Final answer:
Inclusion and exclusion criteria are defined in the study protocol to ensure a homogeneous study population and applicable results. Human experiments are common and regulated, and larger sample sizes are preferred for statistical significance. However, there are challenges associated with experiments, including maintaining control and test group comparability.
Step-by-step explanation:
Inclusion and exclusion criteria are indeed defined in the study protocol. These criteria are a set of guidelines outlining who can or cannot participate in a research study. Defining these parameters ensures that the study population is fairly homogeneous and that the results are applicable to the population that the research is meant to serve. It also minimizes variability and helps ensure participant safety.
For instance, a clinical trial might include criteria based on age, sex, the stage of a disease, previous treatment history, and other medical conditions to ensure the study results can be generalized to a specific group. Experiments on humans are possible and indeed very common in the scientific and medical fields, although they are highly regulated to ensure ethical treatment and safety of participants.
It is also acknowledged that while larger sample sizes in scientific experiments are generally favorable, as they can provide more statistically significant results and reduce the impact of outliers, they must be balanced with the practicalities of conducting a study, including cost and time constraints. Lastly, while experiments can identify cause-and-effect relationships, there are challenges associated with them such as ensuring the control group and test group are identical except for the variable under study, among others.