Exercises on t-tests and confidence intervals

 

Exercise 1

In a study one group of test animals was given a certain soft steroid, while another group was given no such steroids. After a period the increase in weight (in grams) was measured, and gave the results reported in the table:

 

Treatment	Sample size	Sample mean	Sample standard deviation
Steriod	8	32.8	2.6
Control	10	40.5	2.5

 

Find a 90 % confidence interval for the difference in weight increase for the two groups.

 

 

 

Exercise 2

In a study a group of men was given calcium supplement for 12 weeks, while a control group got no such supplement. The reduction in systolic blood pressure was measured and gave the result reported in the table:

 

Treatment	Sample size	Sample mean	Sample standard deviation
Calcium group	10	5.00	8.74
Control group	11	-0.27	5.90

 

Perform a t-test to decide whether the intake of calcium reduces the systolic blood pressure.

 

 

Exercise 3

In a study the strength of seven fabrics was tested in both an unabraded condition and in an abraded condition. The following breaking loads (in kg/25 mm width) were recorded:

 

	1	2	3	4	5	6	7
Unabraded	36.4	51.5	38.7	43.2	48.8	25.6	49.8
Abraded	28.5	46.0	34.5	36.5	52.5	26.5	46.5
Difference	7.9	5.5	4.2