Epidemiology Flashcards
Incidence risk
Definition: Probability of new cases occurring in a defined population over a specific period.
Formula: IncidenceRisk = NewCases/
PopulationatRisk
Example: If 50 out of 1,000 people develop flu in a year, the incidence risk is 50/ 1000 = 0.05 or 5%
Case control study
Definition: Observational study that compares individuals with a disease (cases) to those without (controls) to identify risk factors.
Example: Investigating smoking history in lung cancer patients (cases) and comparing it to non-patients (controls).
Cohort study
Definition: Observational study that follows a group exposed to a risk factor and a group not exposed to compare incidence of disease.
Example: Following smokers and non-smokers over time to study the incidence of lung cancer in each group.
Incidence rate
Definition: Rate at which new cases occur in a population per unit of time.
Formula: Incidence Rate = New Cases / Person-Time at Risk
Example: In a study with 100 person-years of observation, 20 new cases of a disease yield an incidence rate of 20 / 100 = 0.2 cases per person-year.
Prevalence
Definition: Proportion of a population with a disease at a given point in time.
Formula: Prevalence = Existing Cases / Total Population
Example: If 100 out of 1,000 people in a community have diabetes, the prevalence is 100 / 1000 = 0.1 or 10%.
Incidence
Definition: Refers to the number of new cases of a disease in a population during a specific period.
Formula: Incidence = Count of New Cases Over Time
Example: If a city has 200 new flu cases in January, the incidence is 200 for that month.
Sensitivity
Definition: Proportion of true positives correctly identified by a test.
Formula: Sensitivity = True Positives / (True Positives + False Negatives)
Example: If a COVID test correctly identifies 90 out of 100 infected individuals, sensitivity is 90 / 100 = 0.9 or 90%.
Specificity
Definition: Proportion of true negatives correctly identified by a test.
Formula: Specificity = True Negatives / (True Negatives + False Positives)
Example: If a COVID test correctly identifies 95 out of 100 healthy individuals, specificity is 95 / 100 = 0.95 or 95%.
Negative predictive value
Definition: Probability that individuals with a negative test truly do not have the disease.
Formula: NPV = True Negatives / (True Negatives + False Negatives)
Example: If 150 out of 160 people with a negative COVID test are truly disease-free, NPV is 150 / 160 = 0.9375 or 93.75%.
- Positive Predictive Value (PPV)
Definition: Probability that individuals with a positive test truly have the disease.
Formula: PPV = True Positives / (True Positives + False Positives)
Example: If 80 out of 100 people with a positive COVID test actually have COVID, PPV is 80 / 100 = 0.8 or 80%.
Odds ratio
Definition: The odds that an event occurs in one group compared to the odds of it occurring in another group, often used in case-control studies.
Formula: Odds Ratio = (A / B) / (C / D) = (A × D) / (B × C)
Risk ratio
Definition: The risk of an event occurring in the exposed group compared to the risk in the unexposed group, commonly used in cohort studies.
Formula: Risk Ratio = (A / (A + B)) / (C / (C + D))
Categorical data - which test
Chi squared
Continuous - normally distributed - which test
Mean and standard deviation
T test
Continuous - skewed - which test
Median and interquartile range
Mann Whitney U test
