Final Study Design ppt
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STUDY DESIGN
Study DesignObjectivesObjectivesBy the end of this session candidates By the end of this session candidates
should be able to: should be able to: 1. Review the fundamental study designs
2. Discuss Studies
-Uses -Strengths/weaknesses
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Most problems in studies are due to poor design (not poor analysis)
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Research Design
• The research design is the master plan specifying the methods and procedures for collecting and analyzing the needed information.
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Study Design
Experimental• Randomized controlled trials• Quasi
Observational
Analytic • Cross sectional• Case-control• Cohort studies
Descriptive• Case report• Case series• Survey
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Epidemiologic Study Designs
Experimental Observational
DescriptiveAnalytical
Case-Control Cohort
+ cross-sectional & ecologic
(RCTs)
Quasi
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Analytical Studies
Observational
Experimental
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Observational Studies
Cross-sectional
Case-control
Cohort
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Epidemiologic Study Designs
Grimes & Schulz, 2002 (www)
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Hierarchy of Epidemiologic Study Design
Tower & Spector, 2007 (www)
Cross-sectional Study
Data collected at a single point in
time
Describes associations
Prevalence A “Snapshot”
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Example of a Cross-Sectional Study
Association between garlic
consumption and CAD in the Family
Practice Clinic
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Cross-Sectional Study
Strengths Quick Cheap
Weaknesses Cannot establish cause-effect
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Observational Studies
Case-Control Study
Start with people who have disease
Match them with controls that do not
Look back and assess exposures
* case-control (retrospective ): Begins with outcome (cancer cases
and healthy controls
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Example of a Case-Control Study
Are those with CAD less likely to
have consumed garlic?
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Advantages of Case-Control StudiesAdvantages of Case-Control Studies
- Cheap, easy and quick studies
- Multiple exposures can be examined
- Rare diseases and diseases with long latency can be studied
- Suitable when randomization is unethical (alcohol and pregnancy outcome)
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Disadvantages of Case-Control StudiesDisadvantages of Case-Control Studies
- Case and control selection troublesome
- Subject to bias (selection, recall, misclassification)
- Direct incidence estimation is not possible
- Multiple outcomes cannot be studied
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Case-Control Studies: Strengths Good for rare outcomes: cancer Can examine many exposures Useful to generate hypothesis Fast Cheap Provides Odds Ratio
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Case-Control Studies: Weaknesses Cannot measure
Incidence Prevalence Relative Risk
Can only study one outcome High susceptibility to bias
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Design pitfalls to look out for
Care should be taken to avoid confounding, which arises when an exposure and an outcome are both strongly associated with a third variable.
Controls should be subjects who might have been cases in the study but are selected independent of the exposure.
Cases and controls should also not be "over-matched."
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Is the control group appropriate for the population? Does the study use matching or pairing appropriately to avoid the effects of a confounding variable? Does it use appropriate inclusion and exclusion criteria?
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Real-life Examples
Chambers, C. D., Hernandez-Diaz, S., Van Marter, L. J., Werler, M. M., Louik, C., & Jones, K. L. et al. (2006). Selective serotonin-reuptake inhibitors and risk of persistent pulmonary hypertension of the newborn. New England Journal of Medicine, 354(6), 579-587.
This study used a matched design, matching infants who had persistent pulmonary hypertension with infants who did not have it, and compared the rates of exposure to SSRIs. 04/08/23 22research design/ hanan abbas
Smedby, K. E., Hjalgrim, H., Askling, J., Chang, E. T., Gregersen, H., & Porwit-MacDonald, A. et al. (2006). Autoimmune and chronic inflammatory disorders and risk of non-hodgkin lymphoma by subtype. Journal of the National Cancer Institute, 98(1), 51-60.
This study matched patients with non-Hodgkin lymphoma (NHL) with control subjects and compared their history of autoimmune and chronic inflammatory disorders, markers of severity, and treatment. It found that the risk of NHL was increased in association with rheumatoid arthritis, primary Sjögren syndrome, systemic lupus erythematosus, and celiac disease.T
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Cohort Study
Begin with disease-free patients
Classify patients as
exposed/unexposed
Record outcomes in both groups
Compare outcomes using relative risk
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Example of a Cohort Study
To see the effects of garlic use
on CAD mortality in a population
cohort (prospective): Begins with an exposure (smokers and non-smokers)
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Examples of Cohort Studies
* Framingham Heart Study (www)
* NHANES Studies (www)
* MACS (www)
* Physicians' Health Study (www)
* Nurses' Health Study (www)
* ALSPAC (www)
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Advantages of Cohort Studies
- Can establish population-based incidence
- Accurate relative risk (risk ratio) estimation
- Can examine rare exposures (asbestos > lung cancer)
- Can be used where randomization is not possible
- Magnitude of a risk factor’s effect can be quantified
- Selection and information biases are decreased
- Multiple outcomes can be studied (smoking > lung cancer, COPD, larynx cancer)
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Disadvantages of Cohort Studies
- Lengthy and expensive
- May require very large samples
- Not suitable for rare diseases
- Not suitable for diseases with long-latency
- Unexpected environmental changes may influence the association
- Non-response, migration and loss-to-follow-up biases
- Sampling, and observer biases are still possible
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Cohort Study: Strengths
Provides incidence data
Establishes time sequence for causality
Eliminates recall bias Allows for accurate measurement of
exposure variables
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Cohort Study: Strengths
Can measure multiple outcomes
Can adjust for confounding variables
Can calculate relative risk
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Cohort Study: Weaknesses
Expensive
Time consuming
Cannot study rare outcomes
Confounding variables
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Cohort Study: Weaknesses
Exposure may change over time
Disease may have a long pre-clinical
phase
Attrition of study population
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Design pitfalls to look out for
Design pitfalls to look out for The cohorts need to be chosen from
separate, but similar, populations. How many differences are there
between the control cohort and the experiment cohort? Will those differences cloud the study outcomes?
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Real-life Example
Ramchand, R., Ialongo, N. S., & Chilcoat, H. D. (2007). The effect of working for pay on adolescent tobacco use. American Journal of Public Health, 97(11), 2056-2062.
This study uses data collected from high school students from Baltimore, Maryland, and studies the differences in initiation of tobacco use between a cohort of adolescents that started working for pay and a cohort of adolescents that did not work. The results suggest that adolescents who work for pay have a higher risk of initiating tobacco use.
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Lindenauer, P. K., Rothberg, M. B., Pekow, P. S., Kenwood, C., Benjamin, E. M., & Auerbach, A. D. (2007). Outcomes of care by hospitalists, general internists, and family physicians. New England Journal of Medicine, 357(25), 2589-2600.
To study effects of hospitalists, general internists, and family physicians on patient care, patients that were hospitalized with certain conditions under the care of hospitalists, general internists, and family physicians were separated into three cohorts. The results showed that patients cared for by hospitalists had shorter hospital stays and lower costs than those cared for by general internists or family physicians.
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Nichol, K. L., Nordin, J. D., Nelson, D. B., Mullooly, J. P., & Hak, E. (2007). Effectiveness of influenza vaccine in the community-dwelling elderly. New England Journal of Medicine, 357(14), 1373-1381.
To determine the long-term effectiveness of influenza vaccines in elderly people, cohorts of vaccinated elderly and unvaccinated community-dwelling elderly were studied. The results suggest that the elderly who are vaccinated have a reduced risk of hospitalization for pneumonia or influenza
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Experimental Studies
Clinical trials provide the “gold
standard” of determining the
relationship between garlic and
cardiovascular disease prevention.
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Clinical Trials
Randomized
Double-blind
Placebo-controlled
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Clinical Trials
Strengths: Best measure of causal relationship Best design for controlling bias Can measure multiple outcomes
Weaknesses: High cost Ethical issues may be a problem Compliance
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Experimental
Design
timeStudy begins here (baseline point)
Studypopulation
Intervention
Control
outcome
no outcome
outcome
no outcome
baselinefuture
RANDOMIZATION
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Types of trials
B lind ed N o t b lind ed
R a nd o m ised N o t ran d om ised
C o n tro lled N o t co n tro lled
T ria l
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Double-blind design• Neither patient nor outcome evaluator knows Rx to whichpatient was assigned• Single-blind• Patient or evaluator is blinded as to Rx, but not both• Triple-blind• Patient, Physician, and Data analyst are blinded as to Rxidentity
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Design pitfalls to look out for An RCT should be a study of one
population only. Was the randomization actually
“random,” or are there really two populations being studied?
The variables being studied should be the only variables between the experimental group and the control group.
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Müller, O., Traoré, C., Kouyaté, B., Yé, Y., Frey, C., Coulibaly, B., et al. (2006). Effects of insecticide-treated bednets during early infancy in an African area of intense malaria transmission: A randomized controlled trial. Bulletin of the World Health Organization, 84(2), 120-126.
The study done in this example was to determine whether the early use of bed nets had an effect on the morbidity rate of infants in rural Burkina Faso. An experimental group of infants used bed nets at birth, and a control group of infants used bed nets at six months of age. Results showed no significant difference in morbidity rates, but use of bed nets from birth was related to lower incidence of both malaria and moderate to severe anemia.
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Krishna, S., Balas, E. A., Francisco, B. D., & König, P. (2006). Effective and sustainable multimedia education for children with asthma: A randomized controlled trial. Children's Health Care, 35(1), 75-90.
This article reports on the effect of multimedia education for children with asthma. A control group of pediatric patients with asthma was given standard asthma educational resources, while the experimental group of pediatric patients with asthma was given standard resources plus multimedia resources. The study found a reduction in daily symptoms, in emergency room visits, in school days missed, and in days of limited activity in the group given multimedia education resources.
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Meta-Analyses
Systematic objective way to combine data from many studies
Pooled estimate of treatment effectiveness
Statistical significance Publication bias Theoretical framework Misleading results
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Systematic Reviews
Comprehensive survey All relevant studies of highest level
of evidence Rigorous analysis Systematic review
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Conclusion (1)
Case-series is a coherent set of cases of a disease (or similar problem).
Cases are compared with reference group, we have a case control study
In a population studied at a specific time and place (a cross-section) the primary output is prevalence data, though association between risk factors and disease can be generated.
In cross-sectional studies, we are looking for both exposure and outcome
In case-control studies, we know the outcome, looking for the exposure
In cohort studies, we know the outcome, following up looking for the outcome in question
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Conclusion (2)
If the population in a cross-sectional survey is followed up to measure health outcomes, this study design is a cohort study.
If the population of such a study are, at baseline, divided into two groups, and the investigators impose a health intervention upon one of the groups the design is that of a trial.
Studies based on aggregated data are commonly referred to as ecological studies.
Mostly, ecological studies are mode of analysis, rather than a design.
Interpretation and application of data are easier when the relationship between the population observed and the target population is understood
RCTs represent the “gold standard” of research designs. They thus provide the most convincing evidence of relationship between exposure and effect..
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What are the risk factors for the development of sarcoidosis?
What are the long-term effects of the daily use of topical minoxidil?
Scenario 3
Is there a difference between pediatricians and family
physicians in the practice of neonatal circumcision?
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Scenario 4
Does cigarette smoking cause lung cancer?
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