Behavioral Science Flashcards
Cross sectional Study
Collects data from a group of people to asses frequence of disease at a particular time
- Measures prevalence
- does not establish causality
What is happening?
Case-control study
Compares a group of people with disease to a group without disease
- looks for prior exposure or risk factor
- Measures: Odds Ratio
Asks “What happened?”
Cohort study
Compares a group witha given exposure or risk factor to a group without such exposure
- Looks to see if exposure increases the liklihood of disease
- Can be prospective ( who will develop the disease?) or retrospective ( who developed the disease?)
- Measures: Relative risk
Twin concordance study
Compares the frequency with which both monozygotic twins or both dizygotic twins develop same disease
- measures heritability and influence of environmental factors
- nature vs. nurture
Adoption Study
Compares siblings raised by biological vs. adoptive parents
- measures heritability and influence of environmental factors
Clinical Trial
Experimental study involving humans
- Compares therapeutic benefit of 2 or more treatments or tx vs. placebo
- quality improves when study is randomized, controlled or double blinded
- Triple-blinded= researchers are blinded
Drug Trials
- Phase I: assess safety, toxicity, and pharmacokinetics
- Phase II: assess treatment efficacy, optimal dosing, adverse effects
- Phase III: compares new treatment to current standard of care
- Phase IV: Detects rare or long term adverse effects
Evaluation of diagnostic test
Uses 2x 2 tables comparing test results with actual presence of disease
- True positive
- False positive
- True negative
- False negative
Sensitivity
True-positive rate
- proprotion of all people with disease who test positive
- probability that a test detects disease when disease is present
- 100% = rule out disease & low false negative rate
- TP/ (TP+FN)
- high Sensitive test when Negative, rules out disease
Specificity
True Negative rate
- Proprotion of all people without disease who test negative
- probability that a test indicates non-disease when disease is absent
- Value approaching 100%= desirable for ruling IN disease (low false positive)
- TN/ (TN +FP)
- Specific Test when Positive, rules IN disease
Positive predictive value
Proprotion of positive test results that are true positive
- Probability that person actually has the disease given a positive test result
- TP/ (TP+FP)
- high pretest probability–> high PPV
Negative Predictive value
Proprotion of negative test results that are true negative
- proprotion that person actually is disease free given a negative test result
- TN/ (FN+TN)
- high pre-test probability–> low NPV
Incidence vs Prevalence
- Incidence: looks at NEW cases
- # new cases/ population at risk
- Prevalence: looks at all CURRENT cases
- # existing cases/ population at risk
Odds Ratio
Odds that the group with the disease was exposed to a risk factor divided by the odds that the group without the disease (control) was exposed
- Used in case control study
Relative Risk
Risk of deeloping disease in the exposed group divided by risk in the unexposed group
- typically used in cohort study
- if prevalence is low, RR= OR
Relative Risk Reduction
Proportion of risk reduction attributable to the intervention as compared to a control.
- RRR=1-RR
Absolute Risk reduction
Difference in risk (not proportion) attributable to the intervention as compared to a control
Attributable Risk
Difference in risk between exposed and unexposed groups, or the proportion of disease occurances that are attributable to the exposure
Number needed to treat
Number of patients who need to be treated for 1 patient to benefit
- 1/ (absolute risk reduction)
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)
Precision
- Precision: consistency and reproducibility of a test (reliability)
- absence of random variation
- random error reduces precision in a test
- increased precision= decreased standard deviation
Accuracy
Trueness of test measurements
- absence of systematic error or bias in a test
- Systematic error: reduces accuracy in a test
Selection Bias
Nonrandom assignment to participate in a study group
- Berkson bias: study looking only at inpatients
- Loss to follow up: studying a disease with early mortality
- Healthy workers and volunteer bias: study populations are healthier than general public
Reduce bias
- Randomization
- Ensure choice of right comparison group
Recall Bias
Awareness of disorder alters recall by subject
- common in retrospective studies
- Strategy to reduce bias: decrease time from exposure to follow up
Measurement Bias
Information is gathered in a way that distorts it
- Hawthorne effect: groups who know they are being studied behave differently
- Reduce bias: use placebo control groups with blinding to reduce influence of participants
Procedure Bias
Subjects in different groups are not treated the same
Observer expectancy bias
researcher’s belief in efficacy of a treatment changes the outcome of treatment
Confounding bias
When a factor is related to both the exposure and outcome, but not on the causal pathway
- factor distorts or confuses effect of exposure on outcome
- Strategy to reduce bias: multiple/repeat studies, cross-over studies, matching studies
Lead time bias
Early detection is confused with increase in survival
- early detection makes it seen as though survival has increased but natural history of disease has not changed
- Strategy to reduce bias: measure “back-end” survival (adjust survival according to severity at time of disease)
Measure of central tendancy
- Mean: sum of values/total number of values
- Median: middle value of a list sorted from least to greatest
- Mode: most common value
Measure of Dispersion
- Standard deviation: how much variability exists from mean in a set of values
- Standard error of the mean: estimation of how much variability exists between the sample mean and true population mean
Normal Distribution
- Gaussian, bell shaped curve
- Mean=Median=Mode