Biostats Flashcards
If a sample has a normal distribution, what percent of the sample is included in…
- 1 SD
- 2 SD
- 3 SD
- 1 SD = 68%
- 2 SD = 95%
- 3 SD = 99.7%
How do the mean, median, and mode relate if a data set is positively skewed? Negatively skewed?
- positive: mean > median > mode (long tail to right)
- negative: mode > median > mean (long tail to left)
What are type I and type II errors?
- type I is rejecting the null when it is actually true
- type II is accepting the null when it is actually false
What are alpha and beta values? How do they relate to error?
- alpha is the probability of a type I error and is equal to the p value
- beta is the probability of a type II error and 1 - B equals the power of the study
What is the power of a study?
- it equals 1 - B
- it increases with sample size as the probability of a type II error decreases
What are the following tests used for?
- unpaired t-test
- paired t-test
- ANOVA
- Chi squared
- unpaired T-test: compares numerical measurements taken from two different groups
- paired T-test: compares two different numerical measurements taken from a single group
- ANOVA: compares numerical means of three or more groups
- Chi squared: compares categorical outcomes between two or more groups
What is the best statistics test to compare the BMI in patients before versus after getting a sleeve gastrectomy?
paired T-test
What is a Kaplan-Meier analysis good for?
identifying differences in survivorship over time between two or more groups
What are multivariate logistic and multivariate linear regressions used for?
- multivariate logistic regression: to identify and adjust for multiple potential factors contributing to a categorical outcome
- multivariate linear regression: to identify and adjust for multiple potential factors contributing to a numerical outcome
What are case reports and case series?
- a case report is one of a single event or patient
- a case series is of a small number of similar events or patients
What is the difference between the following:
- cross-sectional study
- cohort study
- case-control study
- cross-sectional study: analyze a population at a particular moment in time to determine the prevalence of factors and disease
- cohort: a population of subjects are analyzed to associate certain factors with an outcome (prospective or retrospective), determining the relative risk
- case-control: patients who had an outcome happen are compared to those who did not (always retrospective and can only determine an odds ratio)
What is a propensity-score-matched study?
- an observational study that attempts to reduce the presence of confounding variables and replicate a RCT
- cases are selected so that the subjects in both groups are similar across multiple factors
What is a crossover study?
one in which each subject receives both interventions, serving as their own control
What occurs in the four phases of a clinical trial?
- 1: a small number of healthy subjects are used to test the pharmacology and side-effects of the drug
- 2: a small number of diseased subjects are used to test the efficacy and dosing of the drug
- 3: RCT to compare the drug to an existing therapy
- 4: ongoing surveillance after the drug is approved to identify long-term side-effects and efficacy
What are absolute and relative risk?
- absolute is the overall probability of the outcome (percent it occurred in both groups)
- relative is the probability of the outcome occurring in the exposed group divided by the probability of it occurring in the unexposed group
