Objectives Flashcards
Where are cohort and case-control studies in the hierarchy of evidence?
Best --> Worst Meta-analysis Systemic reviews Critically appraised sources RCTs Cohort Case control Case reports Expert opinion
What are the types of cohort studies?
Prospective (study starts at the exposure)
Retrospective (study starts after disease progression)
Ambidirectional (study starts at the beginning of the disease after exposure)
What are the types of cohorts?
Closed
Fixed
Open
What is a closed cohort?
Group followed from start tp pre-defined time end
People cannot enter or leave
What is a fixed cohort?
When follow-up time is same for all group members
What is an open cohort?
People can enter or leave cohort over chosen time-frame
What is cohort exposure?
Can vary based on levels/doses
Can also select non-exposed group separately, but must be as equivalent to exposed as possible
What are cohort outcomes?
ECHO
What does ECHO stand for?
Economic (Direct and indirect costs)
Clinical (A1c, asthma control, BP)
Humanistic outcomes (QoL, satisfaction w/care)
What is a case-control study?
Retrospective
Both cases and controls look back at the exposed and unexposed groups
In a case-control study, what results are we looking for?
Physical
Pathological
In a case-control study, why is accuracy important?
Do not want to include false positives
Be as restrictive as possible
In a case-control study, where does study information come from?
Hospital records Clinic patient rosters Death certificates Cancer registries Birth registries
In a case-control study, what are the types of cases?
Incident cases
Prevalent cases
What are incident cases?
New cases
If interested in causes of disease
What are prevalent cases?
Old cases
If wanting to know about factors affecting duration
In a case-control study, what are controls?
Sample of population that produced cases (study base)
What is a good control?
Members of the controls would be a case if they developed the condition
What are sources of controls?
Population
Hospital/clinic
Friend/spouse/relative
What should the ratio of control to cases be?
1:1 - 1:4
What are the ways to analyze cohort studies?
Incidence rate
Risk ratio
Risk difference
Odds ratio
What is an incidence rate?
Rate of incidence in both exposed and unexposed groups
What is a risk ratio?
Ratio of incidence rates in both the exposed and unexposed groups (a/a+b)/(c/c+d)
What does a risk ratio of 1 mean?
No difference
What does a risk ratio > 1 mean?
Increased risk
What does a risk ratio of < 1 mean?
Decreased risk
What is risk difference?
Exposed minus the unexposed rates
What is an odds ratio?
Represents the odds that an outcome will occur given a particular exposure compared to the odds of the outcome occurring (a/b)/(c/d)
What is an experiment?
Series of observations made under conditions controlled by scientists
What is a randomized experiment?
Experiment in which units assigned to receive treatment by random process
What is an observational study?
Simply observes size and direction of relationship among variables
What is random sampling?
Makes a sample of subjects similar to a population
What is a random assignment?
Makes sample of subjects similar to each other
What are institutional review boards (IRBs)?
Required for institutions who experiment on humans
Reviews study protocol to ensure Belmont report adhered to
What is a type I error?
Finding association when there is not
False positive
What is a type II error?
Finding an association when there is
False negative
What is an alpha error?
Type I error
Same as p-value
Usually findings < 0.05 are significant
What is a beta error?
Type II error
How is power calculated?
1-beta
Usually set at 20% (80% power)
What is representative sampling?
Sample that looks like population
What are types of representative samples?
Random
Stratified random
What is random sampling?
Potential subjects have non-zero chance of being selected
Requires access to everyone in population
What is stratified random sampling?
Perform random sample of individuals based on a certain set of characteristics
What are non-representative sampling?
Most common type of sample, convenience sample
What are types of non-representative sampling?
Purposively sample:
Non-random
Only selects people with a defining characteristic
What are the types of observational studies?
Cross-sectional
Quasi-experimental
What is a cross-sectional study?
Gather info at 1 point in time (cross-section)
Descriptive
Can measure prevalence well
Associations b/n DV and IV
Which observational study can identify causal relationships?
Quasi-experimental
What is a quasi-experimental study?
Treatment controlled by researcher
Subjects not randomly assigned to treatment
Which observational study has high internal validity?
Quasi-experimental
What do quasi-experimental studies need to infer causation?
More data than RCTs
More assumptions in analysis to infer causation
What is bivariate analyses?
Measures association between 2 variables of interest
What is multivariate analyses?
Measures association between a DV and IVs
What is the most common type of statistical analyses?
Paramteric
What are the most common types of parametric statistics?
Mean SD Correlation T-test ANOVA Linear regression
What assumptions are made in parametric statistics?
Variable is quantitative
Linear relationship b/n DVs and IVs
Normality of error distribution
What type of statistics has a DV that is normally distributed?
Parametric statistics
What are types of non-parametric statistics?
Chi-squared Fisher's exact Kruskal Wallis Wilcoxon Mann Whitney Spearman Friedman Logistic regression
What is nominal data?
Used for labeling variables, without any quantitative data (nominal sounds like name)
What are examples of nominal data?
Color
Sex
Location
What is dichotomous data?
Data with only 2 categories
Yes/no
Male/female
What is ordinal data?
The order of the data is important, but the difference between the values is not
What are examples of ordinal data?
How do you feel? (Okay, happy, very happy)
What is interval data?
Numeric scales in which we know the order and exact difference between the values
What is an example of interval data?
Temperature
What is ratio data?
Tells us about the order, the exact value between units, AND has an absolute zero
What are examples of ratio data?
Ht
Wt
What are the 3 pieces of cost determinants?
Identification
Measurement
Valuation
What are types of hospital costing?
Micro-costing
Case-mix group (accounts for LOS)
Disease specific per diem (daily cost)
Per diem (mean daily cost for all patients)
What is the most precise type of hospital costing?
Micro-costing
What is the least precise type of hospital costing?
Per diem
What are the tangible costs of pharmacoeconomic analyses?
Direct medical costs
Direct non-medical costs
Indirect costs
What are direct medical costs and benefits?
Medications Medication monitoring Medication administration Patient counseling and consultations Diagnostic tests Hospitalizations Clinic visits ED visits Home medical visits Ambulance services Nursing services
What are direct non-medical costs?
Travel costs to receive health care
Nonmedical assistance related to condition
Hotel stays for patient or family for out-of-town care
Child care services for children of patients
What are indirect costs and benefits?
Lost productivity for patient
Lost productivity for unpaid caregiver
Lost productivity because of premature mortality
What are intangible costs and benefits?
Unquantifiable costs and benefits
Improved health after treatment
Reduced pain
Pain and suffering associated with treatment
What are short-term tracking of costs and outcomes?
Hospital to d/c
What are medium-term tracking of costs and outcomes?
Payer
1-5 years
What are long-term tracking of costs and outcomes?
Patients
Life-time
What are the outcomes of CMA?
Assumed to be equivalent
What are the outcomes of CEA?
Natural units (life years saved)
What are the outcomes of CBA?
$
What are the outcomes of CUA?
QALY
What are the questions answered by CBA?
Which programs should be implemented
How much or what combination of outputs should be produced
What are the methods of measuring CBA?
Human capital
Willingness to pay
What is the simplest evaluation?
CMA
How is CMA used?
Compares 2+ alternative treatments that produce equivalent outcomes
Choose option with lowest cost
What is net benefit?
Total benefit - total costs
What benefit:cost ratio is preferred?
> 1
What does ICER stand for?
Incremental cost-effectiveness ratio
When are interventions said to be cost effective?
Less expensive AND more effective
Less expensive AND at least as effective
More expensive AND more effective
When is an ICER positive?
New tx more expensive AND more effective
New tx less costly AND less effective
Want smaller ICER
When is an ICER negative?
New tx less costly AND more effective
New tx more costly AND less effective
When is an ICER dominant?
Less costly AND more effective
When is an ICER dominated?
More costly AND less effective
What is a type of CEA?
CUA
What is QALY?
Combination of quantity life gained (mortality)
AND
Quality of the life gained (morbidity)
How do we measure quality of life gained?
Scale from 0 (death) - 1 (perfect health)
What are the disadvantages of a CUA?
Most difficult
Most time consuming
Most expensive
What are the ways to estimate utilities?
Visual analog scale (VAS)
Standard gamble (SG)
Time Trade-Off (TTO)
What is the VAS?
Easiest method to directly obtain utilities
What is a standard gamble?
Based on utility theory
2 alternatives
What is TTO?
Simpler, easier to use then SG
Subject offered 2 alternatives and they get to choose
What is a latent variable?
An unobservable phenomenon that takes on a specific value under a set of conditions
What are examples of latent variables?
Trust in physicians
QoL
Health literacy levels
What is reliability?
Proportion of variance attributable to the true score of the latent variable
What is a true score?
A scale developed to measure a latent variable is intended to estimate its actual magnitude at the time and place of measurement for each subject
What does reliability measure?
Same result
What are the types of validity?
Content validity
Criterion-related validity
Construct validity
What question does validity answer?
Is the latent variable the underlying cause of item covariation
What is content validity?
Extent to which a set of items reflects content domain
When does a scale have content validity?
When items are a randomly chosen subset of the universe of appropriate items
What is criterion-related validity?
Scale related to a gold standard
Also called predictive validity
What does construct validity measure?
Measures theoretical relationship of a variable to other variables
What are the two ways to measure self-reported HRQoL?
Generic
Disease specific
What are advantages of generic HRQoL?
Broadly applicable
Summarizes a range of concepts
May detect unanticipated effects
What are disadvantages of generic HRQoL?
May not be responsive to changes in health
May not be relevant for specific populations
Results may be difficult to interpret
What are advantages of disease specific HRQoL?
More relevant for specific populations
More responsive to changes in health
What are disadvantages of disease specific HRQoL?
Cannot compare across populations
Less likely to detect unanticipated effects
