EBDM Study Designs 101 Flashcards
Biostatistics
The use of numerical techniques to extract information from data. The discipline focuses on the variation in sets of data, that occurs either because of some intervention or from the effect of other variables linked to the data. Biostatistical tests frequently look at the comparison between an observed effect, or a difference, and the anticipated results of random variation. Some have stated that biostatistics is the study of variability or uncertainty.
Population
The group of people who meet the criteria for entry into a study (whether they actually participated in the study or not). The group of people to whom the study results can be generalized.
Sample
That part of the population selected to be studied. The group specifically included in the actual study.
Outcome (dependent variable)
The target variable of interest. The variable that is hypothesized to depend on or be caused by another variable, the independent variable
Clinical Epidemiology
- A discipline that describes quantifies and postulates causal mechanisms for health phenomena in populations.
- frequently used to investigate possible causality through non-experimental data
Causality
The relationship between cause and effect. A fundamental concept in epidemiology. A given cause may be necessary, sufficient, neither or both. A “necessary” cause must always precede an effect. A “sufficient” cause inevitably initiates an effect but is not the only necessary cause for a given effect.
Case Series
A study design that reports data on a series of consecutive patients with the same diagnosis. It is crucial that a rigorous case definition be used to insure all actually are members of the same group. There is NO control group.
Prospective Observational Study
Any study done forwards in time. Important in studies on therapy, prognosis, or harm, where retrospective studies make hidden biases more likely. When used to study potential causes of a disorder, it is a prospective investigation in which a cohort of individuals who do not have evidence of an outcome of interest but who are exposed to the putative cause are compared with a concurrent cohort who are also free of the outcome but not exposed to the putative cause. Both cohorts are then followed forward in time to compare the incidence of the outcome of interest. When used to study the effectiveness of an intervention, it is a prospective investigation in which a cohort of individuals who receive the intervention are compared with a concurrent cohort who do not receive the intervention. Both cohorts are then followed forward in time to compare the incidence of the outcome of interest.
Retrospective Observational Study
Any study in which the outcomes have already occurred before the study and collection of data has begun.
Randomized Clinical Trial
An interventional study in which the patients are randomly selected or assigned either to a group which gets the intervention or to a control group. Essentially an experiment in which individuals are randomly allocated to receive or not receive an experimental preventive, therapeutic, or diagnostic procedure and then followed to determine the effect of the intervention
Systematic Review
A formal review of a focused clinical question based on a comprehensive search strategy and structured critical appraisal of all relevant studies.
Incidence
- The rate at which an event occurs in a defined population over time. The number of new cases (or other events of interest) divided by the total population at risk.
- number of new cases of disease occurring during a specified period of time; expressed as a percentage of the number of people at risk
- this data should only come from prospective Cohort studies or RCTs
Prevalence
- The proportion of people affected with a particular disease at a specific point in time
- an accurate prevalence rate can inform a clinician’s pre-test probability estimate
Probability
Chance or frequency of a random event occurring (Frequentist). Also, the quantitative estimate of the likelihood of a condition existing (as in diagnosis) or of subsequent events (such as in an intervention study) given some assumed situation or patient scenario (Conditional/Bayesean).
Odds Ratio
A ratio of the odds of an event in an exposed group to the odds of the same event in a group that is not exposed. An odds ratio of 1 indicates that the condition or event under study is equally likely in both groups. An odds ratio greater than 1 indicates that the condition or event is more likely in the first group. And an odds ratio less than 1 indicates that the condition or event is less likely in the first group. For example, suppose that in a sample of 100 men, 90 have drunk beer in the previous week, while in a sample of 100 women only 20 have drunk beer in the same period. The odds of a man drinking beer are 90 to 10, or 9:1, while the odds of a woman drinking beer are only 20 to 80, or 1:4 = 0.25:1. Now, 9/0.25 = 36, so the odds ratio is 36, showing that men are much more likely to drink beer than women.
What is important to remember about Disease Causality?
statistical association between a risk factor and disease does NOT equate to causality
Strength of association
magnitude of the measure of association
consistency upon repitition
different studies find consistent results
specificity
specific risk factor associated with specific diseases
time sequence
shorter the duration of time the stronger the evidence
dose response
increase in the risk factor dose is associated with an increase in rate of outcome