Severity of illness-geriatric (SOI-G) : instrument development

Abstract

Controlling for the wide variability in the physical health status of geriatric populations is important as severity of illness is known to both moderate and suppress relationships examined in psychosocial research. The purpose of the present investigation was to develop a uniform, easily administered quantitative index of illness severity, composed of disease-specific scales, that was independent of psychosocial factors and appropriate for use with a geriatric population. As well, the aim was to collect preliminary data on the reliability and validity of the scale. The development of the Severity of Illness-Geriatric (SOI­G) scale involved the adaptation of a previously developed severity of illness instrument Severity of Renal Disease Scale (SORDS). The present investigation involved five programmatically linked studies. Study 1 involved the determination of the items to be included on SOI-G while Study 2 defined the severity criteria for each item. In Study 3, five geriatric specialists scaled each level of each item on the same underlying threat to life scale. There was a high level of initial agreement between the raters supporting the reliability of the severity values. The final scale consisted of 32 items. In Study 4, archival data was collected on 61 patients admitted to the geriatric unit of a rehabilitation hospital. The SOI-G was compared to the Cumulative Illness Rating Scale-Geriatric (CIRS-G) and a global severity rating. SOI-G inter-rater reliability estimates were low (likely due to rater error) but promising. SOI-G demonstrated support for content validity, face validity, and construct validity but evidence for convergent validity was not established. SOI-G scores were sensitive to differences among patients with respect to discharge outcome. The utility of SOI-G as a moderator variable in psychosocial research with the elderly could not be explored in Study 5 due to a limited sample size. It was concluded that the present investigation demonstrated the potential usefulness of SOI-G in psychosocial research with the elderly but further research is needed before definitive conclusions can be made. The SOI-G offers researchers a tool for controlling disease variability that is not measured by psychological tests but must be accounted for in research designs.