Are survival rates for Tyrol published in the Eurocare studies biased?

OBJECTIVE

To investigate whether survival rates published in the EUROCARE studies for Tyrol are distorted, we evaluated data quality in the Cancer Registry of Tyrol.

MATERIAL AND METHODS

Potential errors in completeness of Tyrolean incidence data were assessed by applying semi-quantitative and quantitative methods, in part by comparing indices for Tyrol with those of neighboring countries published in Cancer Incidence in Five Continents. Validity of patient survival status was checked for all cancer patients diagnosed in 1997 (n2 556). For all 1 026 of these patients still alive at end of 2007, we reassessed survival status. Finally, we re-abstracted date of diagnosis for a subset of 295 patients.

RESULTS

Quality indices on completeness showed no greater bias with the exception of borderline ovarian cancer, which was in part miscoded in the early nineties. Some differences for bladder cancer and prostate cancer between Tyrol and neighboring countries are due to PSA testing and pathology diagnosis. Concerning patient survival status, four cases were erroneously assessed as alive, five cases died outside Austria, three cases were proven not to belong to the population of Tyrol at time of diagnosis and 21 cases emigrated. Absolute errors in survival rates were less than 0.5 for up to five-year survival rates and less than 1.0 for ten-year survival rates.

CONCLUSIONS

Evaluation of data quality in the Cancer Registry of Tyrol demonstrated that the survival rates published for Tyrol are only minimally biased by registration or analysis procedures. However, access to data on emigration,which until now is not possible because of data protection restrictions, would reduce the bias in patient survival status, bearing in mind that the extent of emigration of cancer patients is expected to increase in Austria over the coming years.