The Swedish two-county trial of mammographic screening: Cluster randomisation and end point evaluation

Stephen W. Duffy, L. Tabar, B. Vitak, M. F. Yen, J. Warwick, R. A. Smith, H. H. Chen

Research output: Contribution to journalArticle

48 Citations (Scopus)

Abstract

Background: The Swedish Two-County Trial has been criticised on the grounds of the cluster randomisation and alleged bias in classification of cause of death. Patients and methods: In the Two-County Trial, 77080 women were randomised to regular invitation to screening (active study population, ASP) and 55985 to no invitation (passive study population, PSP), in 45 geographical clusters. After ∼7 years, the PSP was invited to screening and the trial closed. We analysed data using hierarchical statistical models to take account of cluster randomisation, and performed a conservative analysis assuming a systematic difference between ASP and PSP in baseline breast cancer mortality in one of the counties. We also analysed deaths from causes other than breast cancer and from all causes among breast cancer cases diagnosed in the ASP and PSP. Results: Taking account of the cluster randomisation there was a significant 30% reduction in breast cancer mortality in the ASP. Conservatively, assuming a systematic difference between ASP and PSP clusters in baseline breast cancer mortality, there was a significant 27% reduction in mortality in the ASP. Ignoring classification of cause of death, there was a significant 13% reduction in all-cause mortality in breast cancer cases in the ASP. Conclusions: Breast cancer mortality is a valid end point and mammographic screening does indeed reduce mortality from breast cancer. The criticisms of the Swedish Two-County Trial are unfounded.

Original languageEnglish
Pages (from-to)1196-1198
Number of pages3
JournalAnnals of Oncology
Volume14
Issue number8
DOIs
Publication statusPublished - Aug 1 2003
Externally publishedYes

Fingerprint

Random Allocation
Breast Neoplasms
Population
Mortality
Cause of Death
Statistical Models

Keywords

  • Breast screening
  • Mammography
  • Randomised trial

ASJC Scopus subject areas

  • Oncology
  • Cancer Research

Cite this

The Swedish two-county trial of mammographic screening : Cluster randomisation and end point evaluation. / Duffy, Stephen W.; Tabar, L.; Vitak, B.; Yen, M. F.; Warwick, J.; Smith, R. A.; Chen, H. H.

In: Annals of Oncology, Vol. 14, No. 8, 01.08.2003, p. 1196-1198.

Research output: Contribution to journalArticle

Duffy, Stephen W. ; Tabar, L. ; Vitak, B. ; Yen, M. F. ; Warwick, J. ; Smith, R. A. ; Chen, H. H. / The Swedish two-county trial of mammographic screening : Cluster randomisation and end point evaluation. In: Annals of Oncology. 2003 ; Vol. 14, No. 8. pp. 1196-1198.
@article{3f67a8b929ed45c78d35d775a2253f24,
title = "The Swedish two-county trial of mammographic screening: Cluster randomisation and end point evaluation",
abstract = "Background: The Swedish Two-County Trial has been criticised on the grounds of the cluster randomisation and alleged bias in classification of cause of death. Patients and methods: In the Two-County Trial, 77080 women were randomised to regular invitation to screening (active study population, ASP) and 55985 to no invitation (passive study population, PSP), in 45 geographical clusters. After ∼7 years, the PSP was invited to screening and the trial closed. We analysed data using hierarchical statistical models to take account of cluster randomisation, and performed a conservative analysis assuming a systematic difference between ASP and PSP in baseline breast cancer mortality in one of the counties. We also analysed deaths from causes other than breast cancer and from all causes among breast cancer cases diagnosed in the ASP and PSP. Results: Taking account of the cluster randomisation there was a significant 30{\%} reduction in breast cancer mortality in the ASP. Conservatively, assuming a systematic difference between ASP and PSP clusters in baseline breast cancer mortality, there was a significant 27{\%} reduction in mortality in the ASP. Ignoring classification of cause of death, there was a significant 13{\%} reduction in all-cause mortality in breast cancer cases in the ASP. Conclusions: Breast cancer mortality is a valid end point and mammographic screening does indeed reduce mortality from breast cancer. The criticisms of the Swedish Two-County Trial are unfounded.",
keywords = "Breast screening, Mammography, Randomised trial",
author = "Duffy, {Stephen W.} and L. Tabar and B. Vitak and Yen, {M. F.} and J. Warwick and Smith, {R. A.} and Chen, {H. H.}",
year = "2003",
month = "8",
day = "1",
doi = "10.1093/annonc/mdg322",
language = "English",
volume = "14",
pages = "1196--1198",
journal = "Annals of Oncology",
issn = "0923-7534",
publisher = "Oxford University Press",
number = "8",

}

TY - JOUR

T1 - The Swedish two-county trial of mammographic screening

T2 - Cluster randomisation and end point evaluation

AU - Duffy, Stephen W.

AU - Tabar, L.

AU - Vitak, B.

AU - Yen, M. F.

AU - Warwick, J.

AU - Smith, R. A.

AU - Chen, H. H.

PY - 2003/8/1

Y1 - 2003/8/1

N2 - Background: The Swedish Two-County Trial has been criticised on the grounds of the cluster randomisation and alleged bias in classification of cause of death. Patients and methods: In the Two-County Trial, 77080 women were randomised to regular invitation to screening (active study population, ASP) and 55985 to no invitation (passive study population, PSP), in 45 geographical clusters. After ∼7 years, the PSP was invited to screening and the trial closed. We analysed data using hierarchical statistical models to take account of cluster randomisation, and performed a conservative analysis assuming a systematic difference between ASP and PSP in baseline breast cancer mortality in one of the counties. We also analysed deaths from causes other than breast cancer and from all causes among breast cancer cases diagnosed in the ASP and PSP. Results: Taking account of the cluster randomisation there was a significant 30% reduction in breast cancer mortality in the ASP. Conservatively, assuming a systematic difference between ASP and PSP clusters in baseline breast cancer mortality, there was a significant 27% reduction in mortality in the ASP. Ignoring classification of cause of death, there was a significant 13% reduction in all-cause mortality in breast cancer cases in the ASP. Conclusions: Breast cancer mortality is a valid end point and mammographic screening does indeed reduce mortality from breast cancer. The criticisms of the Swedish Two-County Trial are unfounded.

AB - Background: The Swedish Two-County Trial has been criticised on the grounds of the cluster randomisation and alleged bias in classification of cause of death. Patients and methods: In the Two-County Trial, 77080 women were randomised to regular invitation to screening (active study population, ASP) and 55985 to no invitation (passive study population, PSP), in 45 geographical clusters. After ∼7 years, the PSP was invited to screening and the trial closed. We analysed data using hierarchical statistical models to take account of cluster randomisation, and performed a conservative analysis assuming a systematic difference between ASP and PSP in baseline breast cancer mortality in one of the counties. We also analysed deaths from causes other than breast cancer and from all causes among breast cancer cases diagnosed in the ASP and PSP. Results: Taking account of the cluster randomisation there was a significant 30% reduction in breast cancer mortality in the ASP. Conservatively, assuming a systematic difference between ASP and PSP clusters in baseline breast cancer mortality, there was a significant 27% reduction in mortality in the ASP. Ignoring classification of cause of death, there was a significant 13% reduction in all-cause mortality in breast cancer cases in the ASP. Conclusions: Breast cancer mortality is a valid end point and mammographic screening does indeed reduce mortality from breast cancer. The criticisms of the Swedish Two-County Trial are unfounded.

KW - Breast screening

KW - Mammography

KW - Randomised trial

UR - http://www.scopus.com/inward/record.url?scp=0042384967&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0042384967&partnerID=8YFLogxK

U2 - 10.1093/annonc/mdg322

DO - 10.1093/annonc/mdg322

M3 - Article

C2 - 12881376

AN - SCOPUS:0042384967

VL - 14

SP - 1196

EP - 1198

JO - Annals of Oncology

JF - Annals of Oncology

SN - 0923-7534

IS - 8

ER -