Stats Flashcards
When would you use unpaired t test vs paired t test
unpaired if independent, paired if dependent
for correlation, what would you use for parametric (normally distributed) vs non parametric
parametric (normally distributed): Pearson’s coefficient
non-parametric: Spearman’s coefficient
Q: What is selection bias?
An error in assigning individuals to groups, leading to differences that may influence the outcome.
Sampling bias
Subjects are not representative of the population (e.g., volunteer bias).
Non-responder bias
Non-responders may differ significantly (e.g., poorer diets in non-responders to dietary surveys).
Prevalence/incidence bias (Neyman bias)
Missed cases (e.g., early fatalities or silent cases) are omitted.
Admission bias (Berkson’s bias)
Systematic differences in hospital-based studies due to exposure and disease occurrence increasing admission likelihood.
Healthy worker effect
Healthier individuals are more likely to be employed, skewing results.
Q: What is recall bias, and when is it a problem?
Recall bias is a difference in the accuracy of memories retrieved by study participants.
A patient with a disorder may recall exposure more thoroughly than controls.
Common in case-control studies.
Q: What is publication bias, and why is it important?
Failure to publish valid studies, often due to negative or uninteresting results.
Significant in meta-analyses, where excluding negative results distorts findings.
Q: What is work-up bias (verification bias)?
Occurs when comparing new diagnostic tests with gold standard tests.
Gold standard tests may be avoided if the new test is positive, especially if invasive (e.g., tissue biopsy).
Can distort sensitivity and specificity, requiring adjustment if unavoidable
Q: What is expectation bias (Pygmalion effect)?
Observers subconsciously measure or report data to favor the expected outcome.
A problem in non-blinded trials.
Q: What is the Hawthorne effect?
Describes a group changing its behavior due to the knowledge that it is being studied.
Q: What is late-look bias?
Occurs when data is gathered at an inappropriate time.
Example: Studying a fatal disease years later, after some patients have died
Q: What is procedure bias?
Occurs when subjects in different groups receive different treatments.
Q: What is lead-time bias?
Happens when a new test diagnoses a disease earlier than an existing test.
It appears to improve survival time but does not change the disease outcome.
Q: What is the goal of a Phase 0 clinical trial?
Exploratory studies to assess how a drug behaves in the human body.
Focus on pharmacokinetics and pharmacodynamics.
Involves a very small number of participants.
Determines feasibility for further phases.
Q: What is the goal of a Phase I clinical trial?
Safety assessment.
Determines side effects before larger studies.
Conducted on healthy volunteers.
Q: What is the goal of a Phase II clinical trial?
Assess efficacy in patients affected by a specific disease.
Subdivisions:
Phase IIa: Assesses optimal dosing.
Phase IIb: Assesses efficacy.
Q: What is the goal of a Phase III clinical trial?
Assess effectiveness of a treatment.
Involves 100-1000s of participants.
Often conducted as randomized controlled trials.
Compares new treatments with established treatments.
Q: What is the goal of a Phase IV clinical trial?
Postmarketing surveillance.
Monitors long-term effectiveness and side effects.
Q: What does a 95% confidence interval mean?
It means the interval should contain the true effect of an intervention 95% of the time.
Q: How is the standard error of the mean (SEM) defined?
A measure of the spread expected for the mean of the observations.
Indicates how “accurate” the sample mean is compared to the true population mean.
Q: What is the formula for SEM?
SEM = SD / √n
SD = standard deviation.
n = sample size.
As the sample size increases, the SEM becomes smaller.
