Listed below are a small sampling of a few methods that researchers use in their work.
Experiments - an experiment normally involves the randomized allocation of cases to experimental and control groups, exposing only the experimental group to a treatment whilst controlling the influence of extraneous factors.
Surveys (or Questionnaires) - a set of carefully designed questions given in exactly the same form to a group of people in order to collect data about some topic(s) in which the researcher is interested.
Participant Observation - a qualitative method of social investigation, whereby the researcher participates in the everyday life of a social setting, and records their experiences and observations.
Ethnography - a research method that includes participant observation, interviews, conversational and discourse analysis, documentary analysis, film and photography, and life histories.
Interviews - a method of data collection, information or opinion gathering that specifically involves asking a series of questions.
Archival Research - primary source research that makes use of evidence found in archival records.
Discourse Analysis - detailed exploration of political, personal, media or academic ‘talk’ and ‘writing’ about a subject, designed to reveal how knowledges are organized, carried and reproduced in particular ways and through particular institutional practices.
Secondary Data - the further analysis of an existing data set with the aim of addressing a research question distinct from that for which the data set was originally collected, and generating novel interpretations and conclusions.
Spatial Statistics - the exploration of physical and spatial features of a particular environment which are associated with certain social outcomes, such as social exclusion or crime, and are therefore seen as having a contributory or perhaps causal effect on social processes or social phenomena.
Source: Victor Jupp, The SAGE Dictionary of Social Research Methods, 2006