- What type of study is a case control study?Observational and retrospective
- What type of study is a Cohort study?Observational and prospective or retrospective
- what type of study is a Cross-sectional study?Observational
- what is the design of a case-control study?Compares a group of people with disease to a group without disease Looks for prior exposure or risk factor Asks what happened
- what a measure/example of Case-control study?Odds Ratio (OR) patients with COPD had higher odds of hx smoking
- what is the design of a cohort study?Compares a group with a given exposure or risk factor to a group without such exposure. - looks to see if exposure increases likelihood of disease - can be prospective (who will get X) or retrospective (who developed X)
- what is a measure/example of a cohort study?Relative risk (RR) smokers have higher risk of developing COPD than non smokers
- what is the design of a cross-sectional study?collects data from a group of people to assess frequency of disease and related risk factors at a particular point in time - asks what is happening
- what is a measure/example of a cross sectional study?disease prevalence Can show risk factor association with disease but does not establish causality
- what is the design of a twin concordance study?compares the frequency with which both monozygotic twins or both dizygotic twins develop same disease
- what does twin concordance study measure?Heritability
- what is the design of an adoption study?compares siblings raised by biological vs adoptive parents
- what does an adoption study measure?measures heritability and influence of environmental factors
- what is a clinical trialExperimental study involving humans - compares therapeutic benefits of >= two Tx or 1 Tx and placebo.
- what improves the quality of a clinical trial?"when study is randomized, controlled, and double blinded"
- what is the study sample in a phase I clinical trial?small number of healthy volunteers
- what is the purpose of a phase I clinical trial?"asses safety, toxicity, and pharmacokinetics"
- what is the study sample in a phase II clinical trial?small number of patients with disease of interest
- what is the purpose of a phase II clinical trial?"assesses treatment efficacy, optimal dosing, and adverse effects"
- what is the study sample in a phase III clinical trial?large number of patients randomly assigned either to the treatment under investigation or to the best available treatment or placebo
- what is the purpose of a phase III clinical trial?compares new treatment to the current standard of care
- what is the study sample in a phase IV clinical trial?postmarketing surveillance trial of patients after approval
- what is the purpose of a phase IV clinical trial?detects rare or long term side effects
- what properties of a diagnostic test are fixed?sensitivity and specificity
- what properties of a test vary with prevalence or pretest probability?PPV NPV
- what is the sensitivity of a test?"(true positive rate) portion of all people with disease who test positive, or the probability that a test detects disease when disease is present"
- what is the formula for sensitivity (true positive rate) of a dx test?=TP/ (TP+FN) = 1- false negative rate
- important things to remember about test sensitivity?PID= Positive in Disease SNOUT= Sensitivity rules out
- what is a highly sensitive test good for?value approaching 100% is desirable for ruling out disease and indicates a low false negative rate. - used for screening in diseases with low prevalence
- what is true of a test with 100% sensitivity?TP/(TP+FN)=1 FN=0 all negatives must be TN
- what is the specificity of a dx test?"(true negative rate) proportion of all people without disease who test negative, or the probability that a test indicates non disease when disease is absent"
- what is the formula for specificity of a dx test?=TN/(TN+FP) =1- False positive rate
- what is important to remember about the specificity of a dx test?NIH= Negative in Health SPIN= Specificity rules in
- what is true of a test that has specificity of 100%?TN/(TN+FP)=1 FP=0 all positives must be TP
- what is a highly specific test good for?value approaching 100% is desirable for ruling in disease and indicates a low false positive rate. used as a confirmatory test after a positive screening test
- what are the features of ELISA screening in HIV?sensitive high FP low threshold
- what are the features of confirmatory western blot for HIV?specific high FN high threshold
- what is PPV?proportion of positive test results that are true positive probability that pt actually has dx after positive test result
- what is the formula for PPV?=TP/(TP+FP)
- PPV varies with what?directly with prevalence or pretest probability
- what is the implication for PPV of a high pretest probability?high PPV
- what is NPV?proportion of negative test results that are true negative probability that pt actually is disease free if given a negative test result
- what is the formula for NPV?=TN/(FN+TN)
- NPV varies with what?varies inversely with prevalence or pretest probability
- what are the implications of high pretest probability for NPV?high pretest probability --> low NPV
- what is the incidence rate?# new cases in a specified time period / population at risk during same time period
- important to remember about incidence?Incidence looks at new incidents
- what is prevalence?# of existing cases / population at risk = incidence rate X average disease duration
- important to remember about prevalence?prevalence looks at all current cases
- when is prevalence > incidence?for chronic diseases
- when is Odds ratio used?typically in case control studies
- what is OR?odds that the group with the disease (cases) was exposed to a risk factor (a/c) divided by the odds that the group without the disease was exposed (b/d) =ad/bc
- when is Relative risk used?typically in cohort studies
- what is RR?risk of developing disease in exposed group divided by risk in unexposed group = (a/(a+b))/(c/(c+d))
- if prevalence is low then RR= ?OR
- what is attributable risk?"the difference in risk between exposed and unexposed groups, or the proportion of disease occurrences that are attributable to the exposure = (a/(a+b))-(c/(c+d))"
- what is absolute risk reduction?absolute reduction in risk associated with a treatment as compared to a control
- what is the number needed to treat?number of patients who need to be treated for 1 patient to benefit = 1/AAR
- what is the number needed to harm?number of patients who need to be exposed to a risk factor for 1 patient to be harmed = 1/attributable risk
- what is precision?the consistency and reproducibility of a test the absence of random variation in a test
- what reduces precision in a test?random error
- what is the relationship between precision and standard deviation?increased precision --> lower standard deviation
- what is accuracy?the trueness of test measurements. the absence of systematic error or bias in a test
- what reduces accuracy in a test?systematic error
- when does bias occur?when there is systematic error or favor in a particular direction
- what is selection bias?"nonrandom assignment to participation in a study group (eg Berkson's bias, loss to follow up)"
- what is recall bias?knowledge of presence of disorder alters recall by subjects; common in retrospective studies
- what is sampling bias?subjects are not representative of the general population; therefore the results are not generalizable.= type of selection bias
- what is late-look bias?information gathered at an inappropriate time- e.g. using a survey to study a fatal disease
- what is procedure bias?"subjects in different groups are not treated the same- eg more attention is paid to treatment group, stimulating greater adherence"
- what is confounding bias?"occurs when factor is related to both exposure and outcome, but is not on the causal pathway; factor confuses effect of exposure on outcome"
- what is lead time bias?"early detection confused with increased survival; seen with improved screening (natural history of disease is unchanged, but early detection makes it seem as though survival is higher)"
- what is observer expectancy effect?occurs when a researcher's belief in the efficacy of a treatment changes the outcome of that treatment
- what is the Hawthorne effect?Occurs when the group being studied changes its behavior owing to the knowledge of being studied
- what are the ways to reduce bias?blind studies to limit influence of participants and researchers on interpretation of outcomes - placebo control groups - crossover studies (each subject acts as own control) to limit confounding bias - randomization (refer to your book for more info)
- what are the measures of central tendency?mean median mode
- what are the measures of dispersion?Standard Deviation (SD) Standard error of the mean (SEM) Z score Confidence interval
- what is a normal distribution?"Gaussian, also called bell shaped mean=median=mode"
- what is SEM?s/sqrt(n)
- what happens to SEM as sample size increases?SEM decreases
- what are the features of distribution with positive skew?"Typically, mean > median > mode. Asymmetry with longer tail on right. Mode is least affected by outliers in the sample"
- what are the features of distribution with negative skew?typically mean < median < mode asymmetry with longer tail on left
- what is null hypothesis?hypothesis of no difference
- what is alternative hypothesis?hypothesis of some difference
- what is type I error (a)?stating that there is an effect or difference when none exists (to mistakenly accept the alternative hypothesis and reject the null hypothesis)
- what is a?the probability of making a type I error.
- what is p judged against?a preset a level of significance ( usually <0.05)
- type I error is also known as what?false-positive error a=you sAw something that did not exist
- what is type II error (Beta)?Stating that there is not an effect or difference when one exists (to fail to reject the null hypothesis when it is in fact false)
- what is Beta?the probability of making a type II error
- a type II error is AKA?false-negative error Beta=you were Blind to a difference that did exist
- what is Power (1-Beta)?"probability of rejecting null hypothesis when it is in fact false, or the likelihood of finding a difference if one in fact exists"
- Power increases with what?"increased sample size increased expected effect size increased precision of measurement ""there is power in numbers"""
- what happens in meta-analysis?pools data and integrates results from several similar studies to reach an overall conclusion. high statistical power
- meta-analyses are limited by what?quality of individual studies or bias in study selection
- what is Confidence Interval?Range of values in which a specified probability of the means of repeated samples would be expected to fall
- what is the formula for CI?CI= range from [mean-Z(SEM)] to [mean + Z(SEM)]
- CI of 95% corresponds to what?p=0.05
- "for the 95% CI, Z=?"1.96
- "for the 99% CI, Z=?"2.58
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