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Most Nonexperimental designs can describe behaviors, but cannot explain behaviors, and are used in situations in which an experiment is not practical or desirable (Myers, & Hansen, 2012). There are, however, both advantages and disadvantages to each approach: 
 Naturalistic observation is a descriptive method of study where one observes behavior as it happens naturally (Myers, & Hansen, 2012). This approach is often used in studies of animals in the wild and in captivity. When observing animals in their natural habitat, a difficult but important task is to try to stay hidden, as animals and humans cannot behave the same if they know they are being monitored. It is important not to alter behaviors by disrupting their habitat. Observing an animal or human in their natural habitat allows researchers the advantage of watching natural behaviors and actions unfold without any restrictions (Myers, & Hansen, 2012).  
Phenomenological studies focus on an individuals immediate experience and cannot be replicated. Since its primary focus is on our own experiences, it cannot be certain that the results are biased based on our individual focus on an experience (Myers, & Hansen, 2012). Typically, phenomenological when used is combined with other design approaches. One other disadvantage is that, like phenomenological studies, naturalistic observation cannot be replicated.  
Case studies require no manipulation as well; case study research is conducted by an observer on a real-life, behavior, or both (Myers, & Hansen, 2012). There are very few restrictions on information that can be used in a case study, and case studies are used frequently with forensic psychology and clinical psychology. Cases studies are known to have persuasive value and can provide exceptions to certain theories and practices. Case studies are great for researching rare disorders and can even be used to sell individuals of specific products (Myers, & Hansen, 2012). A couple of significant disadvantages in using case studies are the limited number of subjects involved in a case study, it may t be the best representation of the general population, and the use of retrospective data can be unreliable. 
Archival studies are the study of pulling a previous study and revaluating it for a different study (Myers, & Hansen, 2012). Some advantages to archival studies are the researcher does not have to worry about disrupting natural behaviors like in other approaches to nonexperimental designs, but there is not a guarantee that the previous research pulled to be utilized is accurate. The disadvantage of using archival research is that the data may not directly respond to the research question, so the data may have to be re-coded to answer a new question. 
Case studies are particularly interesting to me; if I had to choose no experimental design, I would choose case studies. They can be utilized to persuade new practices or procedures, for investigative purposes in multiple fields of study, and researchers can compare different case studies for differences that could infer advances in the psychology field. While there is no guarantee that each case study could be used to describe the general population, they can assess rare cases