Use of Whole Population Registers: Advantages and Disadvantages.

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Use of Whole Population Registers: Advantages and Disadvantages

Transcript of Use of Whole Population Registers: Advantages and Disadvantages.

Page 1: Use of Whole Population Registers: Advantages and Disadvantages.

Use of Whole Population Registers:

Advantages and Disadvantages

Page 2: 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?

• Source of control group(s)?

Page 3: Use of Whole Population Registers: Advantages and Disadvantages.

Threats

• Internal validity

• External validity

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Problem with:‘my clinical series’

• Who are your patients?

• Which patients could you have included?

• Which patients have you lost– And why?

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Issue of Catchment population

Your area

Your Clinic

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Issue of Catchment population

Your area

Your Clinic

Other clinics

Page 7: Use of Whole Population Registers: Advantages and Disadvantages.

Issue of Catchment population

Your area

Your Clinic

Other Clinic

Page 8: Use of Whole Population Registers: Advantages and Disadvantages.

Issue of Catchment population

Your area

Your Clinic

Other Clinic ???

Page 9: Use of Whole Population Registers: Advantages and Disadvantages.

Issue of Catchment population

Your area

Your Clinic

Other Clinic???

Page 10: Use of Whole Population Registers: Advantages and Disadvantages.

Does it matter

• May or may not?

• Selection factors related to:– Disease severity– Access– Costs– Education– Co-morbidity– Waiting time etc

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Who gets lost:The issue of left censorship

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2001 2007

Recruiting patients from clinic

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2001 2007

Recruiting patients from clinic:

Attenders between January 2003 and December 2004

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2001 2007

Recruiting patients from clinic:

Attenders between January 2003 and December 2004

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2001 2007

Recruiting patients from clinic:

Attenders between January 2003 and December 2004

Page 16: Use of Whole Population Registers: Advantages and Disadvantages.

2001 2007

Recruiting patients from clinic:

Attenders between January 2003 and December 2004

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2001 2007

Recruiting patients from clinic:

Attenders between January 2003 and December 2004

? Died

? Remitted

? Lost hope

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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!

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Ideal

• Whole population

• Captured at time of onset (inception cohort)

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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)

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Self Care

Primary Care

Secondary

Care

Tertiary Care

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Threshold vary:

• Disease severity

• Socio-economic/education

• Availability of care

• Psychological factors

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Minimum entry severity point has to be

primary care

BUT

Still legitimate to use other cut offs if external validity

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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

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Use of diagnosed cases

• Cheap

• Quick

• Will allow retrospective recruitment

• Not relying on compliance

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Prospective system

• Accuracy of data

• Reliability of data

• Timeliness of data

• Build in appropriate follow up

• ?consent/ethics

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Attrition:Losses from cohort

Why:

• Die

• Get better

• Deteriorate (DNA)

• Lose interest

• Change doctor

• Move

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In practice:

Losses from cohort are greater threat to

validity that failure to recruit

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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