Q: In research, what is the difference between the rationale and the justification of a study?

Answer: Actually, there is no difference between the rationale and the justification of the study. If you're asked to include the rationale or justification of a study, you should clearly explain

1. What is the gap or controversy in existing knowledge
2. Why this gap or controversy is worth addressing
3. How your study will address this gap or controversy

  Here's a skeleton example of how you can present the rationale or justification of a study:   Although many previous studies have shown a relationship between serum LDL levels and altiventicular thrombosis in old-old adults, they have not controlled for Vitamin B15 intake, a known prognostic factor for altiventicular thrombosis in this population. We attempt to address this gap by ....   As the rationale/justification is written in the Introduction of the paper, you may find this handbook helpful: How to write a strong introduction section that makes a great first impression  

Answer: Actually, there is no difference between the rationale and the justification of the study. Both mean the same thing; the terms are used interchangeably. :-) You may learn more about the rationale/justification of research through these resources:

• Can you give an example of the "rationale of a study"?
• How to write the rationale for research?
• What is the justification of a research?

As the rationale/justification is written in the Introduction of the paper, you may find this handbook helpful: How to write a strong introduction section that makes a great first impression Hope that helps!