BUKU METOPEN Ebook Metopen
https://repository.dinus.ac.id/docs/ajar/Kothari_-
_Research_Methodology_Methods_and_Techniques_-_2004.pdf
https://mfs.mkcl.org/images/ebook/Fundamental%20of%20Research%20Methodology%20a nd%20Statistics%20by%20Yogesh%20Kumar%20Singh.pdf
https://digilib.politeknik-
pratama.ac.id/assets/dokumen/ebook/feb_f006f52b62a646e28c8c7870aa1112fbcd0c49ca_
1650455622.pdf
https://www.euacademic.org/BookUpload/9.pdf
https://kosalmath.wordpress.com/wp-content/uploads/2010/08/introduction-to-research- methods.pdf