Question

Consider an experiment to investigate the effectiveness of different insecticides in

controlling pests and their impact on the productivity of tomato plants. What is the best

reason for randomly assigning treatment levels (spraying or not spraying) to the

experimental units (farms)?

a. Random assignment eliminates the effects of other variables, like soil fertility.

b. Random assignment eliminates chance variation in the responses.

c. Random assignment allows researchers to generalize conclusions about the

effectiveness of the insecticides to all farms.

d. Random assignment will tend to average out all other uncontrolled factors such as

soil fertility so that they are not confounded with the treatment effects.

e. Random assignment helps avoid bias due to the placebo effect.

Short answer

The correct option is:

d. Random assignment will tend to average out all other uncontrolled factors such as soil fertility so that they are not confounded with the treatment effects.

Step-by-step solution

Given information

We have been given four options from which we have to select the correct one.

a. Random assignment eliminates the effects of other variables, like soil fertility.

b. Random assignment eliminates chance variation in the responses.

c. Random assignment allows researchers to generalize conclusions about the

effectiveness of the insecticides to all farms.

d. Random assignment will tend to average out all other uncontrolled factors such as

soil fertility so that they are not confounded with the treatment effects.

e. Random assignment helps avoid bias due to the placebo effect.

Explanation

The most compelling rationale for randomization is to reduce the impact of any uncontrollable variables.Random assignment will tend to average out all other controllable variables, such as soil fertility, so that treatment effects are not confounded.