BIOSTATS Flashcards
What is a Cross-Sectional Study
A study that collects data from a group of people to assess the FREQUENCY OF DISEASE AT A PARTICULAR POINT IN TIME It measures DISEASE PREVALENCE and RELATED RISK FACTORS PREVALENCE; can show risk factor association with a disease but DOES NOT ESTABLISH CAUSALITY mneumonic: think of a cross section as a slice of something; and this study is a “slice of time” BASICALLY: study a population at any point of time i.e you don’t care what they had before nor do you go ahead and follow them. you just collect data regarding the present state of affairs. It provides info regarding disease prevalence. AKA “SNAPSHOT STUDY” or “PREVALENCE STUDY”
What is a Case-Control Study?
Compares a group of people WITH A DISEASE to a group WITHOUT A DISEASE. Measures ODDS RATIO (OR): ie: patients with COPD have a higher odds of history of smoking than those without COPD” mneumonic: ORs (operating rooms) have controlled cases and people with disease BASICALLY: 1. both exposure and outcome have occurred before the start of the study 2. the study proceeds backwards from the effect to the cause 3. it uses a control or comparison group to support or refute an inference.
What is a Cohort Study?
Compares a group with a given exposure or risk factor to a group without such exposure; looks to see if an exposure increases the likelhood of disease; a group of people within a population is followed over a specified period of time to track who experiences or develops the same significant life event or treatment Looks to see if exposure increases the likelihood of disease Measure with RELATIVE RISK; ie: smokers have a higher risk of developing COPD than nonsmokers Mnemonics: RELATIVES = a COHORT of similar people; same house = same exposures BASICALLY: 1. the cohorts are identified prior to the appearance of the disease under investigation. 2. the study groups are observed over a period off time to determine the frequency of disease among them 3. the study proceeds from cause to effect.
Twin concordance study
compares the frequency with which both monozygotic twins or both dizygotic twins develop the same disease Measures: heritability vs environmental factors
Adoption study
compares siblings raised by biological vs adoptive parents Measures heritability and influence of environmental factors
Triple-blind study
blinding of doctors, patients, AND the researchers analyzing the data
What are the different phases of a clinical trial?
Phase I: healthy volunteers, to check the drug safety Phase II: Sick people (diseased pts), to check the dosing efficiency Phase III: Randomized, check vs. standard Phase IV: Long term, check term fx
Sensitivity tests___?
Measure of positives; “positive people are more sensitive”
Value approaching 100% is desireable for RULING OUT disease and indicates a LOW FALSE-NEGATIVE RATE. When negative, rules OUT disease.
TP/(TP + FN) OR (1 - false neg rate)
Note: high sensitivity test used for screening diseases with low prevalence.
Drug Trial Phases
**Phase 1: **“Is it safe?” Healthy volunteers.
**Phase 2: **“Does it work?” Sick people. Dosing and efficacy.
**Phase 3: **“Is it as good or better?” Randomized. Checks vs a standard.
**Phase 4: **“Can it stay?” Long term. Checks long term effects.
Specificity tests _____?
Measures the true-negative rate. “Negative people tend to be more specific and nitpicky”
Value approaching 100% is desireable for RULING IN disease and indicates a LOW FALSE-POSITIVE RATE. When positive, rules IN disease.
TN/(TN + FP) or (1 - false positive rate)
NOTE: High specifictiy test used for confirmation after a positive screening test.
Positive Predictive Value
Proportion of positive test results that are true positive.
TP/(TP + FP)
PPV varies directly with prevalence or pretest probability: high pretest probability means HIGH PPV
Negative Predictive Value
Proportion of negative test results that are true negative.
TN/(FN + TN)
NPV varies inversely with prevalence or pretest probability: high pretest probability means LOW NPV
Incidence
All new cases.
Implementing prevention methods will decrease the new cases, thus decreasing incidence.
Prevalence
All the current cases.
Increasing treatment efficacy (or anything else to increase survival) will increase prevalence. Prevention methods will likely decrease the prevalence as well.
Odds Ratio
Used in **Case-Control **studies.
Odds that the group with the disease (cases) was exposed to a risk factor divided by the odds that the group without the disease (controls) was exposed.
OR = ad/bc
