Methodological issues in international comparison of interval XXXX .

@entity5 @entity0
International comparisons of @entity5 ( @entity5 ) are important to better understand the relationship between programmes' performance and screening practices. In this respect, differences in (i) definition, (ii) identification and (iii) quantification of @entity5 have received little attention. To examine these 3 comparability issues and activities involving @entity5 , an assessment was conducted among member countries of the International Breast Cancer Screening Network, and the impact of accuracy of identification and quantification practices was estimated using 1996-98 data from the Dutch @entity0 screening programme. Information was obtained from 19 screening programmes in 18 countries, 16 of which acknowledged the coexistence of opportunistic screening. @entity5 data were collected to evaluate performance of the screening programme (100% of programmes) and the radiologists (89%); 53% of programmes had a designated review process for @entity5 . Most programmes (84%) agreed with the European Guidelines definition of @entity5 , but a case situation exercise evidenced substantial discrepancy in classification of @entity5 that occurred after a positive screen. Completeness of identification of @entity5 appears to contribute most to international variation, and cannot be easily controlled for in methodologically rigorous comparisons. Statistically significant differences of about 4% were measured between quantification methods for @entity5 . An operational definition of @entity5 is proposed to enhance international comparability. Valid comparisons of @entity5 are possible with careful attention to the definition but true differences in @entity5 frequency across screening programmes should exceed 10% to be possibly indicative of real differences between programmes.
