Research Study Designs

Observational studies

Observes populations under prevailing conditions with no changes in conditions

Longitudinal study

Type of Observational Study that follows large groups over time to compare outcomes.

Cohort study

Compares exposed vs non exposed groups regarding variables.

Pros of Longitudinal (Cohort) Studies

Measures multiple outcomes, can look at multiple exposures, exposure is measured before the onset of disease (in prospective cohort studies), good for measuring rare exposures, demonstrate direction of causality, and can measure incidence and prevalence.

Disadvantages of Longitudinal (Cohort) Studies

Costly, time consuming, prone to bias due to loss to follow up, prone to confounding, participants may move between exposure categories, knowledge of exposure status may bias classification of the outcome, being in the study may alter participants' behavior, is a poor choice for the study of a rare disease, and classification of individuals (exposure or outcome status) can be affected by changes in diagnostic procedures.

Retrospective study

A type of Observational Study that looks back in time to measure past exposures.

Case control study

Type of Restrospective Study that compares two groups of people, those with cases and those without, to examine and measure exposures that could account for a disease

Advantages of case control studies

Cost effective, no long follow up, examines multiple exposures, and good for studying rare diseases or diseases with long latency periods

Disadvantages of case control studies

Prone to recall bias, limited to one outcome, typically can't examine incidence rates, and can't work when the exposure is rare.

Cross sectional study

Observational study at one point in time.

Advantages of cross sectional studies

Relatively quick and easy to conduct (no long periods of follow up), data on all variables is only collected once, able to measure prevalence for all factors under investigation, multiple outcomes and exposures can be studied, , good for descriptive analyses and for generating hypotheses

Disadvantages of cross sectional studies

Difficult to determine whether the outcome followed exposure in time or exposure resulted from the outcome, not suitable for studying rare diseases or diseases with a short duration, as cross sectional studies measure prevalent rather than incident cases, unable to measure incidence, associations identified may be difficult to interpret, susceptible to bias due to low response and misclassification due to recall bias.

Causal Design

assess whether an independent variable causes change in a dependent variable

Quasi experimental design

Type of Causal Design that has a control group but no random assignment (some precision and control)

Experimental Design

Type of Causal Design that has randomly assigned control trials (most precise design)

Randomized Clinical Trial

Type of Experimental Design that use clinical interventions and minimizes bias and provides evidence for causation.

P value

Probability indicating likelihood of chance results.

Low p value

Suggests significant results unlikely due to chance.

Pros of Observation Studies

Ethical and feasible, cost effective, real world applicability, good for hypothesis generation, and can study long term effects

Cons of Observation Studies

Not suitable for assessing causality due to non random assignment and variables can't be controlled, leading to bias in results

Pros of Randomized Clinical Trials

Provides the strongest evidence for causality, effectively control for confounding through randomization, ensure a clear temporal sequence, support strong statistical inference, minimize bias through blinding, and allow measurement of disease incidence and multiple outcomes

Cons of Randomized Clinical Trials

Ethical constraints, expensive and time consuming, requires complex design and analysis if allocation is not at the individual level, inefficient for rare or delayed outcome diseases, and limited generalizability due to selective participant compliance