Descriptive Research
Descriptive research is a study designed to depict the participants in an accurate way. More simply put, descriptive analysis is all about describing people who take part in the survey.
There are three ways a researcher can go about doing a descriptive research project, and they are:

Observational, defined as a method of viewing and recording the participants
Case study, defined as an in-depth study of an individual or group of individuals
Survey, defined as a brief interview or discussion with an individual about a specific topic

Descriptive Blog: The 3 Basic Types of Descriptive Research Methods
https://psychcentral.com/blog/the-3-basic-types-of-descriptive-research-methods/
Video: Descriptive Research Design

Mixed Methods Research
Mixed methods research (Extracted from the article below) is the use of quantitative and qualitative methods in a single study or series of studies. It is a new methodology that is increasingly used by health researchers, especially within health services research. There is a growing literature on the theory, design, and critical appraisal of mixed methods research. However, few papers summarize this methodological approach for health practitioners who wish to conduct or critically engage with mixed methods studies.
Article: Using Mixed Methods in Health Research
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3697857/
Mixed Methods

Meta-Analysis
Meta-analysis is a statistical technique for combining data from multiple studies on a particular topic. A Meta-analysis is an analytical tool for estimating the mean and variance of underlying population effects from a collection of empirical studies addressing ostensibly the same research question. Meta?analysis has become an increasingly popular and valuable tool in psychological research, and significant review articles typically employ these methods.
Article: Meta-Analysis in Medical Research
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3049418/
Video Meta-Analysis (An Introduction)

Epidemiology
According to the Centers for Disease Control, Epidemiology is the method used to find the causes of health outcomes and diseases in populations. In epidemiology, the patient is the community and individuals are viewed collectively. By definition, epidemiology is the study (scientific, systematic, and data-driven) of the distribution (frequency, pattern) and determinants (causes, risk factors) of health-related states and events (not just diseases) in specified populations (neighborhood, school, city, state, country, global).
Article: Epidemiology is a Science of High Importance
https://www.nature.com/articles/s41467-018-04243-3.pdf
Video: Epidemiology

Longitudinal Studies
Longitudinal Study, an epidemiologic study that follows a population forward over time, evaluating the effects of one or more variables on a process. If individuals are followed, it is termed a longitudinal cohort study. If classes—e.g., age classes—are studied, it is a longitudinal cross-sectional study. Longitudinal studies are the converse (opposite) of horizontal (parallel) studies.
Article Longitudinal Studies
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4669300/
Video (A Lecture Recording): Longitudinal Studies