Principles are the fundamental assumptions. There are some fundamental assumptions in the selection of research design which are given below:

1. Principle of flexibility: Research design should be flexible enough. A researcher may need to improve the design while conducting research because the researcher may face the problem in the real field. To address such problems, the researcher needs to change in design. Thus, the research design should be flexible.

2. Principle of timeliness: Research design should specify the time so that every activity can be completed in time and the researcher can produce a research report in time.

3. Principle of replication: Research design that is used by one researcher should be replicable (can be copied) to others whoever likes to do so. It helps to test the design in the different context and helps to theorize the findings.

4. Principle of objective: Research design should be developed in such a way so that it gives the results in a specific and clear form. The results of the research should not be emotional and subjective.

5. Principle of generalizability: research design is to be developed in such a way that the findings developed from the research can be generalized in the large population even though the findings are developed from the study of the sample.

6. Principle of reliability: Research design depends on reliability, consistencies, dependability, and stability. If research gives the same result when same tools are used in the same sample, then such research is considered as reliable research. Research design should be developed in such a way so that it gives consistent results.

7. Validity: Validity is concerned with the integrity of the conclusions that are generated from a piece of research. Research design should specify the variables that can measure the things that they want to measure.