To test effects of weed removal, dissolved oxygen (DO) was evaluated at 10 sites before removal and 10 sites after removal. The data are: DO [mg/l]
Before: 10.6, 9.8, 12.3, 9.7, 8.8, 9.2, 8.8, 10.6, 9.3, 9.5
After: 10.2, 9.4, 11.8, 9.1 8.3, 8.6, 8.1, 10.5, 9.4, 9.1
a) Is there the change in DO levels following weed removal? Determine the 95% confidence interval for the change in DO ?
b) The scientist determining the DO levels later remembered that same ten sites were employed for sampling before and after weed removal. Is there significant difference now?