Editing Survey methodology (section)

==Research designs==
There are several different designs, or overall structures, that can be used in survey research. The three general types are cross-sectional, successive independent samples, and longitudinal studies.<ref name="Shaughnessy2011"/>

===Cross-sectional studies===
In cross-sectional studies, a sample (or samples) is drawn from the relevant population and studied once.<ref name="Shaughnessy2011"/> A cross-sectional study describes characteristics of that population at one time, but cannot give any insight as to the causes of population characteristics because it is a predictive, correlational design.

===Successive independent samples studies===
A successive independent samples design draws multiple random samples from a population at one or more times.<ref name="Shaughnessy2011"/>  This design can study changes within a population, but not changes within individuals because the same individuals are not surveyed more than once. Such studies cannot, therefore, identify the causes of change over time necessarily. For successive independent samples designs to be effective, the samples must be drawn from the same population, and must be equally representative of it. If the samples are not comparable, the changes between samples may be due to demographic characteristics rather than time. In addition, the questions must be asked in the same way so that responses can be compared directly.

===Longitudinal studies===
Longitudinal studies take measure of the same random sample at multiple time points.<ref name="Shaughnessy2011"/>  Unlike with a successive independent samples design, this design measures the differences in individual participants' responses over time. This means that a researcher can potentially assess the reasons for response changes by assessing the differences in respondents' experiences. Longitudinal studies are the easiest way to assess the effect of a naturally occurring event, such as divorce that cannot be tested experimentally.

However, longitudinal studies are both expensive and difficult to do. It is harder to find a sample that will commit to a months- or years-long study than a 15-minute interview, and participants frequently leave the study before the final assessment. In addition, such studies sometimes require data collection to be confidential or anonymous, which creates additional difficulty in linking participants' responses over time. One potential solution is the use of a self-generated identification code (SGIC).<ref>{{Cite journal|last1=Audette|first1=Lillian M.|last2=Hammond|first2=Marie S.|last3=Rochester|first3=Natalie K.|date=February 2020|title=Methodological Issues With Coding Participants in Anonymous Psychological Longitudinal Studies|journal=Educational and Psychological Measurement|language=en|volume=80|issue=1|pages=163–185|doi=10.1177/0013164419843576|issn=0013-1644|pmc=6943988|pmid=31933497}}</ref> These codes usually are created from elements like 'month of birth' and 'first letter of the mother's middle name.' Some recent anonymous SGIC approaches have also attempted to minimize use of personalized data even further, instead using questions like 'name of your first pet.<ref>{{Cite journal|last1=Agley|first1=Jon|last2=Tidd|first2=David|last3=Jun|first3=Mikyoung|last4=Eldridge|first4=Lori|last5=Xiao|first5=Yunyu|last6=Sussman|first6=Steve|last7=Jayawardene|first7=Wasantha|last8=Agley|first8=Daniel|last9=Gassman|first9=Ruth|last10=Dickinson|first10=Stephanie L.|date=February 2021|title=Developing and Validating a Novel Anonymous Method for Matching Longitudinal School-Based Data|journal=Educational and Psychological Measurement|language=en|volume=81|issue=1|pages=90–109|doi=10.1177/0013164420938457|issn=0013-1644|pmc=7797962|pmid=33456063}}</ref><ref>{{Cite journal|last1=Calatrava|first1=Maria|last2=de Irala|first2=Jokin|last3=Osorio|first3=Alfonso|last4=Benítez|first4=Edgar|last5=Lopez-del Burgo|first5=Cristina|date=2021-08-12|title=Matched and Fully Private? A New Self-Generated Identification Code for School-Based Cohort Studies to Increase Perceived Anonymity|url=https://doi.org/10.1177/00131644211035436|journal=Educational and Psychological Measurement|volume=82 |issue=3 |language=en|pages=465–481|doi=10.1177/00131644211035436|pmid=35444340 |pmc=9014735 |s2cid=238718313|issn=0013-1644}}</ref>  Depending on the approach used, the ability to match some portion of the sample can be lost.

In addition, the overall attrition of participants is not random, so samples can become less representative with successive assessments. To account for this, a researcher can compare the respondents who left the survey to those that did not, to see if they are statistically different populations. Respondents may also try to be self-consistent in spite of changes to survey answers.