Hello anjali,
For research methodology for entrancd exams for statistics and i refer you ayurveda 'phd entrance guide' written by Dr. Sanjay patil and Dr. Varsharani patil.
Its available on amazon and various sites for ruppess 399.
https://www.amazon.in/dp/B081XP5L3S
All the best for your exam anjali.

Hi Anjali ! you can use these books for Phd entrance exam :

1) Research Design: Qualitative, Quantitative, and Mixed Methods Approaches by John W. Creswell and J. David Creswell

2)Qualitative Research: A Guide to Design and Implementation by Sharan B. Merriam

3) Research Justice by Andrew J Jolivette

4) Introducing Research Methodology: A Beginner′s Guide to Doing a Research Project by Uwe Flick

5) Introduction to Quantitative Research Methods: An Investigative Approach by Mark Balnaves & Peter Caput

Hope this will help you.

Thank you so Much.