Evidence based medicine Flashcards
What do case-control studies look at?
compare risk factor frequency
-useful to study individuals w/ a disease compared to individuals without the disease
-evaluates risk factors and outcomes for the disease
What do retrospective cohort studies look at?
compare disease incidences
-follows a population of patients with a disease over time
-likely to yield important information about the natural history of a disease
What do prospective cohort studies look at ?
compare disease incidences
Which tests can be used for a single sample metric test?
-t test
-Z test
Which tests can be used for multiple, independent samples in a metric test?
-two group t-test
-Z test
Which test can be used for paired samples in a metric test?
paired t-test
What test can be used for single sample nonmetric tests?
-chi-square
-K-S
-runs
-binomial
Which tests can be used for multiple, independent samples in a nonmetric test?
-chi-square
-Mann-Whitney
-median
-K-S
Which tests can be used for paired samples in a nonmetric test?
-sign
-Wilcoxon
-McNemar
-chi-square
What are examples of metric (parametric) tests?
-interval = interval between observations in terms of fixed until of measurement (temperature)
-ratio = scale has a fundamental zero point (age, income)
What are examples of nonmetric (nonparametric) tests?
-nominal = define an attribute (gender, marital status)
-ordinal = rank or orders the observation as scores or categories from low to high in terms of “more or less” (education, attitude, opinions)
What is a type 1 error?
-alpha error
-incorrectly rejects null hypothesis
-says there’s a difference when there really isn’t
-alpha is the probability of making a type 1 error
What is a type 2 error?
-beta error
-incorrectly accepting the null hypothesis
-says there’s no difference when there is
-beta is the likelihood of making a type 2 error
-results in there are too few subjects
What is p-value?
risk of a false positive result due to chance (describes the strength of the result)
-if < 0.01 highly statistically significant
-if </= 0.05 statistically significant
-if > 0.05 statistically insignificant
What is statistical power?
likelihood a study correctly disproves the null hypothesis
-likelihood of finding a difference between two groups
How do you calculate power?
power = 1-beta
What does the power of a study depend on?
-effect size
-level of significance desired (p value)
-sample size
What is a confidence interval?
range w/in which magnitude of effect lies
What is the confidence interval if alpha = 0.05?
95%
When is a confidence interval statistically significant?
-CI does not include or span the “no effect point” of one or zero for risk ratios like relative risk and odds ratio
-numbers do no overlap
Define sensitivity.
proportion of patients with a disease who test positive
Define specificity.
proportion of patients without a disease who test negative
How do you calculate PPV?
PPV = A/A+B (true positive/total number of positives)
How do you calculate NPV?
NPV = D/D+C (true negative/total number of negatives)
One the 2x2 grid what category is on top (x-axis) and which is on the side (y-axis)?
-x = disease
-y = test
How do you calculate sensitivity?
A/A+C
How do you calculate specificity?
D/B+D
How do you calculate relative risk reduction?
RRR = (1-RR)/RR
How do you calculate number needed to treat?
100/absolute risk reduction
