Question

Athletes performing in bright sunlight often smear black eye grease under their eyes to reduce glare. Does eye grease work? In one study, 16 student subjects took a test of sensitivity to contrast after three hours facing into bright sun, both with and without eye grease. (Greater sensitivity to contrast improves vision and glare reduces sensitivity to contrast.) This is a matched pairs design. Here are the differences in sensitivity, with eye grease minus without eye grease.

0.06	0.65	−0.12	−0.04	−0.19	0.14	−0.16	0.03
0.05	0.02	0.44	0.25	−0.12	0.28	0.04	0.28

How much more sensitive to contrast are athletes with eye grease than without eye grease? Give a 99% confidence interval to answer this question. (Round your answer to three decimal places.)

_________ to ___________

Answer 1

0.06	-0.041	0.001681
0.05	-0.051	0.002601
0.65	0.549	0.301401
0.02	-0.081	0.006561
-0.12	-0.221	0.048841
0.44	0.339	0.114921
-0.04	-0.141	0.019881
0.25	0.149	0.022201
-0.19	-0.291	0.084681
-0.12	-0.221	0.048841
0.14	0.039	0.001521
0.28	0.179	0.032041
-0.16	-0.261	0.068121
0.04	-0.061	0.003721
0.03	-0.071	0.005041
0.28	0.179	0.032041

Refer t-table or use excel function "=T.INV.2T(0.01,15)" to find the critical value of t.