Volume 12, Number 5—May 2006
Dispatch
Costs of Surgical Site Infections That Appear after Hospital Discharge
Nicholas Graves*†
, Kate Halton*†, Merrilyn Curtis*, Shane Doidge*, David Lairson‡, Marylou McLaws§, and Michael Whitby*
, Kate Halton*†, Merrilyn Curtis*, Shane Doidge*, David Lairson‡, Marylou McLaws§, and Michael Whitby*Table A3
Description of Statistical Analyses
| All analyses were carried out using Stata software (Stata Statistical Software: Release 9.1, Stata Corp., College Station, TX, USA). |
| Evidence of multicollinearity was assessed by nested auxiliary regression, each variable was dropped from the model and the R-squared values compared to a complete model (i.e., the vif command in Stata was used to estimate variance inflation factors and the tolerances). |
| Nonnormality in dependent variables was assessed by visual inspection of data plots, and the Breusch-Pagan test was used as a formal test for heteroskedastic errors (i.e., the hettest command in Stata). |
| Terms that described interactions between socioeconomic and clinical variables were included, and the constrained model was compared with a number of unconstrained models; incremental F-tests were conducted (i.e., the test command in Stata was used). |
| Because the objective of the analyses was to estimate the independent effect of surgical site infections on cost outcomes, we included all available explanatory variables in a general model and did not seeks a general-to-simple reduction based on lack of statistical significance. |
