# Gainful employment and risk of mortality after spinal cord injury: effects beyond that of demographic, injury and socioeconomic factors

## Abstract

### Objective:

To evaluate the association of three levels of gainful employment with the risk of mortality after traumatic spinal cord injury (SCI) while controlling for known predictors of mortality status (including education and income).

### Study design:

Prospective cohort study

### Setting:

A total of 20 federally funded SCI Model Systems of care in the United States.

### Methods:

Participants included 7955 adults with traumatic SCI. Preliminary assessments were conducted between 1995 and 2006. Mortality status was determined by the Social Security Death Index (1308 deaths). A two-stage logistic regression model was used to estimate the chance of dying in any given year. Life expectancy was calculated under different economic assumptions.

### Results:

Compared with those who were working 30+ h per week, the odds of mortality was 1.37 for those who worked 1–29 h and 1.67 for those who were unemployed. The addition of gainful employment only modestly reduced the effects of household income and education, both of which remained significant. For instance, the odds of mortality for household income (referent $75 000+) decreased from 1.50 to 1.38 for$25 000–$75 000 and from 2.10 to 1.82 for <$25 000. Life expectancy varied widely depending on socioeconomic characteristics more than doubling under certain assumptions.

### Conclusion:

Substantial variation in mortality is attributable to employment, above and beyond the effects of previously established demographic, injury and socioeconomic predictors. Although some excess mortality may be the inevitable consequence of SCI, risk is substantially increased with poor socioeconomic characteristics.

## Introduction

Spinal cord injury (SCI) is related to an elevated risk of mortality, the extent of which depends on the location of the lesion and neurological completeness of injury.1 Because mortality rates among first-year survivors have remained essentially unchanged since the 1980s,1, 2 excess mortality is typically viewed as an inevitable consequence of SCI. However, research on factors other than demographics suggests that socioeconomic conditions may have a profound effect on risk of mortality, both in the general population and after SCI.3, 4, 5 This research has typically focused on education and income to the exclusion of gainful employment as a risk factor for mortality.

Three previous analyses of data from the SCI Model Systems (SCIMSs) in the United States indicated significant relationships between socioeconomic indicators and risk of mortality after SCI.6, 7, 8 In the first study, economic status was measured using the economic self-sufficiency score of the Craig Handicap Assessment and Reporting Technique, which has a relatively low ceiling of 1.5 times the poverty level, along with the type of insurance and several other predictors including health status.6 Both the economic self-sufficiency score and insurance were significantly related to both the probability of mortality and life expectancy. This study was replicated with smaller observed effects, largely due to a nonsignificant relationship between type of insurance and mortality.7 More recently, the effects of education and household income were isolated while controlling for demographic and injury characteristics.8 Compared with those with household income in excess of $75 000, those with annual household income of <$25 000 had a 2.31 greater odds of mortality, and those whose income was between $25 000 and$74 999 had a 1.61 greater odds of mortality. These findings were similar to those in an independent study using a smaller participant sample.9

These studies demonstrated the importance of income and education but did not address gainful employment. Studies in the general population have rarely addressed employment,3, 4, 5 as employment is fundamental to adult life and employment rates are typically high. However, given the low employment rates and the relationship of poor employment outcomes with policy factors (particularly work disincentives in the USA), employment may be a critical, yet overlooked, risk factor for mortality. A relationship between employment and mortality would suggest that risk of mortality may be decreased by policy or programmatic changes improving employment outcomes.

### Purpose

Our purpose was to identify the association of three indicators of socioeconomic status (SES) with risk of mortality and differential life expectancy using data from the SCIMSs in the United States. The unique contribution of this study was the demonstration of the relationship of three levels of employment (unemployed, 1–29 h and 30 h per week) with the risk of mortality while systematically building upon more limited analysis of established SES indicators (education and income). Therefore, we were able to isolate the relationship of employment with the risk of mortality above and beyond the effects of other aspects of SES to help determine the extent to which excess mortality is indeed an inevitable consequence of SCI.

### Hypotheses

1. 1

Employment status is significantly predictive of mortality after controlling for known risk factors.

2. 2

There is a decreasing risk of mortality as a function of the three levels of employment, with the lowest risk among those working the greatest number of hours.

3. 3

Education and household income will also be significantly related to risk of mortality.

## Materials and methods

### Participants

After obtaining the approval of the institutional review board, participants were recruited during acute care or inpatient rehabilitation at 1 out of 20 SCIMS hospitals. Eligibility criteria included: traumatic SCI, admission within 1 year of injury, discharged alive with some residual neurological deficit, minimum of 18 years of age, non-ventilator-dependent and having data on household income and employment collected at least once post discharge. The sample was comprised of 7955 participants from the previously reported study by Krause et al.8 (72 persons missing work hours were excluded).

### Procedures

The National Spinal Cord Injury Statistical Center contains data reported from SCIMS rehabilitation hospitals. Data were collected during inpatient rehabilitation and at discharge, 1 year post injury, 5 years post injury and at 5-year intervals thereafter through an in-person, telephone or mailed interview. All-cause mortality was assessed annually using the Social Security Death Index, an on-line mortality database, with the most recent searches conducted in February and March 2011. The Security Death Index has 94.2% sensitivity and 99.5% specificity in identifying mortality among persons in the National Spinal Cord Injury Statistical Center database.10 Participants who were not found deceased were presumed to be alive and their censoring date was either the most recent date of contact or 1 January 2011.

### Measures

Form I data are collected during inpatient rehabilitation, and Form II is data collected at follow-up. Several demographic and injury characteristics were taken from the Form I. Injury level was categorized as cervical 1–4 (C1–C4), cervical 5–8 (C5–C8) and non-cervical, whereas injury completeness was measured by either Frankel grade (the Frankel system was used until 1993)11 or the American Spinal Injury Association Impairment Scale (AIS).12 Each Frankel grade was grouped with the corresponding AIS grade. Other variables were sex, race, current age, calendar year and years since injury. Cause of injury was grouped as: (a) violent, (b) motor vehicle crash/fall/sports/unknown etiology and (c) other.8

### Future research

We need to identify the mechanisms by which SES is related to mortality, including access to health care, resources and psychological and biological measures that may covary with SES. Identification of systematic biases in the Security Death Index would help evaluate the quality of mortality analyses. More sophisticated policy studies are needed to more directly determine the effects of financial disincentives to employment on mortality rates. Lastly, we need to evaluate the extent to which socioeconomic factors are differentially related to causes of death.

## Conclusion

Gainful employment is inversely related with risk of mortality, above and beyond the effects of factors demonstrated in previous research including demographic, injury-related and other socioeconomic factors (education and income). These findings challenge the notion that current levels of mortality are the inevitable consequence of SCI.

## Data archiving

There were no data to deposit.

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## Acknowledgements

The contents of this publication were developed under grants from the Department of Education, NIDRR grant numbers H133N060009 and H133B090005. However, those contents do not necessarily represent the policy of the Department of Education, and you should not assume endorsement by the Federal Government. We would like to thank the following persons who contributed to the work reported in the manuscript: Richard Aust, Josh Acuna, Dr Yue Cao, Jennifer Coker, Emily Johnson and Karla Reed.

## Author information

Correspondence to J S Krause.

## Ethics declarations

### Competing interests

The authors declare no conflict of interest.

## Rights and permissions

Reprints and Permissions

Krause, J., Saunders, L. & Acuna, J. Gainful employment and risk of mortality after spinal cord injury: effects beyond that of demographic, injury and socioeconomic factors. Spinal Cord 50, 784–788 (2012) doi:10.1038/sc.2012.49

• #### DOI

https://doi.org/10.1038/sc.2012.49

### Keywords

• spinal cord injury
• mortality
• employment
• economics
• income
• life expectancy

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