Biostats Flashcards
The probability that disease is present given a positive result
Positive predictive value
The probability that disease is absent given a negative result
Negative predictive value
A ratio representing the likelihood of having the disease given a positive result
Positive likelihood ratio
LR+ = Sensitivity ÷ (1 − Specificity)
A ratio representing the likelihood of having the disease given a negative result
Negative likelihood ratio
LR− = (1 − Sensitivity)
÷ Specificity
Correlation coefficient (r) values range from -1 to 1
The closer the r value is to its margins [-1, 1], the ______ the association.
stronger
- ie: if the correlation coefficient (r = -0.39) and is statistically significant (p = 0.005), the association is weak because its value is closer to 0 than to 1.
_______ is a measure of effect used in survival analysis (or time-to-event analysis).
What is the null value?
Hazard Ratio
The null value for HRs is 1.00:
HR = 1.00 means that there is no difference in risk between the 2 groups.
HR <1.00 indicates a protective effect, whereas HR >1.00 indicates a detrimental effect.
_________ of a medication is a measure of its possible BENEFIT minus its possible HARM.
net clinical benefit
For example, in patients with refractory or untreatable cancer, chemotherapy treatment leading to significant clinical improvement might result in a favorable NCB despite substantial toxicity of the medication.
The basic premise of the ________ principle is that participants in trials should be analyzed in the groups to which they were randomized, regardless of whether they received or adhered to the allocated intervention and regardless of whether they withdrew from treatment.
intention-to-treat
holds that randomization is of paramount importance and that deviation from the original randomized groups can contaminate the treatment comparison.
_____ quantifies the proportion of risk reduction attributable to a specific intervention or exposure as compared to a control
Relative risk reduction
RRR = (risk in unexposed − risk in exposed) / (risk in unexposed)
The ____ usually indicates how high or low the risk for disease is among the exposed compared to the unexposed group.
Relative risk
RR = Risk of disease in exposed group / risk of disease in unexposed group
The________ is a quantitative measure of inter-rater reliability (sometimes referred to as inter-rater concordance). It reflects the extent to which inter-rater agreement represents an improvement on chance agreement alone.
kappa statistic
Kappa values range from -1 (perfect disagreement) to +1 (perfect agreement), with kappa = 0 suggesting agreement due to chance
The probability of a diseased person testing positive
- (probability of detecting the disease if it is present)
Sensitivity
The probability of a nondiseased person testing negative
Specificity
A ____ test can test the difference between 2 paired means; patients serve as their own control (eg, mean blood pressure before and after treatment in the same subjects).
paired t-test
_____ test is best suited for a scenario where the mean values of a continuous variable in several groups (categorical variable) are being compared.
ANalysis Of VAriance (ANOVA)
A funnel plot is helpful in assessing ______
publication bias
- 95% of studies should lie within the triangle centered on the summary estimate and extending 1.96 standard errors on either side
________ occurs when the magnitude or direction of the effect of the independent variable on the dependent variable (outcome) varies depending on the level of a third variable.
- Separate (stratified) analyses should be conducted for each level of the effect modifier.
Effect modification
attributable risk aka ______
risk difference
- measure of excess incidence of disease d/t a particular factor (ie: smoking)
If the CI does not include the ______, that implies that the result was statistically significant
null value (ie: 0)
Positive and negative predictive values are used to describe the clinical usefulness of a respective positive or negative test result.
However, they are not intrinsic characteristics of a test and can vary based on _______
disease prevalence in the tested population.
True/False
Nonoverlapping confidence intervals ALWAYS imply a statistically significant difference between groups. However, the opposite is not necessarily true.
true
There is an increased risk for type __ errors when multiple simultaneous hypotheses are tested at set p-values.
Interpretation of findings in clinical trials when multiple outcome measures are used without adjustment of the significance level may result in spurious findings and invalid conclusions.
Type I errors (ie, false positives)
When hazard ratios or Odd ratios are included, statistically significant confidence intervals means __________
CI do not include the null value of 1.00 for HRs or 1/0 for OR
________ refers to repeating primary analysis calculations after modifying certain criteria or variable ranges; the goal is to determine whether such modifications significantly affect the results initially obtained.
(ie: exclude high fluctuations in glucose lvls)
Sensitivity analysis
