Final answer:
The only research design that can determine cause-and-effect is the experimental design, specifically randomized controlled trials. These are not always used due to ethical, practical, or feasibility concerns. Observational studies offer insights when experimentation is not possible, but cannot establish causality.
Step-by-step explanation:
Explanation of Research Designs
The only type of research design that can provide cause-and-effect findings is an experimental design, particularly a randomized controlled trial. This approach is not used for all research questions due to a variety of constraints. For example, ethical considerations prevent researchers from exposing participants to potential harm, as would be the case in forcibly exposing individuals to tobacco to study the effects on lung cancer. Moreover, experimental designs can be more expensive and less feasible to conduct, especially with large populations or where the environment cannot be controlled. Observational studies, on the other hand, while unable to establish causation, can still provide valuable insights. They are often used when experimental studies are not practical, ethical, or possible.
An example of a study where a randomized experiment is not possible is examining the effects of birth order on personality. Here, the main difficulty is the inability to randomly assign birth order, thus making a randomized controlled trial impractical. Generally, studies lacking experimental design cannot control for all confounding variables, making it difficult to ascertain cause-and-effect relationships.
Strengths and Limitations of Research Methods
Each research method, including experimental and observational studies, has its own strengths and weaknesses, determined by the research question at hand. Experimental studies allow for claims of causation by manipulating variables under controlled conditions, while observational methods often rely on naturally occurring differences between subjects. The choice of research method impacts the generalizability, control, and ethical feasibility of the study.