3. a researcher wanted to find out whether higher levels of a certain drug given to experimental rats would decrease the time it took them to complete a given maze to find food.
a. why would the researcher have to carry out an experiment rather than an observational study?
b. describe an experiment that the researcher might carry out based on 30 comparable rats and three dosage levels: 0 mg, 1 mg, and 2 mg.

The answer to each question is given below.

Step-by-step explanation:

As the problem states, a researcher is ttrying to find whether higher levels of a drug given to experimental rats would decrease the time it take them complete a maze to find food.

a. As you can see the researcher is aplying different treatments (doses or levels of the drug) to the rats and thats why this is an experimental study not an observational one (in which there are no treatments imposed by the researcher).

b. If the population of rats that are under study consist of 30 individuals and there are three treatments (three levels of the drug: 0 mg, 1 mg and 2 mg), the researcher should assign 10 rats to each treatment. Here the dose of 0 mg acts as a control.

So, each rat will receive its respective dose of drug and then has to do the maze. The researcher will register the time the rat needs to find food. To avoid incidence of the researcher in the assay there will be something that acts as barrier between the rat and the researcher, this way the rat will not see the researcher and will be only focused on finding the food.  

With obtained data, the researcher will evaluate the incidence of the drug on the time the rat completes the maze.    

step-by-step explanation:

step-by-step explanation: