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89 Cards in this Set
- Front
- Back
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Absolute Risk
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*incidence of disease in pop
*proportion of disease in pop *no comparison |
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Relative Risk
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*cohort studies
*measures incidence *measure strength of association *valuable in etiologic studies *proportion of diseased in exposed over proportion of diseased in non-exposed |
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Relative Risk
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= incidence exposed (a/a+b) / incidence not exposed (c/c+d)
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Odds Ratio
(Relative Odds) |
*Cohort and Case Control
*Measures prevalence *Odds of diseased in exposed over odds of diseased in non-exposed |
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Odds Ratio
for Cohort Study |
= (a/b) / (c/d)
or = (a)(d) / (b)(c) |
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Matched Pairs Odds Ratio
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The ratio of the number of pairs that support the hypothesis of an association (pairs in which the case was exposed and the control was not) to the number of pairs that negate the hypothesis of association (pairs in which the control was exposed and the case was not)
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When is the odds ratio obtained in a case-control study a good approximation of the relative risk?
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1.When the cases are representative, with regards to history of exposure, of all the people with the disease in the population.
2.When the controls studied are representative, with regards to history of exposure, of all the people without the disease in the population. 3.When the disease studied does not occur frequently. *a+b can be aprox by b *c+d can be aprox by d Frequency of disease is low in exposed and non-exposed |
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Difference in Risk
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(Disease risk in exposed) - (Disease risk in non-exposed)
(a/a+b)-(c/c+d) *not a useful ratio |
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Attributable Risk
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*How much of the disease that occurs can be attributed to a certain exposure?
*The amount of proportion of disease incidence (or disease risk) that can be attributed to a specific exposure *How much of the incidence can we hope to prevent if we can eliminate exposure? *Applications in clinical practice and public health *Attributable Risk in Exposed Group ** *Attributable Risk in Total Population |
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**Attributable Risk in Exposed Group
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(incidence in exposed group)-(incidence in nonexposed group)
/incidence in exposed group |
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**Attributable Risk in Total Population
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(incidence in total population) - (Incidence in nonexposed group)
/incidence in total population |
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Incidence in total population calculation
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(incidence in exposed)(% of exposed in population)
+ (incidence in nonexposed)(% of nonexposed in pop) |
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Cohort Studies
Retrospective and Prospective |
Exposed vs nonexposed
Incidence in exposed/Incidence in nonexposed Prospective determines temporal relationship between exposure and disease Retrospective hard to establish temporal relationships Can study association of an exposure with several diseases Prospective generally long and expensive Retrospective may be short and sometimes less expensive Large population needed Prospective bias in assessment of exposure and of outcome Best when exposure is rare and disease is frequent Problems - selection of comparison group and change in criteria and methods over time. |
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Case-Control
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- Persons with dz (cases): (a+c) vs persons without the dz (controls): (b+d)
- Proportion of cases exposed/proportion of controls exposed - Odds ratio, attributable risk - Sometimes hard to establish temporal relationship - Possible to study associations of a disease with several exposure factors - Relatively inexpensive and small population - Potential bias in assessment of exposure - Best when diseas is rare and exposure is frequent among the diseased Problems: selection of appropriate controls often difficult and incomplete information on exposure |
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Natural experiments
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The business of using groups of individuals exposed for nonstudy purposes as subjects for research to be compared to other groups that have not been exposed
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Ecologic Studies
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The first approach in determining whether an association exists
Study of group characteristics Scatterplot |
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Ecologic Fallacy
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Do not have individual information
No account is taken for the variability between individuals |
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Causal Relationship
- Necessary and Sufficient |
Without the factor the disease never develops (necessary)
In the presence of the factor the disease always develops (sufficient) very rare |
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Causal Relationship
- Necessary but not Sufficient |
Multiple factors are required to cause disease to develop
Factors often must occur in temporal sequence Cancer: initiator and promoter |
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Causal Relationship
- Sufficient but not Necessary |
Factor Alone can produce the disease
Not the only factor that can produce the disease Radiation or benzene exposure can cause leukemia |
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Causal Relationship
- Neither Sufficient nor Necessary |
By itself, factor is neither sufficient nor necessary to produce disease
More complex model, which probably most accurately represents the causal relationships that operate in most chronic diseases |
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Guidelines for Judging Causality
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1.Temporal relationship
2.Strength of Association 3.Dose-Response relationship 4.Replication of findings 5.Biologic plausibility 6.Consideration of alternate explanations 7.Cessation of exposure 8.Consistency with other knowledge 9.Specificity of the association |
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Temporal Relationship
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Exposure before disease
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Strength of Association
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Relative risk of odds ratio
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Risk Analysis
2.Dose-Response Relationship |
As the dose increases so does the risk, however does not rule out causality
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Replication of Findings
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Relationship apparent in different studies
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Biologic Plausibility
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Coherent with the current body of biologic knowledge
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Consideration of Alternate Explanations
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The extent to which investigators have taken other explanations into account and how rigorously they ruled them out.
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Cessation of Exposure
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Expect risk to decline when exposure to the factor is reduced or eliminated
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Consistency with other Knowledge
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Data consistency
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Specificity of the Association
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When a certain exposure is associated with only one disease; weakest of all guidelines
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Bias
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"any systematic error in the design, conduct or analysis of a study that results in a mistake estimate of an exposure's effect on the risk of a disease"
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Selection Bias
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- Study subjects are not representative of target pop
- Association perceived because of selection that in reality does not exist - Response rate higher in those with the disease - Generally people who respond differ from those who do not - Affects generalizability of external validity - Exclusion bias - researchers using past criteria for exclusion of case and controls |
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Information bias
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Occurs when the means for obtaining information about the subjects in the study are inadequate so that as a result some of the information gathered regarding exposures and/or disease outcome is incorrect
Misclassification bias |
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Missclassification bias
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Differential - the rate of misclassification differs in different groups
Nondifferential - results from the degree of inaccuracy that characterizes how information is obtained from any study group. Not related to case or control status. Problem inherent in data collection methods |
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Confounding
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Derivation of a causal relationship when there is not one
Factor X is a known risk factor for disease B Factor is associated with factor A, but is not a result of factor A Confounding causes the outcome Control for confounding -Stratification -Adjusted rates -Multivariate analysis |
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Interaction
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"When the incidence rate of disease in the presence of two or more risk factors differs from the incidence rate expected to result from their individual effects."
*Additive-the effect of one exposure is added to the effect of the second exposure *Multiplicative-multiplies relative risks of each exposure with each other Very common |
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Role of genetics and ENVR to Epidemiological Studies
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- Every study implicitly or explicitly asks how much of risk is attributable to genetics and how much is due to environmental factors
- Genetics is host aspect of triad - Genetic form typically develops earlier than nongenetic |
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Twin Studies
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- Test genetic factors
- Monozygotic/Identical/100% genetic material - Dizygotic/Fraternal/50% genetic material - Monozygotic most useful for study - Concordant - both have dz - Discordant - one has dz and other does not |
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Adoption Studies
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Study environment factors
Most ideal would be monozygotic adopted by separate families |
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Migrant Studies
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Individual migrants from low risk area to high risk area or vice versa
If incidence stays the same then genetic factors are at play if it changes to fit the new environment then genetics are playing less of a role Good test of genetics vs environment |
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Efficacy
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Does the agent work in the lab? Ideal conditions
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Migrant Studies
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- Individual migrants from low risk area to high risk area or vice versa
- If incidence stays the same then genetic factors are at play if it changes to fit the new environment then genetics are playing less of a role - Good test of genetics vs environment |
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Effectiveness
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Does the agent work in real life?
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Efficiency
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Can the agent work better?
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Efficacy
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Does the agent work in the lab? Ideal conditions
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Migrant Studies
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Individual migrants from low risk area to high risk area or vice versa
If incidence stays the same then genetic factors are at play if it changes to fit the new environment then genetics are playing less of a role Good test of genetics vs environment |
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Effectiveness
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Does the agent work in real life?
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Health Service Evaluation
- Group Data |
Important to be aware of the data source
Exclusion criteria varies and contributes to selection bias Self-selection bias |
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Efficiency
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Can the agent work better?
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Efficacy
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Does the agent work in the lab? Ideal conditions
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Health Service Evaluation
Group Data |
-Important to be aware of the data source
-Exclusion criteria varies and contributes to selection bias -Self-selection bias |
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Effectiveness
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Does the agent work in real life?
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Migrant Studies
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- Individual migrants from low risk area to high risk area or vice versa
- If incidence stays the same then genetic factors are at play; if it changes to fit the new environment then genetics are playing less of a role - Good test of genetics vs environment |
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Efficiency
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Can the agent work better?
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Health Service Evaluation
- Group Data |
Important to be aware of the data source
Exclusion criteria varies and contributes to selection bias Self-selection bias |
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Efficacy
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Does the agent work in the lab? Ideal conditions
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Effectiveness
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Does the agent work in real life?
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Efficiency
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Can the agent work better?
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Health Service Evaluation
- Group Data |
Important to be aware of the data source
Exclusion criteria varies and contributes to selection bias Self-selection bias |
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Health Service Evaluation
- Outcome Research |
- Mortality, morbidity, quality of life, functional status, patient perception of health status
- Large data sets - representative, generalizable - Large populations - Using existing data speeds up process - Cheaper - Needed measures may not be part of data since the instrument was not specifically developed for that purpose - Outdated data - Inconsistent coding - Must consider age of data and changes in procedures and knowledge since it was generated |
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Health Service Evaluation
- Individual Data |
- Usually preferable over group data
- Must ask two questions when comparing populations - Are the characteristics of the two populations comparable? - Are the Measurement methods comparable? |
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Health Services Evaluation
- Randomized Design |
Eliminates selection bias
Randomly chosen to receive one treatment or another Cohort randomized trial very effective but expensive |
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Health Services Evaluation
- Nonrandomized Design |
Before and after comparison of a new program
Program / No program Utilizers and non-utilizers comparison Eligible and non-eligible |
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Evaluation of Screening Programs
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Do the individuals in whom the disease is detected early benefit from the early detection, and is there an overall benefit to those who are screened?
Process or outcome evaluation |
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Bias
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- Selection bias
- Lead time bias - How much earlier can the diagnosis be made if the disease is detected by screening compared with the usual timing of the diagnosis if screening were not carried out? - Overdiagnosis bias - Due to enthusiasm individuals in the screened group are more likely to be erroneously diagnosed as positive than are normal individuals in the unscreened group |
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Evaluation of Screening Programs
- Study Design |
Nonrandomized
*Case-control - screened/not screened: is the disease present in both? Randomized *Population is randomized and divided into groups (screening and no screening) *Tough to carry out, ethical issues *Most screening programs are not randomized |
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Evaluation of Screening Programs
- Cost |
Includes financial and non-financial anxiety, emotional distress, inconvenience
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Evaluation of Screening Programs
Benefit |
- Can the disease be detected early?
- What is the cost? financial / emotional? - Seriousness of false positive results? - Are subjects harmed? - Overall benefit to being screened? - Use operational and outcomes measurements to assess effectiveness |
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Risk Analysis
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1. Hazard identification
2. Dose-response assessment 3. Exposure assessment 4. Risk Characterization |
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Hazard Identification
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Determination of whether a particular chemical is casually linked to particular health effects
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Risk Analysis
2. Dose-response Assessment |
Determination of the relationship between the magnitude of exposure and the probability of occurrence of the health effects in question
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Risk Anlysis
3. Exposure Assessment |
Determination of the extent of human exposure before or after application of regulatory controls
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Risk Analysis
4. Risk Characterization |
Description of the nature - and often magnitude - of human risk, including attendant uncertainty
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Risk Analysis
3. Exposure Assessment |
1. Interviews a. subject b. surrogate
2. Employment or other records 3. Physician records 4. Hospital records 5.Disease registry records (e.g. cancer registries) 6.Death certificates |
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Meta-Analysis
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"The statistical analysis of a large collection of analysis results from individual studies for the purpose of integrating the findings."
Aggregates the results from a set of studies, with appropriate weighting of each study for the number of subjects sampled and for other characteristics |
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Uncertainty
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Study design
Deficiencies in the conduct and implementation of the study Presentation and interpretation of study findings |
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Public Policy Issues
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1. What percentage of the population should be protected by the policy?
2. What level of risk is society willing to tolerate? 3. What level of control of risk is society willing to pay for? 4. Who should make decisions about risk? |
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Ethical Issues
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- Findings have direct and often immediate societal relevance
- Studies generally funded from public resources and have major implications for allocation of limited societal resources - Research involves human subjects, and subjects generally derive no personal benefit from the results of these studies |
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Obligation to Study Subjects
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- Truly informed consent - full discloser can create bias in the subject
- Assurance of confidentiality - Balancing the rights of the individual and the welfare of the society - Communicating study findings to subjects - the obligation of the investigator to help the subjects further their important legitimate interests, such as disease prevention and control, for themselves and their families |
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Confidentiality
- Medical Records Needed |
To generate aggregate data
To identify individual patients for subsequent follow-up |
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Confidentiality
- Legislative proposals |
Patient consent is required for medical records
No identifying information |
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Confidentiality
Problems: Patient consent |
o Record review for selection
Patients unavailable for consent Many patients refuse which then create selection bias in those included in the study |
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Confidentiality
Problems: No identifying information |
Record review for selection
Identifying information is essential in determining source of data |
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Confidentiality
- Epidemiologic Procedures |
- Informed consent required except review of medical records
- All data stored under lock and key - Case numbers assigned to forms - Identifying information destroyed at end of study - Results published in aggregate form - Unless necessary individual information not entered into computer files Importance of privacy emphasized to research staff |
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Confidentiality
- HIPAA |
- Health Insurance Portability and Accountability Act of 1996
- First systematic nationwide privacy protection for health information in the US - Allows for release of health information under certain conditions * IRB waiver *Preparatory to initiation of research *Research on decedent’s information |
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Access to Data
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- At what point has a study truly been completed
- Should sharing policy be dependent on who paid for study - Should policy depend on possible motivations of persons asking - Under what conditions should identifiers be included - How can the investigator’s interests be protected - Who will pay expenses |
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Conflict of Interest
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- Most US research conducted by individuals in academia, industry, or government
- Government and industry usually have internal funding - Academia rely heavily on outside funding through grants *Subject to rigorous peer review - Academia typically has less conflict/ no vested interest in results - Potential bias introduced by employer pressure |
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Interpreting and Communicating Findings
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How do we assess the importance of a single study that shows increased risk?
How many confirmatory studies are needed? Uncertainty *Should assist the public in dealing with uncertainty When does a trivial increase in risk ratio become a public concern? Must draw best conclusions based on available data fully realizing the possibility of future study Policy making *Generating and interpreting data *Presenting specific policy options *Projecting the impact of each decision *Developing specific policy proposals *Evaluating the effects of policies after they have been implemented Educator and researcher *Health professionals, legislators, lawyers, judges, public |
