Identifying Major Research Designs

Research designs are frameworks used to conduct research. Several types are considered major categories:

• Experimental Designs: These involve manipulating variables to determine cause-and-effect relationships. They often include control groups and random assignment.
• Cross-sectional Designs: Data is collected from a population, or a representative subset, at one specific point in time. It's useful for understanding prevalence or comparing different groups at a single moment.
• Longitudinal Designs: These involve repeatedly observing or collecting data from the same subjects over a period of time. This allows for the study of changes, trends, or developments.
• Case-study Designs: An in-depth investigation of a single individual, group, event, or community. It provides detailed qualitative insights into a specific phenomenon.

All the listed designs (Experimental, Cross-sectional, Longitudinal, and Case-study) are widely recognized and utilized as major research methodologies across various fields.

Therefore, all options A, B, C, and D are included in major research designs.

Final Answer Determination

Based on the established categories of major research designs:

• Experimental design is a major type.
• Cross-sectional design is a major type.
• Longitudinal design is a major type.
• Case-study design is a major type.

Since all four are considered major research designs, the correct option includes A, B, C, and D.