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