5.5: Types of Research Studies - Ecological and Case-Control Studies
- Page ID
- 103657
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The two general types of research studies are either observational or experimental. Observational studies come in many forms, but the researcher is always recording and analyzing information on the subjects - never interfering in any way. This differs from an experimental study, in which the researcher’s primary goal is to determine whether a specific intervention causes a measurable outcome or not. Observational studies include ecological, cross-sectional, case-control and cohort (or longitudinal) studies. Experimental studies are often referred to as clinical trials, or randomized controlled trials (RCTs).
Ecological studies are very basic statistical analyses of incidence or prevalence of some disease, risk factor or protective factor within a population or group. These types of studies are helpful in identifying a potentially vulnerable population, and/or the need for more research for particular risk factors. A hypothetical ecological study might find that counties with more office workers also had higher rates of back pain. We couldn’t conclude any causation from this type of study though. It could be that office work causes back pain, or it could be that people with back pain change careers so that they can work in an office, or it could be that office workers have better healthcare plans and therefore go to the doctor more often for musculoskeletal issues like back pain… there could be many indirect ways these two things are associated, or there could be no association at all. What if the people who had back pain aren’t also those who work in offices? Ecological studies are helpful at generating ideas for populations of interest or possible relationships between risks or protective factors and health outcomes. See Fig 5.2 for a diagram of ecological studies.
Cross-sectional studies are those that take a snapshot of a population at one point in time. This can be imagined similarly to a cross-sectional view of a limb in anatomy; it’s almost like you’re taking a “slice” of the population and looking at their current prevalence of specific risks or protective factors and health outcomes. A lot of times we may want to do a cross-sectional study to identify a specific need in a population. For example, we might do a cross-sectional study to identify how many office workers in a particular area currently have low back pain. Perhaps we survey these workers or offer a screening at each office location. The difference between an ecological study and a cross-sectional study is that the ecological studylooks at prevalence statistics in groups, whereas a cross-sectional study uses individual data - so in our own hypothetical example we can be sure whether it’s the office workers who have the low back pain. See Fig 5.3 for a diagram of cross-sectional studies.
