Editing Survey methodology (section)

==Overview==
A single survey is made of at least a sample (or full population in the case of a census), a method of data collection (e.g., a questionnaire) and individual questions or items that become data that can be analyzed statistically. A single survey may focus on different types of topics such as preferences (e.g., for a presidential candidate), opinions (e.g., should abortion be legal?), behavior (smoking and alcohol use), or factual information (e.g., income), depending on its purpose. Since [[survey research]] is almost always based on a sample of the population, the success of the research is dependent on the representativeness of the sample with respect to a target population of interest to the researcher. That target population can range from the general population of a given country to specific groups of people within that country, to a membership list of a professional organization, or list of students enrolled in a school system  (see also [[sampling (statistics)]] and [[survey sampling]]). The persons replying to a survey are called [[respondent]]s, and depending on the questions asked their answers may represent themselves as individuals, their households, employers, or other organization they represent.

Survey methodology as a scientific field seeks to identify principles about the sample design, data collection instruments, statistical adjustment of data, and data processing, and final data analysis that can create systematic and random survey errors. Survey errors are sometimes analyzed in connection with survey cost. Cost constraints are sometimes framed as improving quality within cost constraints, or alternatively, reducing costs for a fixed level of quality. Survey methodology is both a scientific field and a profession, meaning that some professionals in the field focus on survey errors empirically and others design surveys to reduce them. For survey designers, the task involves making a large set of decisions about thousands of individual features of a survey in order to improve it.<ref name="Groves 2004">
{{cite book
  |last1=Groves|first1=R.M.
  |last2=Fowler|first2=F. J.
  |last3=Couper|first3=M.P.
  |last4=Lepkowski|first4=J.M.
  |last5=Singer|first5=E.
  |last6=Tourangeau|first6=R.
  |year=2009
  |title=Survey Methodology
  |location=New Jersey|publisher=John Wiley & Sons
  |isbn=978-1-118-21134-2
}}</ref>

The most important methodological challenges of a survey methodologist include making decisions on how to:<ref name="Groves 2004"/>
* Identify and select potential sample members.
* Contact sampled individuals and collect data from those who are hard to reach (or reluctant to respond)
* Evaluate and test questions.
* Select the mode for posing questions and collecting responses.
* Train and supervise interviewers (if they are involved).
* Check data files for accuracy and internal consistency.
* Adjust survey estimates to correct for identified errors.
* Complement survey data with new data sources (if appropriate)