Stat Flashcards
odds ratio<1
decreased risk
odds ratio=1
equal risk
odds ratio>1
increased risk
odds ratio= relative ratio
outcome is rare
to strengthen the argument for causality, consider (7)
consistency, plausibility, dose-response, temporality, strength of relationship, reversibility, lack of alternative explanations
types of descriptive studies (3)
detail one observation
ecologic study, case reports, case series
case reports
○ One or few patients
○ Link clinical medicine and public health
○ Publications and rounds
○ Rare disease/cases
case series
More than a few patients Good details CONS Small, highly selected group No hypothesis No comparison
Ecologic Study
Ecologic Study
○ Goal: comparing disease rates between population groups
○ Exposure (predictor or risk factor) —> disease (outcome or response)
○ “ecological correlation” or “aggregate risk” = exposure-outcome relationship
○ Suggests a link associated with a group
○ Ex) countries with higher fat diets = higher breast cancer rates
Ecologic Study: pros
Etiological hypothesis
Use to set research priorities
Low cost
Study large population
Studies hard to study environmental health questions
Ecologic Study: cons
No individual data
“ecological fallacy”
One could infer inappropriate individual relationship
**be careful not to over-interpret results
Analytical Study types (3)
cohort, case-control, cross-sectional study
Case-control study
*rare diseases
outcome –> exposure
○ Moves backwards in time
○ Find those with disease and look back at their exposure
○ Controls: from at risk population (had opportunity for exposure/disease), but free of disease at time
○ Odds ratio: estimates risk
Case-control study: pros
Study rare or long latency diseases
Requires few subjects
Faster, Less time
Evaluate multiple exposures (risks) as potential causes of disease
Case-control study: cons
Relies on subject’s recall for past exposures; biases
Difficult to select appropriate control group
Odds ratio only estimates relative risk
Cannot calculate incidence rates
Cross-sectional study
*quick measure
exposure and outcome at same time
○ “prevalence study”
○ Ex) who is more dissatisfied with weight: male or females?
Prevalence ratio
Cross-sectional study: pros
Good measure of disease prevalence What to expect in clinical setting Evaluate screening and diagnostic tests Help plan health services Quick- ask one question Easy Inexpensive
Cross-sectional study: cons
Measure disease/exposure at same time Cannot determine causality Cannot determine temporal relationship of exposure and disease Limited: study prevalence only Cannot determine disease incidence
Cohort study
*rare exposures
exposure—> outcome
○ Moves forward in time
○ Follow patients over time to see if they develop disease
○ Compare incidence of new development of disease
○ Ex)is physical fitness related to respiratory illness risk
assesses relative risk, attributable risk
Cohort study: pros
An evaluate multiple outcomes
Provide actual measure of risk of outcome
Can extract incidence and relative risk
Approximates Random control design
Cohort study: cons
Potential loss for follow-up
Needs large number of subjects
Takes a long time- not efficient to wait for outcome
Expensive, lots of staff
Randomized clinical trial
*best evidence Experimental Study • Randomly assign participants to one or two treatments • Produce comparable, similar study groups (equal known/unknown risk factors) • Removes investigator bias by allocating participants randomly • Valid statistical tests • Comparison groups: ○ No intervention ○ Observation- Hawthorne effect ○ Placebo ○ Usual care • Blinding/ masking
define: correlation
measures strength of association btwn 2 variables
define: regression
method for relating predictor to outcome
