Question

1. researchers have developed a liquid repellant intended to keep porcupines from gnawing on wooden bridges in a local park. the researchers will conduct a well - designed experiment to test the effectiveness of the repellant by placing wooden stakes in the ground and randomly assigning them to receive either the repellant or a placebo treatment. which of the following is true about this experiment? a) the experiment cannot provide sufficient evidence that the repellant causes the porcupines to avoid stakes; only an association can be demonstrated. b) any non - zero difference in gnawing behavior will provide sufficient evidence that the repellant causes the porcupines to avoid gnawing on the stakes. c) the experiment cannot be used to show the repellant causes the porcupines to avoid stakes, since the repellant is not being compared to other repellants on the market. d) the difference in the amounts of gnawing behavior on stakes given the two treatments must be statistically significant to provide sufficient evidence that the repellant is effectiv e) all stakes with the repellant would need to have less gnawing than all stakes with the placebo to provide sufficient evidence that the repellant is effective.

Explanation:

• In an experiment, to conclude that a treatment (here, the repellant) is effective, the difference in the response (gnawing behavior) between the treatment group (repellant) and the control group (placebo) should be statistically significant. Statistical significance helps in determining that the observed difference is not due to random chance.
• Option A is incorrect because a well - designed experiment (with random assignment) can provide evidence of causation, not just association.
• Option B is wrong as a non - zero difference could be due to random variation. We need to check for statistical significance.
• Option C is incorrect. Comparing with a placebo (a non - treatment) is a valid way to test if the repellant works, and we don't need to compare with other repellants on the market for this basic effectiveness test.
• Option E is too strict. We don't need all stakes with the repellant to have less gnawing than all placebo stakes. A significant difference in the overall (average or proportion) gnawing behavior is sufficient.

Answer:

D. The difference in the amounts of gnawing behavior on stakes given the two treatments must be statistically significant to provide sufficient evidence that the repellant is effective.