Biostats Flashcards
How many data points are within 1, 2, and 3 standard deviations?
- 1SD = 68%
- 2SD = 95%
- 3SD = 99.7%
What makes a set of data positively skewed?
mean > median > mode (long tail to the right)
What makes a set of data negatively skewed?
mode > median > mean (long tail to the left)
What is a type I error?
- the null is rejected when it is actually true
- a false positive
- probability of this equals “a”
What is a type II error?
- the null is accepted when it is actually false
- a false negative
- equals beta
What increases the power of a study?
the sample size
How is the power of a study calculated?
power = 1 - B
What do the alpha and beta values represent?
- alpha is the risk of a type I error (rejecting the null when it is true, false positive)
- beta is the risk of a type II error (accepting the null when it is false, false negative)
What tests are used to compare categorical outcomes between two or more groups?
- chi squared
- or Fischer’s exact
What is the difference between a multivariate logistic regression versus a multivariate linear regression?
- logistic is for categorical outcomes
- linear is for numerical outcomes
What is the difference between a cohort study and a case-control study?
- cohort: population of subjects are analyzed to associate certain factors with an outcome, can be retrospective or prospective, gives a relative risk
- case-control: patients who had an outcome happen are compared to those that didn’t, always retrospective, gives an odds ratio
What is a cohort study?
- looks at a group of subjects to look for factors associated with an outcome
- can be retrospective or prospective
- gives a relative risk
What is a case-control study?
- looks at a group of subjects with a particular outcome and compare them to those who didn’t
- can be only be retrospective
- gives an odds ratio
What is a propensity-score-matched study?
an observational study that attempts to replicate an RCT by selecting cases so that the subjects in both groups are similar across multiple factors
What happens in each of the following phases of a drug trial?
- phase 1
- phase 2
- phase 3
- phase 4
- phase 1: tests on a small group of healthy individuals for safety
- phase 2: tests on a small number of diseased subjects for dosing/efficacy
- phase 3: RCT to compare to existing therapies
- phase 4: ongoing long-term evaluation to look at side-effects and efficacy
