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Use of Whole Population Registers: Advantages and Disadvantages.

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Presentation on theme: "Use of Whole Population Registers: Advantages and Disadvantages."— Presentation transcript:

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 Your area Your Clinic Other clinics

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

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

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

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

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

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

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: 1.Health plan coverage 2.Other special group (eg Nurses) 3.Geographical (beware of selection factors for 1 and 2)

21 Self Care Primary Care Secondary Care Tertiary 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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