Sociologists use many different designs and methods to study society and social behavior. Most sociological research involves ethnography, or “field work” designed to depict the characteristics of a population as fully as possible. Three popular social research designs (models) are Cross‐sectional, in which scientists study a number of individuals of different ages who have the same trait or characteristic of interest at a single time Longitudinal, in which scientists study the same individuals or society repeatedly over a specified period of time Cross‐sequential, in which scientists test individuals in a cross‐sectional sample more than once over a specified period of time Six of the most popular sociological research methods (procedures) are the case study, survey, observational, correlational, experimental, and cross‐cultural methods, as well as working with information already available. Case study research In case study research, an investigator studies an individual or small group of individuals with an unusual condition or situation. Case studies are typically clinical in scope. The investigator (often a clinical sociologist) sometimes uses self‐report measures to acquire quantifiable data on the subject. A comprehensive case study, including a long‐term follow‐up, can last months or years. On the positive side, case studies obtain useful information about individuals and small groups. On the negative side, they tend to apply only to individuals with similar characteristics rather than to the general population. The high likelihood of the investigator's biases affecting subjects' responses limits the generalizability of this method. Survey research Survey research involves interviewing or administering questionnaires, or written surveys, to large numbers of people. The investigator analyzes the data obtained from surveys to learn about similarities, differences, and trends. He or she then makes predictions about the population being studied. As with most research methods, survey research brings both advantages and disadvantages. Advantages include obtaining information from a large number of respondents, conducting personal interviews at a time convenient for respondents, and acquiring data as inexpensively as possible. “Mail‐in” surveys have the added advantage of ensuring anonymity and thus prompting respondents to answer questions truthfully. Disadvantages of survey research include volunteer bias, interviewer bias, and distortion. Volunteer bias occurs when a sample of volunteers is not representative of the general population. Subjects who are willing to talk about certain topics may answer surveys differently than those who are not willing to talk. Interviewer bias occurs when an interviewer's expectations or insignificant gestures (for example, frowning or smiling) inadvertently influence a subject's responses one way or the other. Distortion occurs when a subject does not respond to questions honestly. Observational research Because distortion can be a serious limitation of surveys, observational research involves directly observing subjects' reactions, either in a laboratory (called laboratory observation) or in a natural setting (called naturalistic observation). Observational research reduces the possibility that subjects will not give totally honest accounts of the experiences, not take the study seriously, fail to remember, or feel embarrassed. Observational research has limitations, however. Subject bias is common, because volunteer subjects may not be representative of the general public. Individuals who agree to observation and monitoring may function differently than those who do not. They may also function differently in a laboratory setting than they do in other settings. Correlational research A sociologist may also conduct correlational research. A correlation is a relationship between two variables (or “factors that change”). These factors can be characteristics, attitudes, behaviors, or events. Correlational research attempts to determine if a relationship exists between the two variables, and the degree of that relationship. A social researcher can use case studies, surveys, interviews, and observational research to discover correlations. Correlations are either positive (to +1.0), negative (to −1.0), or nonexistent (0.0). In a positive correlation, the values of the variables increase or decrease (“co‐vary”) together. In a negative correlation, one variable increases as the other decreases. In a nonexistent correlation, no relationship exists between the variables. People commonly confuse correlation with causation. Correlational data do not indicate cause‐and‐effect relationships. When a correlation exists, changes in the value of one variable reflect changes in the value of the other. The correlation does not imply that one variable causes the other, only that both variables somehow relate to one another. To study the effects that variables have on each other, an investigator must conduct an experiment. Experimental research Experimental research attempts to determine how and why something happens. Experimental research tests the way in which an independent variable (the factor that the scientist manipulates) affects a dependent variable (the factor that the scientist observes). A number of factors can affect the outcome of any type of experimental research. One is finding samples that are random and representative of the population being studied. Another is experimenter bias, in which the researcher's expectations about what should or should not happen in the study sway the results. Still another is controlling for extraneous variables, such as room temperature or noise level, that may interfere with the results of the experiment. Only when the experimenter carefully controls for extraneous variables can she or he draw valid conclusions about the effects of specific variables on other variables. Cross-cultural research Sensitivity to others' norms, folkways, values, mores, attitudes, customs, and practices necessitates knowledge of other societies and cultures. Sociologists may conduct cross‐cultural research, or research designed to reveal variations across different groups of people. Most cross‐cultural research involves survey, direct observation, and participant observation methods of research. Participant observation requires that an “observer” become a member of his or her subjects' community. An advantage of this method of research is the opportunity it provides to study what actually occurs within a community, and then consider that information within the political, economic, social, and religious systems of that community. Cross‐cultural research demonstrates that Western cultural standards do not necessarily apply to other societies. What may be “normal” or acceptable for one group may be “abnormal” or unacceptable for another. Research with existing data, or secondary analysis Some sociologists conduct research by using data that other social scientists have already collected. The use of publicly accessible information is known as secondary analysis, and is most common in situations in which collecting new data is impractical or unnecessary. Sociologists may obtain statistical data for analysis from businesses, academic institutions, and governmental agencies, to name only a few sources. Or they may use historical or library information to generate their hypotheses.