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Use of Whole Population Registers:

Use of Whole Population Registers:. Advantages and Disadvantages. Problems in Observational Studies. Who gets included? Who gets lost? How to ensure completeness of recruitment? How to standardise assessment? How to collect routinely gathered data fit for purpose?

Faraday
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Use of Whole Population Registers:

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  1. Use of Whole Population Registers: Advantages and Disadvantages

  2. Problems in Observational Studies • Who gets included? • Who gets lost? • How to ensure completeness of recruitment? • How to standardise assessment? • How to collect routinely gathered data fit for purpose? • Source of control group(s)?

  3. Threats • Internal validity • External validity

  4. Problem with:‘my clinical series’ • Who are your patients? • Which patients could you have included? • Which patients have you lost • And why?

  5. Issue of Catchment population Your area Your Clinic

  6. Issue of Catchment population Other clinics Your area Your Clinic

  7. Issue of Catchment population Your area Your Clinic Other Clinic

  8. Issue of Catchment population Your area Your Clinic Other Clinic ???

  9. Issue of Catchment population Your area Your Clinic ??? Other Clinic

  10. Does it matter • May or may not? • Selection factors related to: • Disease severity • Access • Costs • Education • Co-morbidity • Waiting time etc

  11. Who gets lost:The issue of left censorship

  12. Recruiting patients from clinic 2007 2001

  13. Recruiting patients from clinic: Attenders between January 2003 and December 2004 2007 2001

  14. Recruiting patients from clinic: Attenders between January 2003 and December 2004 2007 2001

  15. Recruiting patients from clinic: Attenders between January 2003 and December 2004 2007 2001

  16. Recruiting patients from clinic: Attenders between January 2003 and December 2004 2007 2001

  17. Recruiting patients from clinic: Attenders between January 2003 and December 2004 ? Died ? Remitted ? Lost hope 2007 2001

  18. What is the message? Recruiting current attenders is biassed towards: • Survivors • Continuing problems • Specific socio-economic groups • Treatment responders/non-responders • People who like you!

  19. Ideal • Whole population • Captured at time of onset (inception cohort)

  20. How to ascertain cases from whole population? Fix population: • Health plan coverage • Other special group (eg Nurses) • Geographical (beware of selection factors for 1 and 2)

  21. Tertiary Care Secondary Care Primary Care Self Care

  22. Threshold vary: • Disease severity • Socio-economic/education • Availability of care • Psychological factors

  23. Minimum entry severity point has to be primary care BUT Still legitimate to use other cut offs if external validity

  24. Choices for ascertainment • Detect diagnosed cases based on database search and chart review • Administrative database (eg Pharmex, GPRD) • Institutional database (eg Mayo Clinic) • Set up prospective system

  25. Use of diagnosed cases • Cheap • Quick • Will allow retrospective recruitment • Not relying on compliance

  26. Prospective system • Accuracy of data • Reliability of data • Timeliness of data • Build in appropriate follow up • ?consent/ethics

  27. Attrition:Losses from cohort Why: • Die • Get better • Deteriorate (DNA) • Lose interest • Change doctor • Move

  28. In practice: Losses from cohort are greater threat to validity that failure to recruit

  29. Minimise attrition • Engaging subjects with research • Frequent contact • Feedback • Consent • Baseline data on key informants • Consent to access medical and other records • Linkage to other datasets • Subjects do opt in

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