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Correlation of SF-12 and SF-36 in a Trauma Population1

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Background

The SF-36 is a commonly used general measure of health-related quality of life (QoL). The SF-12 is a related tool with less response burden, but its performance in a general trauma population is unknown. Hypothesis: The SF-12 would provide similar QoL information to the SF-36 in blunt trauma patients.

Methods

Adults with nonneurological blunt injury were prospectively enrolled. Demographic, injury, and socioeconomic data were collected. Patients were assessed with functional and psychologic questionnaires 1 and 6 months after injury. Physical (PCS) and mental (MCS) component scores of the SF-36 and SF-12 were compared using Pearson’s correlation coefficient. Linear regression identified factors associated with the SF-12 and SF-36 PCS and MCS. Responsiveness to change was assessed using the standardized response mean.

Results

Correlation of the PCS was 0.924 and MCS was 0.925 (both P < 0.001). QoL remained below population norms at 6 months. PCS was moderately responsive to change and was equivalent using either the SF-12 or the SF-36. MCS was not responsive to change using either tool. At both time points, at least 25% of patients with normal SF-12 PCS or MCS had SF-36 subscale scores significantly below the normal population.

Conclusions

The SF-12 can be used to assess QoL in trauma patients. The lack of responsiveness to change of the MCS suggests other methods may be necessary to fully evaluate mental QoL. Summary scores may not be sufficient to fully assess QoL in this population. Combining the SF-12 with measures to assess psychosocial variables should be further investigated.

Introduction

Traumatic injury is measured by the degree of physical and psychological impairment. Recovery can be assessed by return to normal functioning and estimation of the level of quality of life (QoL). Currently there are many instruments available to quantify the physical, functional, and psychological aspects of recovery from traumatic injury. One such instrument is the Short-form or SF-36 questionnaire. This is a widely used measure of health-related quality of life. It consists of 36 questions in eight subscales that assess physical, functional, social, and psychological well-being [1, 2]. The physical and mental component summary scales (PCS and MCS, respectively) are then calculated as composites of the related subscales. Scoring is standardized in the SF-36 using the means and standard deviations from the 1998 US general population. Studies have shown that, despite adequate physical functioning, trauma patients have significantly lower QoL than population norms [3, 4, 5].

The SF-12 contains a subset of 12 items taken from the SF-36. It includes at least one item from the eight health domains of SF-36, but it is shorter and has less response burden. While the SF-36 has been studied in the trauma population, the performance of the SF-12 in these patients is unknown. Therefore, the aim of this study was to compare QoL measured by the SF-36 and SF-12 at 1 and 6 months after traumatic injury. We hypothesized that the SF-12 would provide similar QoL information to the SF-36 in blunt trauma patients.

Section snippets

Study Population

Patients older than 18 years with blunt injury were prospectively identified during review of the daily trauma admission lists from Froedtert Memorial Lutheran Hospital. All patients older than 55 years and those 18-55 years with an Injury Severity Score (ISS) of ≥9 were included. An ISS of at least 9 was chosen to focus on those with moderate and severe injuries. Patients with head or spinal cord injuries were excluded. Eligible patients were enrolled after informed consent was obtained.

Patient Population

The demographic, clinical, and socioeconomic factors for survey responders are shown in Table 1. Three hundred twelve patients were enrolled in the study: 203 total patients responded to the surveys, for a response rate of 65%; 196 had 1-month and 123 had 6-month data available, for response rates of 62.8 and 39.4%.

Comparison of PCS and MCS Scores

Table 2 shows that PCS scores improved over time for both measures. Scores were also significantly lower than population norms at both 1 and 6 months. In addition, the change in the

Discussion

Prior to use of a new instrument to measure QoL, it must be validated. The SF-12 has been validated in general populations and in populations with chronic disease, but to our knowledge has not been previously published as an outcome tool in the trauma population. The trauma population differs from general populations in several ways: it is younger; more predominantly male; has a higher rate of PTSD, depression, poverty, and unemployment; and has a greater degree of functional limitation. The

Acknowledgments

The authors thank Kevin L. Weidner, MS, for assistance with data collection. Funding was provided by CDC Grant R49CCR519614.

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1

Presented at the 1st Annual Academic, Surgical Congress, San Diego, CA, February 8–11, 2006.

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