7. which of the following are true statements? i. in well-designed observational studies, responses are systematically influenced during the collection of the data. ii. in well-designed experiments, the treatments result in responses that are as similar as possible. iii. a well-designed experiment always has a single treatment but may test that treatment at different levels.

The purpose behind random sampling and random assignment is different

Explanation:

In a good study, the response of the subject is not influenced during the collection of the data. in such type of experiment, the treatment is compared to the differences in responses. In an experiment, we can say that there are many levels, factors, and treatment. through random sampling, we can select a population randomly based on our choices. Whatever the findings will be generalized on the population. random assignment in an experiment is used when subjects are randomly assigned to the treatment to put the effects over which we have no control. Even randomized block design refers to the randomization occurring within the groups of similar experimental units called blocks.