research design fw 2011
DESCRIPTION
A brief overview of epidemiological research designs as well as survey construction.TRANSCRIPT
Comparing Research DesignsTiffany Smith, Eric Heidel, &Patrick BarlowResearch and Statistical Design Consultants
Comparing Research Designs Cohort Studies
Case Control Studies
Cross-Sectional Studies
Developing Survey Instruments
Cohort Studies A “cohort” is a group of individuals
who are followed or traced over a period of time.
A cohort study analyzes an exposure/disease relationship within the entire cohort.
Cohort Design
Prospective versus Retrospective Cohort Studies
Exposure Outcome
Prospective Assessed at the beginning of the study
Followed into the future for outcome
Retrospective
Assessed at some point in the past
Outcome has already occurred
Advantages and Disadvantages of Cohort Studies
Advantages• Establish population-based
incidence• Accurate relative risk• Examine rare exposures• Temporal relationship
inferred• Time-to-event analysis
possible• Used when randomization
not possible• Quantifiable risk magnitude• Reduces biases (selection,
information)• Can study multiple outcomes
Disadvantages• Lengthy and costly• May require very large
samples• Not suitable for rare/long-
latency diseases• Unexpected environmental
changes• Nonresponse, migration and
loss-to-follow-up• Sampling, ascertainment
and observer biases• Changes over time in
staff/methods
Case-Control Studies A sample with the disease from a
population is selected (cases).
A sample without the disease from a population is selected (controls).
Various predictor variables are selected.
Strategies for Sampling Controls Hospital- or clinic-based controls Matching Using a population-based sample of
cases Using 2 or more control groups
Advantages and Disadvantages of Case-Control Studies
Advantages High
information yield with few participants
Useful for rare outcomes
Disadvantages Cannot estimate
incidence/prevalence of disease
Limited outcomes can be studied
Highly susceptible to biases
For Discussion “How much does a family history of
lung cancer increase the risk of lung cancer?” The PI plans a case-control study to answer this question. How should she pick the cases? How should she pick the controls? What are some potential sources of
bias in the sampling of cases and controls?
Cross-Sectional Studies• “Snapshot” of a population.• Cross-sectional studies include surveys.• People are studied at a “point” in time,
without follow-up.• Data are collected all at the same time
(or within a short time frame).• Can measure attitudes, beliefs,
behaviors, personal or family history, genetic factors, existing or past health conditions, or anything else that does not require follow-up to assess.
• The source of most of what we know about the population.
Advantages and Disadvantages of Cross-Sectional Studies
Advantages Fast and
inexpensive No loss to follow-up Springboard to
expand/inform research question
Can target a larger sample size
Disadvantages Can’t determine
causal relationship
Impractical for rare diseases
Risk for nonresponse
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INSTRUMENTATION RESULTS
Junk In Junk Out
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Steps in Assembling the Instruments for the Study
1. Identify the purpose and focus of study2. Obtain feedback from experts to clarify the
purpose and focus3. Identify the research methodology and type
of instrument to use for data collection4. Begin to formulate questions or items5. Pretest items and preliminary draft6. Revise instrument based on feedback7. Pilot test and revise8. Administer final instrument and analyze
and report results
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Reliability & Validity (Colton & Covert, 2007)
Validity: The extent to which we measure what we purport to measure (synonyms: accuracy). Types: Face, Concurrent, Predictive, Convergent,
Discriminant
Reliability: The extent to which an instrument produces the same information at a given time or over a period of time (synonyms: stable, dependable, repeatable, consistent, constant, regular). If the instrument is reliable, we would expect a patient who receives a high score
the first time he/she completes the instrument to receive a high score the next time he/she completes it (all things being equal).
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Parts of a Survey Title Introduction Directions or instructions Items Demographics Closing section
How to Create Survey Items (Colton & Covert, 2007)Literature reviewUse of existing processesBrainstormingSnowballing or pyramidingDelphi technique
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Strategies for Writing Good Items Avoid Double-barreled questions Appropriate readability
Sentence length Simple Language Clear, specific terminology
Exhaustive response sets Provide instructions for questions Culturally appropriate Sensitive items
Social desirability Avoid bias Limit negatively worded items Don’t include superfluous items
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Modes of Administration Post Mail Internet/Email Telephone Group Administration One-on-one/Interview
A response rate of 50-60% is often considered an acceptable return rate for survey research.
Sources of Error Sampling Error: A result of the measuring a
characteristic in some, but not all, of the units or people in the population of interest. Reduced by larger samples.
Coverage Error: The sample drawn fails to contain all the subjects in the population of interest.
Measurement Error: Error exists in the instrument itself (i.e. not valid and/or reliable).
Nonresponse Error: The inability to obtain data for all questionnaire items from a person in the sample population Unit/total Nonresponse Item Nonresponse
How to Increase Response Rate Know your population of interest Pre-Incentives
Preferably monetary Post-Incentives
Raffle/random give away Cognitive dissonance Electronic format Cover letters
Attending physicians rather than residents/fellows Clear informed consent
Not coercive Not forced
Follow-up emails Pre-survey emails
Material Learned Cohort Studies
Case Control Studies
Cross-Sectional Studies
Developing Survey Instruments
Questions?