4.5, 8.0, 5.0, 6.3, 4.0, 6.8, 6.0, 4.7, 4.8, 6.6, 7.0, 7.0, 7.2, 7.5, 4.6,
6.9, 7.0
1sd = ____________________
68% of the values lie within the range
_____________________________
3. Compare the mean and the sd for the two populations. How similar are the two populations. Give reasons for your
answers.
Student t test
The t test provides a way of measuring the overlap between two sets of data. If two sets of data have widely separated
means and small variances, they will have little overlap and the p value will be greater than 0.05. If the two sets of data
have means that are close together and large variances they will have a large overlap and a p value less than 0.05.
If p=0.05, the probabilty that the difference is due to chance is only 5%. That means that there is a 95% chance that the
two sets of data are different. A 95% chance is significant in statistics.
4. Carry out a t test on the two sets of data for the daisy leaf size.
a. Formulate hypothesis
Ho _____________________________________________________
Hi _____________________________________________________
c. Is there a significant difference in the daisy leaf width of the two sites? Which hypothesis do you accept
Problem 2:
A study was designed to test the hypothesis that men have a higher diastolic blood pressure than do women. The
data is as follows:
Males: 76
72
76
96
74
80
70
80
68
90
70
90
72
76
80
68
Females:76
70
82
90
68
60
62
68
80
74
60
62
72
Identify the mean. Then determine the standard deviation for each set of data. Finally, conduct a t-test to
determine whether or not there is a difference in diastolic blood pressure. Be sure to include the null hypothesis.