Quantitative data collection methods typically use standardized response categories. Surveys are the most common example. Respondents are asked to choose among responses that best characterize their perceptions, attitudes, knowledge, or opinions. The advantage of quantitative data is that it efficiently measures the reactions of many people which facilitates statistical aggregation of the data, including making comparisons by subgroups. Using sound sampling procedures to represent the population and obtaining adequate response rates are critical. Provided your sample size is large enough, and your methods and analysis are sound, this method of data collection provides a broad, generalizable set of findings. This means that they can be used to learn about the entire population that you are studying.
By contrast, qualitative data collection methods typically produce detailed data about a much smaller number of people. Qualitative data can provide rich information through direct quotation and careful description of programs, events, people, interactions, and observed behaviors. The advantage and disadvantage of such descriptions, quotations, and case studies is that they are collected as open-ended narratives. Observations are not fit to categories so rigorous and systematic analysis of content can be tedious and time-consuming.
One of the most common qualitative data collection techniques is the interview which may be with individuals or a group. In a group interview, or focus group, a moderator conducts a discussion among five to ten people in order to learn their opinions, attitudes, and thought processes about a given topic. The group dynamic encourages a deeper level of discussion and allows the moderator to probe for topics that are important. Note that the term focus group is often misused to refer to any meeting of any group of people about a given topic. In actuality, focus groups as well as individual interviews, are systemically structured and discussion is carefully guided to allow for drawing conclusions and making comparisons. Qualitative data can also be collected from written sources such as journals, open-ended survey questions, and reaction sheets completed by observers or participants.
An ethnographic approach to evaluation collects qualitative data. Maribel Alvarez describes in her case study, Two-Way Mirror: Ethnography as a Way to Assess Civic Impact of Arts-based Engagement in Tucson, AZ, that ethnographic evaluation emphasizes listening carefully and observing real-life actions to understand how people make sense of their lives. An ethnographic evaluation produces “data collection” of a distinct kind—subjective accounts of how people actually interact with systems, programs, and policies. This data is collected through experiences of the evaluator in the field, side by side with participants.