Design of Experiments > Data Collection Methods
Data Collection Methods: General Categories
Data collection methods fall into four general categories:
- A census is a survey of a whole population. For example, the U.S. Census. Censuses can be very expensive and time-consuming, if the population is large.
- A sample survey takes a fraction of the population. Sample surveys are cheaper than censuses, but are not as accurate. Bias can also be an issue.
- An experiment is a controlled study of a group. Experiments are very common in the medical fields. The researcher controls how members are placed study groups and which treatment each group receives. Bias can be a major issue with experiments.
- An observational study is about the same as an experiment. However, the researcher does not use control groups or assign treatments.
What is the best of the Data Collection Methods?
There is no one “best” data collection method. Each method has its pros and cons. Which one you choose depends on what kind of data you have (i.e. qualitative data or quantitative data) and which pros/cons are important for your study.
In general, the following data collection methods work for qualitative research:
- Document review.
- In depth interviews.
- Observation methods.
Quantitative research data collection methods, which tends to rely on random samples, include:
- Surveys with closed-ended questions.
- Clinical trials/experiments.
- Extracting data from computer and information systems.
- Observing, counting and recording events that are well defined (for example, counting the number of people who come into a restaurant).
Types of Data Collection Methods
- Interviews are very structured for quantitative research. They are less structured for qualitative research. In a structured interview, you would asks= a series of standard questions; in less-structured interview you might ask open-ended questions.
- Face-to-face interviews can be time-consuming and expensive. However, you can establish rapport with an interviewee and may have the opportunity to clarify responses. Face-to-face interviews have a very high response rate.
- Telephone Interviews are cost-effective and take less time than face-to-face interviews. However, the response rate isn’t as high. Another con is that survey bias may creep in. For example, people without phones can’t be surveyed.
- Computer Assisted Personal Interviewing (CAPI) is like a personal interview, but you bring a laptop or tablet instead of paper questionnaires to enter the responses. CAPI has the same drawbacks as face-to-face interviews
- Questionnaires
- Paper and pencil questionnaires can be sent to a large group of people. They have the advantage of respondents tending to be more truthful with responses. A disadvantage is a very low response rate.
- Internet questionnaires are cheaper and faster than paper questionnaires. But they exclude people who do not have access to computers. In addition, people tend to hurry to complete internet surveys so the responses may not be valid.