Critical numbers Flashcards
Define prevalence.
Number of existing cases in a defined population at a defined point in time, divided by the number of people in the population at that time.
Define risk
The number of new cases in a defined population at risk during a specified time people.
The defined population at risk does NOT include existing cases
What is the secondary attack rate?
Number of exposed people developing the disease within the range of the incubation period ÷ total number of people who are exposed/susceptible x 100
Define odds.
Number of new cases in a specified time period ÷ number who did not become a case during that time period
Define incidence rate.
Number of new cases in a specified time period ÷ total person-time at risk during that time period.
From what study type can you not calculate a risk ratio?
Case control studies
What is a p value?
A calculated probability of finding the observed or more extreme results when the null hypothesis of a study question is true. Provides an estimate of the probability that the results are due to chance.
What p value suggests statistical significance?
0.05
What is a null hypothesis?
A statement that proposes that no statistical significance exists in a set of given observations.
The null hypothesis is set up in opposition to an alternative hypothesis and attempts to show that no variation exists between variables, or that a single variable is no different than its mean.
What is the alternative hypothesis?
Opposite of the null hypothesis. Usually the hypothesis that you are trying to prove.
Name four types of linear regression
- Linear regression
- Logistic regression
- Poisson regression
- Cox regression
What do the four types of of regression estimate or model?
Linear regression = estimated mean differences between groups
Logistic regression = binary outcomes, models an odds ratio
Poisson regression = models rate ratios
Cox regression = models hazard ratios
What is regression analysis?
A powerful statistical method that allows you to examine the relationship between two or more variables of interest. Helps to understand how the typical value of the dependent variable changes when one of the independent variables is varied and the others remain fixed.
What would a relative risk of 1 suggest?
Incidence in the exposed group is the same as incidence in the non-exposed group.
No increased risk = no association
What would a relative risk of <1 suggest?
That incidence in the unexposed group is greater than incidence in the exposed group.
Decreased risk = negative association
What would a relative risk of >1 suggest?
Incidence in the exposed group is greater than incidence in the non-exposed group.
Increased risk = positive association
Define bias.
A systematic error in studies that lead to an error in conclusions or skewed results.
How do you eliminate/reduce bias?
Blinding
What is blinding?
When patients/subjects do not know which treatment they are receiving in order to ensure that the results are not affected by the placebo effect (power of suggestion).
What is double blinding?
Both the researchers and the subjects/patients do not know which treatment they are receiving.
What is simple random sampling?
A process in which each member of the population has an equal probability of being selected.
What is systematic sampling?
Members of the population are selected at equal intervals
What is stratified sampling?
The population is partitioned into strata (groups) and a sample is randomly selected within each strata.
What is cluster sampling?
The population are partitioned into clusters (groups) and a sample of clusters is selected. All people in the selected clusters are included in the sample.