Randomized Controlled Trial is a prospective, analytical, experimental study using primary data generated in the clinical environment. Individuals similar at the beginning are randomly allocated to two or more groups (treatment and control) then followed to determine the outcome of the intervention.
Cohort Study (prospective) is a study of a group of individuals, some of whom are exposed to a variable of interest (e.g., drug or environmental exposure), in which participants are followed up over time to determine who develops the outcome of interest and whether the outcome is associated with the exposure.
Cohort Study (retrospective) is when data is gathered for a cohort that was formed sometime in the past. Exposures and outcomes have already occurred at the start of the study. You are studying the risk factor and see if you can associate a disease to it. Individuals split by exposure.
Case Control Study is a study in which patients who already have a specific condition or outcome are compared with people who do not. Researchers look back in time (retrospective) to identify possible exposures. They often rely on medical records and patient recall for data collection. Individuals split by disease.
Survey Study is an epidemiologic study that produces survey results, and will consist of simultaneous assessments of the health outcome, primary risk exposure and potential confounders and effect modifiers. Two types of survey research are cross-sectional and longitudinal studies.
Cross-Sectional Study is the observation of a defined population at a single point in time or during a specific time interval to examine associations between the outcomes and exposure to interventions. Exposure and outcome are determined simultaneously. Often rely on data originally collected for other purposes.
Longitudinal Study follow subjects over time with continuous or repeated monitoring of risk factors or health outcomes, or both. Researchers conduct several observations of the same subjects over a period of time, sometimes lasting many years.
Before and After Study is a study in in which observations are made before (pre) and after (post) the implementation of an intervention, both in a group that receives the intervention and in a control group that does not.
Case Series and Case Reports are descriptive study/studies that consist of collections of reports on the treatment of individual patients or a report on a single patient.
Systematic Review usually focuses on a specific clinical question and conducts an extensive literature search to identify studies with sound methodology. The studies are reviewed, assessed, and the results summarized according to pre-determined criteria of the review question.
Meta-Analysis takes a systematic review one step further by combining all the results using accepted statistical methodology.
Descriptive statistics are used to DESCRIBE the study population using calculations, tables and/or graphs.
Statistics of central tendency:
| Mean | The sum of all values in a group/# items in the group (Average) |
| Median | The value in the middle of a group of values (Typical) |
| Mode | The value that appears the most in a group of values (Most Common) |
Statistics of variation:
| Range |
Range = (Highest # – Lowest #) The simplest way to describe variation in a set of values Very sensitive to data that doesn’t fit the typical pattern (called outliers) |
| Interquartile Range (IQR) |
Identifies variation in a set of values after removing outliers (focus on the 50% of data closest to the mean) Reported as a range of numbers |
| Standard Deviation (SD) |
Identifies variation in a set of values by estimating the average distance of each score from the mean Small SD = more concentrated Large SD = less concentrated |