An experimenter wishes to test whether or not two types of fish food (a standard fish food and a new product) work equally well at producing fish of equal weight after a two-month feeding program. The experimenter has two identical fish tanks (1 and 2) to put fish in and is considering how to assign 40 fish, each of which has a numbered tag, to the tanks. The best way to do this would be to

(a) put all the odd-numbered fish in one tank, the even in the other, and give the standard food type to the odd-numbered ones.

(b) obtain pairs of fish whose weights are roughly equal at the start of the experiment and randomly assign one to Tank 1 and the other to Tank 2, with the feed assigned at random to the tanks.

(c) proceed as in part (b), but put the heavier of the pair into Tank 2.

(d) assign the fish completely at random to the two tanks and give the standard feed to Tank 1.

(e) assign the fish to the tanks using any method that the researcher wants. The placebo effect doesn’t apply to fish.