For an experiment on the impacts of the pesticide carbaryl and the presence of a

Question

For an experiment on the impacts of the pesticide carbaryl and the presence of a predator, the red-spotted, newt on tadpole survival the tadpoles were placed into four different groups of tubs:

water only and no predator

water only with a predator visible

pesticide dosed water with no predator

pesticide dosed water with a predator visible

It was observed that tadpoles in the water only tubs had a 90+% survival rate regardless of the presence of a predator. The tadpoles in the pesticide dosed water however were strongly divided with 90+% of tadpoles surviving when there was no predator present and less than 20% surviving in the presence of a predator.

Does this experiment demonstrate interaction between the two treatments?

2. Is it possible to reduce the effects of confounding variables on a difference between treatments in a controlled observational study by employing matching? yes or No

Explanation / Answer

1.

Yes. This experiment shows interaction between the two treatments.

In the earlier two cases when there was no pesticide, the survival rate was 90+%. So here it is clear that there is no effect of predator.

In the last two cases when there was pesticide, the survival rate was 90+% in without predator case and only 20% in presence of predator. This shows that the combination of predator in presence of pesticide led to the the less survival rate.

So it is clear that

a) Only predator does not affect the tadpole survival rate.

b) Only pesticide also does not affect the tadpole survival rate.

c) But when pesticide with predator are present then the tadpole survival rate goes down.

2.

Yes. It is possible to reduce the effect of confounding variables on a difference between treatments in a controlled observational study by employing matching. Ways to do it are as follows

Random sampling :- Keep sampling as random as possible.

Control variables :- Introduce control variables like age, etc.

Keep a record of what happened to the samples between the study.

Counterbalancing :- Test the sample by making small groups.

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