Article Text

Age related differences in work injuries and permanent impairment: a comparison of workers’ compensation claims among adolescents, young adults, and adults
1. C Breslin,
2. M Koehoorn,
3. P Smith,
4. M Manno
1. Institute for Work & Health, Toronto, Ontario
1. Correspondence to:  Dr C Breslin, Institute for Work & Health, 481 University Ave., Suite 800, Toronto, ON M5G 2E9, Canada;   cbreslin{at}iwh.on.ca

## Abstract

Background: There is growing evidence that adolescent workers are at greater risk for work injury.

Aims: To investigate the severity of work injuries across age groups.

Methods: Workers’ compensation records were used to examine work related injuries among adolescents (15–19 years old), young adults (20–24 years old), and adults (25+ years old) between 1993 and 2000. The incidence of compensated injuries was calculated for each age group and compared by gender, industry, and type of injury. The presence and degree of permanent impairment in each age group was also examined.

Results: For males, adolescents and young adults had higher claim rates than adults. For females, adults had the highest claim rates and young adults the lowest. Rates of permanent impairment indicated that age was positively associated with severity of injury.

Conclusions: Indicators of health consequences, in particular presence of permanent impairment, provide preliminary evidence that compensated work injuries sustained by youth are not as serious as injuries sustained by adults. Nevertheless, there was evidence that some young workers sustain injuries that have long term consequences. Documenting the consequences of the injuries that young workers sustain has implications for secondary prevention efforts and health services policy.

• lost time claims
• permanent impairment
• severity
• young workers
• ED, emergency department
• LT, lost time
• WMSD, work related musculoskeletal disorders

## Statistics from Altmetric.com

Even though young workers may be injured more frequently than their adult counterparts, it is not clear whether the severity of the injuries is similar across age groups. One indicator of the severity of the work injury is whether it resulted in permanent impairment. Fifteen to 26% of adolescent workers surveyed report permanent impairments, with the most common impairments being chronic pain, scarring, sensory loss, and loss of range of motion.12,13 The proportion of injured adolescent workers who are determined to have a permanent impairment varies markedly in workers’ compensation claim data, from a low of 3.4% of injured adolescent in Texas to 40% in New York state.6,8 Comparisons across compensation systems are difficult because of differences in definitions of permanent impairment, how it was assessed, and the level of compensation associated with permanent impairment. Nevertheless, these studies suggest that some adolescents do experience permanent impairment for work injuries. However, whether permanent impairment occurs as often among adolescent and young adult workers as adult workers remains to be determined.

Using workers’ compensation data, the primary goal of this study was to determine the incidence rates and severity of work related injuries among adolescents (15–19 years old), young adults (20–24 years old), and adults (25+ years old). Specifically we sought to examine the following research questions: (1) are gender differences in claim rates similar across different age groups; (2) are any age related differences in claim rates exhibited in both goods producing and service sectors; (3) are certain types of injuries more common among young workers than adult workers; and (4) is the presence and degree of permanent impairment comparable across age groups?

## METHODS

For the years 1993 to 2000, accepted, short term injury claims (that is, less than one year) involving wage replacement for time loss were obtained for workers 15 years and older from the workers’ compensation system in Ontario. In 1999, 68% of Ontario workers were covered through the compensation system.28 Workers not covered included those self employed, domestic workers, federal government workers, the majority of the finance industry, and workers associated with interprovincial commerce (for example, railroads).

In Canada, minimum age restrictions on work are primarily regulated by each province.29,30 In Ontario, for example, the regulations set 14 years old as the minimum age for employment in offices or stores, 15 for factory work, 16 for logging, and 18 for underground mining. Other Canadian jurisdictions such as British Columbia restrict paid employment for adolescents under 15, but only prohibit very hazardous jobs (for example, use of chemical toxins, explosives) between the ages of 15 and 17 years. Whether legally or illegally employed, workers under 18 years are entitled to wage replacement due to time loss if the injury occurred while working for a firm covered by the compensation system.

Each lost time (LT) claim included information on sociodemographics such as age and gender, industrial sector, the nature of the injury, and the presence and degree of permanent impairment. The industrial classification is based on the industry the claimant’s firm operates in and is coded according to the 1980 Standard Industrial Classification codes at the four digit level.31 This classification system can be aggregated into two major industrial groups, the goods producing (for example, manufacturing) and service sectors (for example, food service).

The Canadian Work Injury Standard codes were used to classify the nature of the injury.32 For this study, sprains and strains were categorised separately from other work related musculoskeletal disorders (WMSD; for example, tendinitis, inflammation of joints).

Workers who suffer permanent impairment due to workplace injuries are entitled to permanent impairment benefits under the Workers’ Compensation Act.33 Workers were eligible for these benefits if their impairment was unlikely to change substantially in the next year with or without treatment. The presence and degree of permanent impairment was determined by physicians and were based on formulae outlined in the Guides to the evaluation of permanent impairment, 4th edition.34 This evaluation system also provides specific guidelines for assessing the degree of impairment, ranging from 0% to 100% impairment. In the present study, presence of impairment was defined as 1% or more.

### Analytical strategy

Incidence rates per 1000 full time equivalents (FTEs) for lost time claims were computed by age group. Estimates of the number of workers and work hours for each age group (that is, denominators) were derived from the Canadian Labour Force Survey.35 People working in the finance and federal government industries were excluded as it is likely they are not covered under the mandate of the Workplace Safety and Insurance Board. For each month between 1993 and 2000, the total hours worked was estimated for Ontario workers. The FTE estimates were then summed across the years 1993 to 2000 to give an FTE estimate across the time period of this study by age group, stratified by gender and industry.

Confidence intervals for the incidence rates were used to assess age related differences (for formula used to calculate confidence intervals, see the appendix).

## RESULTS

Table 1 presents the claim rates by age and gender. These rates are based on work hours reported by each age/gender subgroup across the 1993–2000 time period. Across all age groups, the claim rate for males was approximately twice that for females. Among males, young adult males had the highest injury rates (43.2/1000 FTEs), followed by adolescent and adult males (39.3/1000 and 34.6/1000, respectively). Among females, adult females had the highest claim rate (20.96/1000 FTEs) and young adults the lowest (18.54/1000), with adolescent females falling in between (20.21/1000).

Table 1

Number and rate of lost time claims by gender and age group, 1993–2000

Table 2

Number and rate of lost time claims by industry and age group, 1993–2000

Table 3 shows claim rates by age, gender, and nature of injury. Within each age/gender group, sprains and strains represented the highest proportion of claims. However, the rate of sprains and strains for adolescents (males = 10.56/1000 FTEs; females = 5.85/1000) was significantly lower compared to adults (males = 15.75/1000 FTEs; females = 10.26/1000). Although young adult females (7.97/1000 FTEs) also showed a lower rate of sprains and strains than adult females, young adult males (16.10/1000) showed a slightly higher rate than adult males. Rates of cuts were significantly higher among adolescents (males = 8.77/1000 FTEs; females = 3.61/1000) and young adults (males = 6.50/1000 FTEs; females = 1.77/1000) than adults (males = 3.00/1000 FTEs; females = 1.09/1000).

Table 3

Number and rate of lost time claims by nature of injury and age group, 1993–2000

Table 4 shows the rate of permanent impariments by age group. Overall, adolescents (0.59/1000 FTEs) had a lower rate of permanent impairment compared to young adults (1.02/1000) and adults (2.54/1000). This age related trend held for all but three types of injuries (amputations, burns, and cuts). Most notably, adolescents (0.17/1000 FTEs) showed a significantly higher rate of permanent impairment for amputations than adults (0.11/1000). To better understand why all amputations were not assessed as resulting in permanent impairment, we broke down the claims for amputations by part of the body. Across all age groups, 95% of amputations involved the finger or finger tip. Thus, some of these types of amputations appeared to have been judged to not have impaired functioning.

Table 4

Number and rate of lost time claims with permanent impairment by type and age group, 1993–2000

Within each age group, the type of injury with the highest rate of permanent impairment differed. For adolescents, amputations had the highest rate of permanent impairment (0.17/1000 FTEs), while sprains and strains led to the highest rate of permanent impairment for the other age groups (young adults, 0.27/1000; adults, 1.03/1000).

Among those with permanent impairment, we also calculated the mean percentage impairment rating by age group, another indicator of the level of injury severity. Adolescents showed the lowest impairment rating (mean = 11.64, CI 95% 10.71 to 12.58), and this mean rating was not significantly different from the mean rating for young adults (mean = 12.91, CI 95% 12.53 to 13.29). However, adults had a significantly higher mean impairment rating (mean = 15.48, CI 95% 15.38 to 15.57) than adolescents or young adults.

## DISCUSSION

As with previous studies, variation in claim rates by industry and by type of injury suggest that work related risk factors such as hazard exposure contribute to young worker’s increased risk. However, the notion that cognitive and physical development play a major role in injury risk is not strongly supported by our findings. In particular, young adult males had the highest injury rate, an age group where maturational factors would be less plausible for explaining injuries. Even though maturational factors may be relevant, these findings for males may indicate that a different combination of general risk factors (for example, work hazards) and unique risk factors (for example, stage of maturation) may operate across adolescence and young adulthood.

Across age groups, musculoskeletal conditions (that is, strains and sprains) were an important part of the work injury picture in this study. Sprains and strains were the leading cause of injury for all age groups, though they constituted a smaller proportion of adolescent claims. Nevertheless, musculoskeletal disorders, especially back injuries, may increase young workers’ vulnerability to further injuries. Evidence from several studies indicates that a history of back problems is a predictor of future back injuries and delayed recovery.36–40 Musculoskeletal conditions also appeared to be the primary contributor to the progressive increase across age groups in rates of permanent impairment. Indeed, the adult rate of permanent impairment for sprains and strains alone was higher than the adolescent rates of permanent impairment for all types of injuries combined. These marked differences with respect to chronic conditions such as musculoskeletal disorders might be partially explained by the fact that adolescents have not only had less time for musculoskeletal disorders to arise, but also have had less time to show a history of impaired work functioning due to such a condition, an essential part of the assessment to determine permanent impairment. Given the age related pattern we have observed in this study, it appears that programmes designed to prevent or minimise the impact of musculoskeletal disorders should be implemented in adolescence or young adulthood, before these conditions become the prominent part of the adult lost time claim and permanent impairment picture.

Certain limitations associated with this administrative data should be noted. Workers who are self employed or who work in small family businesses may not be well represented in the lost time claim figures. Even in work settings covered by workers’ compensation, underreporting of work injuries is one issue that may be particularly relevant to youth.13 Consequently, the conclusions based on these data should be viewed as tentative, but justified in light of the limited number of previous studies examining age related differences in work injuries and their long term consequences.

The present findings provide preliminary support for policy recommendations regarding primary and secondary prevention. Given the limitations of workers’ compensation data, relevant federal and provincial agencies should develop a comprehensive plan for monitoring work related injuries and for monitoring biochemical, physical, and psychosocial hazards to which workers are exposed. In particular, additional resources could be allocated to monitor injuries of individuals just starting a job or entering the labour force. Effective and comprehensive health and safety training for adolescents and young adults has rarely been evaluated (for an exception, see Banco and colleagues41). Consequently, federal and provincial ministries of labour and education should determine the effectiveness and coverage of current school based and work based safety training initiatives. In terms of secondary prevention, health care services could be targeted to reduce the duration and severity of the disability associated with a work injury. Permanent impairment among adolescents and young adults, though less frequent than for adults, is of concern because these long term health consequences may result in increased need of health care services into adulthood. In addition people with permanent disabilities show reduced earning capacity and increased risk of poverty.42 Medical and behavioural intervention provided early in the disability process may enhance the functional capacity of the injured worker.

## APPENDIX: ESTIMATION OF RATE PARAMETER AND CORRESPONDING VARIANCE

Assume we observe iid count data x1, x2, ..., xn with corresponding follow up or exposure times t1, t2, ..., tn. We assume each count comes from a Poisson distribution with frequency function:

$Math$

Hence, each count has mean and variance λti.

We are interested in estimating the rate parameter λ and its corresponding variance. The likelihood is given by:

$Math$

Taking logarithms and disregarding terms that don’t involve λ, we get:

$Math$

Differentiating with respect to λ gives:

$Math$

Setting the expression to zero and solving for λ gives the following estimator:

$Math$

An estimate for the variance can be obtained using the relation:

$Math$

where the expectation is taken with respect to the xi’s. Application of the above formula gives:

$Math$

Since we don’t know the value of λ, so we replace it in the above expression with its estimate λ. A 95% confidence interval for λ can then be constructed based on the above estimate and variance formula, i.e.

$Math$

However, because the sampling distribution of λ tends to be skewed and non-normal, this formula is not the best choice for constructing a confidence interval. Another undesirable property of the above formula is the potential to get a lower confidence bound which is negative. An improved confidence interval can be obtained by considering the log transformation of λ. An application of the delta method (see Agresti43 for example) yields, after some simplification, the following variance estimate for log λ:

$Math$

A 95% confidence interval for λ is then given by:

$Math$

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