Using separation dates to define the relevant hospital admissions may have led to some bias in the results. At the time of diagnosis, using hospital admissions with separation days at or after the date of diagnosis should have captured all relevant activity at the beginning of the three-year time period. This was confirmed by the finding that there were no hospital admissions with separation dates before the diagnosis date with CRC diagnostic codes. However, it is possible that cases were in hospital on the third anniversary of the diagnosis date and thus would not be captured in the time period selected. This could result in a bias against cases that had prolonged hospital admissions in the latter part of the three-year study period.

The present study’s $1300 annual estimate of average population hospital costs was somewhat higher than the estimate made by Roos and Shapiro, who suggested an annual cost of $800 for 1988 to 1992 in Manitoba. They arrived at their estimate by dividing the total provincial hospital budget by the total population. Their total budget includes the cost for long term stay facilities and acute care hospitals, while the estimate in this study is based only on the acute care hospitals in which patients with CRC are admitted. The population costs estimated in this Nova Scotia study were also matched to the age-sex distribution of the CRC patients and thus would represent an older group than the entire Manitoba population. Spend less money now – for your efficient drug to cost less.

The data used to perform the cost calculations were not complete. The 40 cases without MSI numbers in the Nova Scotia Cancer Registry data were not likely typical of the rest of the cases. They were older and had a much shorter mean survival time than the whole group because 35 of these cases were identified only at the time of death.

The estimated costs for the severity groups showed a trend toward higher costs for the older, more complicated groups, which was expected. These severity groups are defined in an analogous fashion to the Canadian Institute of Health Information case mix groups (CMGs) (Table 1). The major difference is that the most responsible diagnosis in the CMG system is determined after the admission is complete, while the diagnoses in the ASD data were not necessarily defined in that manner from 1990 to 1994. Groupings were not assigned to cases during the time period studied in the Nova Scotia data sets. Severity groups B and C are similar in scope to that of CMG 256, and severity group D is similar to CMG 257. Jacobs et al found the cost for CMG 256 and CMG 257 to be $4,278 and $5,723 at the University of Alberta Hospital during 1992 to 1993, compared with the present study in which costs of $8,005 and $9,571, respectively, were estimated. Jacobs et al assigned costs prospectively using a patient resource consumption profile. Although the present study’s higher cost estimates may reflect a cruder costing method, they may also reflect a longer length of stay (19.3 days for severity groups B and C and 24.3 days for severity group D) than the University of Alberta Hospital, which had an average length of stay of 12.9 days for surgical cases. Jacobs et al studied patients who were admitted to ‘short stay’ home care programs after their acute care surgical admission. Such facilities were largely unavailable in Nova Scotia in 1990 to 1994 and may have allowed shorter lengths of stay for recovery after surgery. They found a per diem cost of $523 for surgical cases and $262 for medical cases. These were similar to the present study’s overall per diem cost of $390.