Study Designs_YL


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  • Question – what r the study designs you know of?
  • Research question will be followed desc by my colleague
  • For this session we will discuss some of the most commonly used study designs
  • More than 2 contacts regular interval but can vary from weeks, months, year Longer period Info gathered each time is identical Data from Same study population but NOT necessary same respondent
  • Study Designs_YL

    1. 1. Study Design Yvonne Lee Yin Leng, MPH Clinical Epidemiology Unit, CRC
    2. 2. Study design
    3. 3. Common study design <ul><ul><ul><ul><li>Randomized controlled trial </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Cohort study </li></ul></ul></ul></ul><ul><ul><ul><ul><li>3. Case control study </li></ul></ul></ul></ul><ul><ul><ul><ul><li>4. Cross sectional study </li></ul></ul></ul></ul><ul><ul><ul><ul><li>5. Ecologic or trend study </li></ul></ul></ul></ul><ul><ul><ul><ul><li>6. Case report or case series </li></ul></ul></ul></ul><ul><ul><ul><ul><li>7. Qualitative research </li></ul></ul></ul></ul>
    4. 4. Purpose different study design <ul><li>Different purpose / objective of the study </li></ul><ul><li>Maximizing study validity, in particular minimizing biases (Validity –accuracy, ability to give a true measure, i.e. measure what it purports to measure) </li></ul><ul><li>Increase reliability </li></ul><ul><li>  </li></ul><ul><li>Reliable, invalid Unreliable, invalid Reliable, valid </li></ul>
    5. 5. Which study design? <ul><li>Research questions </li></ul><ul><li>Objective of the study </li></ul><ul><li>Occurrence of disease / exposure -rare/ common </li></ul><ul><li>Ethical issue </li></ul><ul><li>Resources- money, manpower, machine </li></ul><ul><li>Several designs may well be suitable for a </li></ul><ul><li>particular study. Choice must then be guided by </li></ul><ul><li>considerations of strength of design, cost and ethics. </li></ul>
    6. 6. Research question <ul><li>Why, what, when, where, who, how ? </li></ul>P atient Doctor Diagnosis/Cause Treatment Outcome Medical death Death Cure Surgical cure Chronic Rehabilation Group of Patients’ Trend Community -burden
    7. 7. Randomized controlled trial <ul><li>Evaluate new forms of therapy and prevention </li></ul><ul><ul><li>Treatment - drug </li></ul></ul><ul><ul><li>Health care technology - device </li></ul></ul><ul><ul><li>Methods of primary prevention - screening </li></ul></ul><ul><ul><li>Organizing and delivering health services (community trial) </li></ul></ul><ul><ul><li>Impact of new policies in health care and health care financing (community trial) </li></ul></ul>
    8. 8. Randomized controlled trial <ul><li>Strongest design - randomization, minimize selection bias </li></ul><ul><li>Must be ethical - no harmful intervention, no poor clinical outcome </li></ul><ul><li>Difficult for intervention in rare disease / rare outcome </li></ul><ul><li>Participation of subjects is crucial </li></ul>
    9. 9. <ul><li>Elements Design </li></ul><ul><li> Randomization </li></ul>Randomized controlled trial New treatment Current treatment/ no treatment Improved Not improved Improved Not improved Intervention Outcome Selection of subjects -similar features -inclusion/exclusion criteria Allocation of subjects Data collection Masking (blinding) Define population
    10. 10. Type of randomized clinical trials Surgical Medical randomized randomized Refuse surgery Require surgery No surgery Surgery <ul><li>Most common </li></ul><ul><li>Parallel A </li></ul><ul><li>B </li></ul><ul><li>Cross-over </li></ul><ul><li>Planned – wash out </li></ul><ul><li>Unplanned </li></ul>
    11. 11. Randomized controlled trial <ul><li>Blinding </li></ul><ul><ul><li>Single – subjects (placebo effect) </li></ul></ul><ul><ul><li>Double - subjects & investigators </li></ul></ul><ul><ul><li>Triple blind - subjects & investigators & statisticians </li></ul></ul><ul><li>Outcome/endpoint </li></ul><ul><ul><li>Improvement ( desired effect) and side effects </li></ul></ul><ul><ul><li>Must be explicitly defined </li></ul></ul><ul><ul><li>Measured comparably in all study groups </li></ul></ul><ul><li>Multi-center trial </li></ul><ul><li>Comply with CPG requirements </li></ul><ul><li>Results of RCT- benchmark of clinical practice guideline (CPG), clinical governance, treatment protocol </li></ul>
    12. 12. Randomized controlled trial <ul><li>Absolute risk factor = Rate in unRx- Rate in Rx </li></ul><ul><li>Efficacy (Relative Risk Reduction) </li></ul><ul><li>= Rate in unRX - rate in RX </li></ul><ul><li>Rate in UnRX </li></ul><ul><li>Number Needed – to – Treat (the number of patients who have to be treated to prevent one outcome event) </li></ul><ul><li>= 1 </li></ul><ul><li>Rate in unRX- Rate in RX </li></ul>
    13. 13. Randomized controlled trial <ul><li>? Effective in uncontrolled community </li></ul><ul><li>Consent refusal - automatic selection </li></ul><ul><li>(people who participate are different from those who do not) </li></ul><ul><li>Non-compliance (people who complaint are very different from those who are not) </li></ul><ul><li>Drop-out: not adherence to experimental regimen, loss to follow-up </li></ul><ul><li>Drop-in: not adherence to control regimen </li></ul><ul><li>Compliance -Need monitoring </li></ul><ul><li>Most costly </li></ul>
    14. 14. Observational studies <ul><li>Cohort study </li></ul><ul><li>Case-control study </li></ul><ul><li>Cross sectional study </li></ul><ul><li>Ecologic or trend study </li></ul><ul><li>Case report or series </li></ul><ul><li>Qualitative research </li></ul><ul><ul><ul><ul><li>Direction, timing, +/- control </li></ul></ul></ul></ul>
    15. 15. Cohort study Exposed Disease Future Now Not Exposed No Disease Disease No Disease Association Historical data Concurrent data 1970 2005 2010 2005 2010
    16. 16. When is a cohort study warranted ? <ul><li>Subset of defined population starting with e xposed / non-exposed and follow-up to determine occurrence of outcome </li></ul><ul><li>Exposure is rare and incidence of disease among exposed is frequent </li></ul><ul><li>Time between exposure and disease is short </li></ul><ul><li>Measure Incidence </li></ul><ul><li>Advantage </li></ul><ul><ul><li>Can see temporal cause and effect relationship (causality) </li></ul></ul><ul><li>Disadvantage </li></ul><ul><ul><li>Longer waiting time for outcome </li></ul></ul><ul><ul><li>Loss to follow up </li></ul></ul><ul><ul><li>Potential bias </li></ul></ul><ul><ul><li>Exposure changes over time (i.e. lifestyle: diet, smoking pattern) </li></ul></ul>
    17. 17. Cohort study Disease (+) Exposed (+) Exposed (-) Disease (-) Total Incidence rate of disease a b c d a + b c + d a/a+b c/c+d
    18. 18. Case control study Exposed Disease In the past Now No disease Not Exposed Exposed Not Exposed Case Control Non-randomized
    19. 19. Case control study <ul><li>Control group sampling </li></ul><ul><li>Hospital control- convenient but bias </li></ul><ul><li>Non-hospital control </li></ul><ul><li>Probability sample of total population </li></ul><ul><ul><li>Neighborhood </li></ul></ul><ul><ul><li>Best friends or associates </li></ul></ul><ul><ul><li>Spouse or sibling </li></ul></ul><ul><ul><li>Birth cert match or classmate (childhood diseases) </li></ul></ul><ul><li>Matching – the process of selecting controls who are similar to cases in regard to certain characteristics e.g. age, sex, race. </li></ul>
    20. 20. When is a case control warranted? <ul><li>A study comparing persons with a given condition or disease (cases) and persons without the condition or disease (controls) </li></ul><ul><li>Disease is rare and exposure is frequent among exposed </li></ul><ul><li>Study association of a disease with several exposures or factors </li></ul><ul><li>Advantage </li></ul><ul><ul><li>Cost - cheaper </li></ul></ul><ul><ul><li>May study past exposure and current effect – shorter waiting time </li></ul></ul><ul><li>Disadvantage </li></ul><ul><ul><li>Recall bias (Case may remember more than control) </li></ul></ul><ul><ul><li>Selection of appropriate control </li></ul></ul>
    21. 21. Case control study Disease (+) Exposed (+) Exposed (-) Disease (-) Total a b c d a + b c + d Odd ratio = a/a+c = ad b/b+d bc Proportion of exposed a a+c b b+d
    22. 22. Cross sectional study <ul><li>Prevalence surveys measure exposure and effect at the same point in time </li></ul><ul><li>Describe prevalence and distribution of heath problem in a community (etc. health survey) </li></ul><ul><li>In clinical research, use in describing disease presentation (spectral description study), diagnostic test accuracy study, quality of care assessment, market survey </li></ul><ul><li>Limitation </li></ul><ul><li>Expensive </li></ul><ul><li>Data may give false causal interpretation (pseudo-longitudinal) </li></ul>
    23. 23. Ecologic or trend study <ul><li>Group based study, unit of observation is a group e.g. cancer mortality in a country, state </li></ul><ul><li>Ignore variability between individuals </li></ul><ul><li>Aggregation bias- association observed at group level and not at individual level (ecological fallacy) </li></ul>
    24. 24. Case report or case studies <ul><li>Description of one or several cases in which no attempt is made to answer specific hypotheses or to compare results with another group of cases </li></ul><ul><li>No control </li></ul><ul><li>Classical clinical study </li></ul><ul><li>Its value probably under rated </li></ul>
    25. 25. Qualitative study <ul><li>Development of concepts which help us to understand social phenomena in natural settings, giving due emphasis to the meanings, experiences, and views of all the participants </li></ul><ul><li>Explaining complex phenomena not amenable to quantitative research </li></ul><ul><li>Method - Focus group, observation, interview, diary </li></ul><ul><li>Application </li></ul><ul><li>Doctor-patient relationship, treatment compliance, clinical decision making process, issues on health service organization and policy issues </li></ul>
    26. 26. Summary Design depends on research Q Treatment efficacy/safety – RCT Diagnostic methods – x section Prognosis- outcome - cohort Agreement measurement – X sectional Classification - cohort (outcome), X section (criteria)