What type of research does not allow for random assignment of participants?

Non-experimental research is characterized by the absence of random assignment of participants to different groups or conditions. This type of research is often used when it is impractical or unethical to manipulate variables or randomly assign subjects. For example, studies that observe natural variations or correlations in behavior without intervention fall into this category.

In contrast, experimental research involves manipulated variables and the random assignment of participants, allowing researchers to establish cause-and-effect relationships. Quantitative research focuses on numerical data and statistical analysis but can include both experimental and non-experimental designs. Qualitative research emphasizes understanding underlying reasons and motivations, often through non-numerical data, and does not typically involve random assignment or controlled experiments. Thus, non-experimental research is the correct response as it inherently lacks the feature of random assignment.