Recall that, after an angry exchange of emails, the winning procedure for testing Fish2Whale fishfood was:
- Feed normal fish food to one group of fish (the control group) and
- Feed Fish2Whale to another group of fish (the treatment group) and
- See which group grows longer in length.
Here is the data your lab got:
Control group mean length 22 cm, SD 3 cm
Treatment group mean length 25 cm, SD 3 cm
What percentage of the control group fish are between 22 and 25 cm?
What percentage of the treatment group fish are between 22 and 28 cm?
(The numbers worked out quite easily here since I chose exactly the mean and the mean plus 1 SD as the range of interest. However, there are tables which allow you to make the same calculation for any range you’re interested in. We won’t cover them here.)