1.3 Study Design Flashcards
What are the two broad categories for study designs?
Observational & Experimental
What are the two classes of Observational study designs?
Descriptive & Analytical
What are the two types of Descriptive studies?
Case-series & Ecological
What are the three types of Analytical studies?
Cross-Sectional
Case-Control
Cohort
What is the one type of Experimental study design?
Randomised Control Trial
Describe Case-Series, its measures and information and it’s limitations
Observational, Descriptive. Information: description.
Characteristics of several patients with a specific disease are described but are not compared with those of a reference population. Often leads to more detailed epidemiological study.
Limitations: selective sampling and limited information. Difficult to ascertain causality and patterns of disease occurrence
Describe Ecological studies, measure & information and their limitations
Observational & Descriptive. Population based. Outcome and exposure at same time. Measures: Prevalence, correlations between outcome and exposure at population level.
Units of analysis are groups rather than individuals (population based). Large-scale, easy, cheap. Can calculate prevalence.
Limitations: confounding factors, cannot ascertain causality
Describe Cross-Sectional studies, their measures & information as well as their advantages and limitations
Observational & Analytic. Sample representative of Population. Outcome and exposure at same time. i.e. no time frame on exposure then disease, but rather if the have been and exposed and if they have disease.
Measures: Prevalence; individual level –> identify possible risk factors.
Advantage: Good for hypothesis testing, can study multiple exposures, outcomes, and disease, cost effective
Limitations: Impractical for rare disease, cannot establish causal relationships, confounding difficult to control.
Describe Case-Control studies, their measure & information as well as their advantages and limitations
Observational & Analytic. Population based. Begins with selection of cases and controls then to go backwards in time and determine possible exposures.
Advantages: suitable for rare outcomes, cheaper, need fewer people in some cases, can evaluate multiple exposures.
Measures: Odds ration - odds of exposure causing outcome
Limitations: Does not directly estimate risk, cannot calculate prevalence, recall bias, studying survivors of disease, difficult to study rare exposures, controls need to be selected with care
Describe Cohort Studies, their advantages and their disadvantages
Observational, Analytic. Population based. Start with defined population (disease free) that either was or was not exposed and follow in time to determine outcome.
Measures: Incidence, rate ratios, risk of outcome as function of exposure
Advantages: able to directly estimate risk, optimal of short induction periods, multiple outcomes
Limitations: not suitable for rare exposure or rare outcomes, requires large populations, expensive & time consuming
Describe Randomised Control Trials, their advantages and disadvantages
Experimental, population based at individual level. Best practice for evaluating treatment. Start with defined population (particular disease) and randomly allocate to exposed or not exposed (treatment/placebo) and follow in time to observe outcome (cure/improvemnt - no change).
Advantages: protection against confounders, directly estimate risk, multiple outcomes.
Disadvantages: costly, time consuming.
Rank the types of studies from least level of evidence to greatest
Case Series Ecological Cross-Sectional Case-Control Cohort RCT
