How can we know whether short term trends in a hospital's HSMR are significant?

The Hospital Standardized Mortality Ratio (HSMR) has been chosen by CIHI as its primary mortality measure. The indirect standardization used in the calculation of HSMR does not allow for valid comparison between hospitals but it does invite the assessment of quarterly trends in hospital mortality. However, statistical methods for assessing HSMR trends are not well-developed. In 2007 one large hospital in our health authority had four consecutive quarters of apparently increasing HSMR. As a result, we needed to assess the significance of this trend which, if it were to continue into the next quarter, would lead to an HSMR that significantly exceeded 100. We explored four methods to assess statistical significance of time trends in HSMR data: the WINPEPI "Describe" module, the CUSUM representation of Observed-Expected differences, the Variable Life Adjusted Display (VLAD) plots with CUSUM overlays, and the Change Point Analysis using Monte Carlo simulation.