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 makes the experiment easier to conduct since we can apply the insecticide in any pattern rather than in a systematic fashion.

(b) 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.

(c) Random assignment makes the analysis easier since the data can be collected and entered into the computer in any order.

(d) Random assignment is required by statistical consultants before they will help you analyze the experiment.

(e) Random assignment implies that it is not necessary to be careful during the experiment, during data collection, and during data analysis.

Short answer

The correct option is (b).

Step-by-step solution

Given information

Consider doing an experiment to determine the effectiveness of various insecticides in controlling pests and their impact on tomato plant productivity.

Concept

The random assignment method assigns subjects to treatments based on chance. Before the treatments are applied, random assignment establishes treatment groups that are comparable (except for chance variance). In experiments, randomization and comparison combined prevent bias or systematic favoritism.

Explanation

Consider doing an experiment to determine the effectiveness of various insecticides in controlling pests and their impact on tomato plant productivity. What is the most compelling justification for assigning treatment levels (spraying or not spraying) to experimental units (farms) at random? (a)Using a random assignment, researchers can draw broad generalizations regarding insecticide effectiveness across all farms. (b) Random assignment will tend to average out all other uncontrolled parameters like soil fertility, ensuring that treatment effects are not confounded. (c) The impacts of other variables, such as soil fertility, are eliminated by random assignment. (d) Random assignment eliminates response variability due to chance. (e) The placebo effect is mitigated by random assignment.

You can assign those individuals to either of the two assignments at random. By allocating treatments at random, we hope to make the different groups look as comparable as possible, reducing the chance of a confounding variable. As a result, option (b) is correct.