# Biostats 1

 What is prevelance and how is it calculated? P = (number of exisiting cases of disease at a given point in time)/(total population) P = incidence x duration What is incidence? Number of new cases that occur during a period of time. What is cumulative incidence? Proportion of people whop became diseased during a perior of time (probability/risk of disease during the period of time). What is sensitivity and how do you calculate it? Proportion of those with disease who tested positiveSensitivity = TP/(TP + FN) What is specificity and how do you calculate it? Proption of people without disease who test negativeSpecificity = TN/ (TN + FP) What is the PPV and how do you calculate it? Proportion of people who test positive that are really diseasedPPV = TP / (FP / TP) What is the NPV and how do you calculate it? Proportion who test negative and really aren't diseasedNPV = TN / (TN + FN) What factors change the PPV & NPV? changing disease incidence /prevalence What's a type 1 (alpha) error? What is it's measurement? Stating that there is an effect or difference when none exists; p is probablility of making type 1 error What's a type 2 (beta) error? Stating that there is not an effect or difference when one exists; What is the power of a study? Probablilty of getting the right answer to the study. What factors change the power of a study? Number of points in the populationDiffernece in complaince between groupsSize of expected effect What's a confidence interval? Range of values in which a specified probability of the means are expected to fall. When is a confidence interval useless? Interval includes 0 or 1 = H0 is trueIntervals overlap = not significantly different What is an experimental study with random allocation? Randomised controlled trial What's an experimental study without random allocation? Non-randomized controlled trial what's an ovservational study with no comparison group? Descriptive study What's an ovservational study with a comparison group? Analytical Study (cohort, case control, cross sectional) What's a cohort study? Analytical StudyTaking an exposure group and looking forward for an outcome What's a Case-control study? Analytica study looking from an outcome back to evaluate for exposure what's a cross-sectional study? Looking at the exposure and outcome status at the same moment in time What's the correlation coeficient and what does it mean? (r) bewtween -1 and +1The closer to +1 the stronger the correlation between the two variables What is the coefficent of determination? r2this is the value that's reported What is a case report and what are it's purposes? Describe experience of individula/populationFirst step in identification of new things1. describe and evaluate trends in outcomes 2. provide data for panning3. suggest new research What's a correlation/ecological study and what are strengths/limitations? Study of group characteristics; measure of association; non-comparative to another groupStrengths: quick, cheap, easyWeaknesses: inability to link exposure and disease; lack of control over confounding factors What is ecologic fallacy? Inapporpriate inference from ecological data (relationship of groups doesn't mean relationship of individuals) What are the pro/cons of cross sectional study? Strengths: quick, cheap, establish "burden of diease"Weaknesses: confuses causation and correlation What are the pro/con of case control studies? Strengths: evaluation of rare diseases with long latency, quick and cheap, multiple factors for a single diseaseWeakness: limited for rare exposures, no incidence rates, difficult to establish temporal relationship, prone to bias What are the strengths of a cohort study? Rare exposures, good information collectedLeast bias, clear temporal relationshipdirect measurement of incidnce in exposed vs non-exposed What are limitations of cohort studies? Ineficient for rare diseasesExpensive and time consumingRetrospectives are more vulnerable to bias What is an experimental study? What are key components of the study? controlled expeirmentRandomization, blinidng, placebo controlledCross over - each subject serves as their own controlFactorial design - allows for evaluation of multiple hypothesises What's primary disease prevention? Remove the risk (ie vaccination) What's secondary disease prevention? Early detection and treatment (ie, pap smear) What's tertiary disease prevention? reduce complications of the disease (ie; insulin for diabetes) How do you fill in the box for all the calculations? What's an odds ratio and how is it calculated? odds of being diseased if exposed: odds of being diseased if unexposed(A/B) / (C/D) = OR Whats an absolute (attributable) risk and how's it calculated? % increase of disease attrributabe to exposure What's an absolut (attribuateble) risk reduction and how's it calculated? % differnce in diseased between normal and treated groups What's the relative risk and how's it calculated? The probability of getting diseased in exposeure group when compared to normal What's the Relative risk reduction and how's it calculated? % attributable of diseased to a factor (ie: 1/3 of pneumonia is caused by smoking) How do you calculate Confidence Interval Confidence Interval = (mean ±Z( σ /√N))Z = 2; σ = SD Authoreschott ID79000 Card SetBiostats 1 DescriptionEpidemiology and Biostatistics Updated2011-04-12T14:18:37Z Show Answers