1. Validity of Diabetes
Prevalence from Health Data
Simon Thornley, Craig Wright, Roger Marshall,
Gary Jackson, Paul L Drury, Susan Wells, James
Smith, Wing Cheuk Chan, Romana Pylypchuk, Rod
Jackson.
NZSSD Conference
Apr 2010
Simon Thornley, Wing
Cheuk Chan, Paul Drury, Rod Jackson

2. Outline

Diabetes prevalence

Routine data

Accuracy

Compare to primary care
database

Capture-Recapture

Diagnosed vs undiagnosed

3. Diabetes Prevalence

Rapid increase last
30 years

Time trends

Health Planning

Primary Prevention
efficacy

4. Surveys

e.g. 2005 NZHS

Not frequent

Limited by selection
bias (e.g. 70%
response)
Simon Thornley, Wing
Cheuk Chan, Paul Drury, Rod Jackson

5. Health data
Linked by NHI
Dispensing, Diagnoses, Labs,
Mortality, GP.
Improved quality since 2006,
>90% NHI linkage
Similar overall prevalence to
survey results (Smith 2010)
Simon Thornley, Wing
Cheuk Chan, Paul Drury, Rod Jackson

6. Algorithm
 Record review
 Diabetes if:
 5+ HbA last two years
1c
 Hospital ICD(1998-2008)
 Diabetes clinic ('04-'08)
 Dispensing ('01-'08)
Simon Thornley, Wing
−insulin/oral hypo
Cheuk Chan, Paul Drury, Rod Jackson

7. Aim

Assess validity of
derived diabetes
prevalence

Compare to Primary
care cohort
(PREDICT) Wing
Simon Thornley,
Cheuk Chan, Paul Drury, Rod Jackson

8. “Gold Standard”
 PREDICT TM CVD RISK
 GP entered diagnosis.
 >100,000('00-'10)
 54,000 enter '07-'08
 Upper North Island
Simon Thornley, Wing
Cheuk Chan, Paul Drury, Rod Jackson

9. Agreement?

PREDICT vs.
Algorithm?

Sensitivity,
Specificity, Kappa

Capture-Recapture
Simon Thornley, Wing
Cheuk Chan, Paul Drury, Rod Jackson

10. 
Recording of diabetes status?
Simon Thornley, Wing
Cheuk Chan, Paul Drury, Rod Jackson

11. Results

PREDICT: 53,911

20% Pac, 16% Maori

Diabetes prevalence

20.1% Algorithm

20.9% PREDICT

23.7% Capture-recap
Simon Thornley, Wing
Cheuk Chan, Paul Drury, Rod Jackson

12. Results

Good agreement

Sens~86% P(A+|P+)

Spec~96% P(A-|P-)

Kappa~85%

Capture-Recapture

~15% undercount in Algorithm

~10% undercount in PREDICT
Simon Thornley, Wing
Cheuk Chan, Paul Drury, Rod Jackson

13. Agreement Diagram
Total
Algorithm
PREDICT Simon Thornley, Wing
Cheuk Chan, Paul Drury, Rod Jackson

14. Summary

Algorithm is
accurate

High level
agreement

Cheap, cost-
effective method
Simon Thornley, Wing
Cheuk Chan, Paul Drury, Rod Jackson

15. Thank You
Dr Simon Thornley, Lecturer,
University of Auckland
Section of Epidemiology and Biostatistics
s.thornley@auckland.ac.nz
www.slideshare.net/sithor
Simon Thornley, Wing
Cheuk Chan, Paul Drury, Rod Jackson