The differentiating characteristic between observational and experimental study designs is that in the latter, the presence or absence of undergoing an intervention defines the groups.
Observational study For observational study the main types will then depend on the timing of the measurement of outcome, so our third question is: Observational studies investigate and record exposures such as interventions or risk factors and observe outcomes such as disease as they occur.
In this review article, we describe these study designs, methodological issues, and provide examples from the plastic surgery literature. Results from observational studies are often criticized for being vulnerable to influences by unpredictable confounding factors.
Abstract Observational studies are an important category of study designs.
An analytic study attempts to quantify the relationship between two factors, that is, the effect of an intervention I or exposure E on an outcome O. For example, a the control arm of a randomised trial may also be used as a cohort study; and the baseline measures of a cohort study may be used as a cross-sectional study.
Whether the researcher actively changes a factor or imposes uses an intervention determines whether the study is considered to be observational passive involvement of researcheror experimental active involvement of researcher.
Tree of different types of studies Q1, 2, and 3 refer to the three questions below Download a PDF by Case control study level of evidence Howick about Study Designs Our first distinction is whether the study is analytic or non-analytic.
These studies all include matched groups of subjects and assess of associations between exposures and outcomes. That is, subjects are allocated to two or more groups to receive an intervention or exposure and then followed up under carefully controlled conditions.
We should finally note that studies can incorporate several design elements. Cohort studies and case-control studies are two primary types of observational studies that aid in evaluating associations between diseases and exposures.
Some time after the exposure or intervention? Cross-sectional studies, also known as prevalence studies, examine the data on disease and exposure at one particular time point Figure 2.
Such studies controlled trials, particularly if randomised and blinded, have the potential to control for most of the biases that can occur in scientific studies but whether this actually occurs depends on the quality of the study design and implementation.
However, recent work has challenged this notion, showing comparable results between observational studies and RCTs.
In analytic observational studies, the researcher simply measures the exposure or treatments of the groups. Descriptive studies include case reports, case-series, qualitative studies and surveys cross-sectional studies, which measure the frequency of several factors, and hence the size of the problem.
Such studies may be purely descriptive or more analytical. To quantify the effect we will need to know the rate of outcomes in a comparison C group as well as the intervention or exposed group. A defined population P from which groups of subjects are studied Outcomes O that are measured And for experimental and analytic observational studies: To address some investigative questions in plastic surgery, randomized controlled trials are not always indicated or ethical to conduct.
Spotting the Study Design The type of study can generally be worked at by looking at three issues as per the Tree of design in Figure 1: Interventions I or exposures E that are applied to different groups of subjects Overview of the design tree Figure 1 shows the tree of possible designs, branching into subgroups of study designs by whether the studies are descriptive or analytic and by whether the analytic studies are experimental or observational.
When were the outcomes determined? The list is not completely exhaustive but covers most basics designs. Observational studies fall under the category of analytic study designs and are further sub-classified as observational or experimental study designs Figure 1.
The goal of analytic studies is to identify and evaluate causes or risk factors of diseases or health-related events. In experimental studies, the researcher manipulates the exposure, that is he or she allocates subjects to the intervention or exposure group.
What was the aim of the study? Experimental studies, or randomised controlled trials RCTsare similar to experiments in other areas of science. If analytic, was the intervention randomly allocated? Well-designed observational studies have been shown to provide results similar to randomized controlled trials, challenging the belief that observational studies are second-rate.• Level II (a): Good studies with a non-randomized control group (case/control or cohort).
Prospective data or case notes, similar groups, correcting for confounding in the analysis, • Level II (b): Poor studies with a non-randomized control group (case/control or cohort). See also Levels of Evidence. These study designs all have similar components (as we’d expect from the PICO): A defined population (P) from which groups of subjects are studied; Analytical observational studies include case””control studies, cohort studies and some population (cross-sectional) studies.
Level IV: Evidence from well-designed case-control and cohort studies Level V: Evidence from systematic reviews of descriptive and qualitative studies Level VI: Evidence from a single descriptive or qualitative study. Also: cohort study, case-control study, case series.
Etiology. Randomized controlled trial (RCT), meta-analysis, cohort study Also: case-control study, case series. Diagnosis. The Johns Hopkins Nursing EBP Evidence Level and Quality Guide is provided via the link below. Cohort studies and case-control studies are two primary types of observational studies that aid in evaluating associations between diseases and exposures.
In this review article, we describe these study designs, methodological issues, and provide examples from the plastic surgery literature.
spective comparative study; study of nonconsecutive patients without consistently applied reference “gold” standard; analyses based on limited alternatives and costs and poor estimates; sys-tematic review of Level III studies. Level IV: Case series; case control study (diagnostic studies); poor refer-ence standard; analyses with no sensitivity .Download