Office of the Secretary (1979). The Belmont Report. This link will take you to the original Belmont Report that is a seminal document outlining ethical principles and guidelines on research involving human subjects.
Muijs, D. (2011). Doing quantitative research in education with SPSS. London: SAGE Publications, Inc. Chapter 1 introduces quantitative research. While the focus in this source is on education, the concepts discussed in this source apply to any industry or field leveraging quantitative research methods. This source provides a very succinct and consumable introduction to quantitative research.
Arghode, V. (2012). Qualitative and Quantitative Research: Paradigmatic Differences. Global Education Journal, 2012(4), 155–163. This resource compares and contrasts qualitative and quantitative research with regard to their underlying assumptions, as well as epistemological, ontological, and methodological differences.