3.3: Time Dimensions
- Page ID
- 124455
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- Define cross-sectional time frame, provide an example of a cross-sectional time frame, and outline some of the drawbacks of cross-sectional research.
- Describe the various types of longitudinal time dimensions.
Cross-Sectional Studies
In terms of time, there are two main types of studies: cross-sectional and longitudinal. Cross-sectional studies are those that are administered at just one point in time. These offer researchers a snapshot in time and give us an idea about how things are for our respondents at the particular moment that the study is administered.
An excellent example of a cross-sectional study comes from the Pew Research Center (2025), which examined American attitudes toward AI. These researchers administered a single, one-time cross-sectional survey to U.S. adults. The researchers found from the analysis of their cross-sectional data that 53% of Americans feel AI will worsen creativity. Because this was a cross-sectional study, that statistic represents a snapshot of societal anxiety frozen exactly in 2025.
One major problem with cross-sectional studies is that the events, opinions, behaviors, and other phenomena they assess do not generally remain stagnant. Generalizing from a cross-sectional study about "the way things are" can be tricky; you can say something about the way things were in the exact moment you administered your study, but it is difficult to know if things remained that way. Think, for example, about how college students might have responded to a cross-sectional survey about using Artificial Intelligence to help write their essays in October 2022. Now imagine how responses to the exact same questions would differ just three months later in January 2023, immediately following the public release and viral explosion of ChatGPT. The point is not that cross-sectional studies are useless—they have many important applications. But researchers must remember what they have captured: a snapshot of life as it was at the exact time the study was administered.
One way to overcome this snapshot limitation is to conduct a longitudinal study. Longitudinal studies are those that enable a researcher to make observations over some extended period of time. There are several types of longitudinal studies, including trend, panel, and cohort studies.
Longitudinal Studies
1. Trend Study
2. Panel Study
3. Cohort Study
Summary
| Sample type | Description |
|---|---|
| Trend Study | The researcher examines changes in trends over time; a new sample is done each time. |
| Panel Study | Researchers study the exact same sample of individuals several times over an extended period. |
| Cohort Study | The researcher identifies a category of people who share a defining trait (e.g., a generation) and tracks that category over time. |
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Cross-Sectional Studies: Research administered at only one point in time, providing a snapshot.
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Trend Studies: Examine shifts in general populations over time using different respondents.
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Panel Studies: Track the exact same individuals over an extended period.
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Cohort Studies: Track a specific subpopulation (like a birth generation) over time.