Chapter 12, Problem 30PT4

To determine

To identify: the best way to allocate 40 fish in two identical tanks 1, 2 to test effectiveness of two types of fish food (standard and new fish food).

Options are

1. Put all odd numbered fish in one tank, the even in the other, and give the standard food type to the odd numbered once.
2. Obtain pairs of fish whose weights are virtually equal at the start of the experiment and randomly assign one to tank 1 and other to tank 2 with the feeds assigned at random to the Tanks.
3. Proceed as in (b) but assign heavier of the pair in Tank2.
4. Assign fish at random to the two tanks and give the standard feed to the Tank1.
5. Not to proceed as in (b) because using the initial weight in part (b) is a non random process. Use the initial length of fish instead.

Answer to Problem 30PT4

Option (b) is best.

(b) Obtain pairs of fish whose weights are virtually equal at the start of the experiment and randomly assign one to tank 1 and other to tank 2 with the feeds assigned at random to the Tanks.

Explanation of Solution

Best way to allocate is (b) as in this way, we are allocating to both tanks randomly and also feed is allocated randomly. This is similar to randomized block design where blocks are tanks and treatments are fish feeds. Also fish with equal weights are selected eliminating bias.

Other designs disadvantages are

(a)Data may have a periodic variation resulting in bias.

(c) Experiment is not randomized here resulting in bias. Blocks should be randomly selected.

(d) Experiment is not randomized here resulting in bias. Treatment should be randomly allocated.

(e) Initial weight is actually reducing the bias but not length.