Errors in survival rates caused by routinely used deterministic record linkage methods

It was the objective of this study to assess the impact of applying various record linkage methods to one of the most important outcome measures in oncological epidemiology, namely survival rates.

To assess the life status of patients, incidence data published by the Cancer Registry of Tyrol were analyzed with three routinely used methods of record linkage for incidence and mortality data. Of these methods, two were deterministic and the third a probabilistic method developed by the Cancer Registry of Tyrol. We studied the impact of record linkage methods on a simple measure (mortality rate) and a more complex measure (relative survival rate). The analysis was based on the published incidence data for Tyrol for the years 1992 to 1996. Results of deterministic record linkage methods were simulated.

The error rates for simple mortality rate and relative survival rate are considerable. For the first deterministic record linkage method, relative differences in mortality rate range from 11.9% to 14.8% (men) and 24.5% to 28.2% (women) and relative differences in relative five-year survival from 11.4% to 16.3% (men) and from 19.3% to 26.4% (women). For the second deterministic record linkage method, relative differences in mortality rate range from 4.8% to 5.9% (men) and from 4.9% to 7.4% (women), while relative differences in relative five-year survival range from 5.1% to 7.0% (men) and from 4.4% to 6.1% (women).

Our study shows that in order to calculate valid mortality and survival rates a probabilistic method of record linkage must be applied.