ORIGINAL ARTICLES

Factors associated with duration of disability benefits: a cohort study

Factores asociados a la duración de los beneficios por incapacidad: un estudio de cohorte

Norma Suely Souto SouzaI, II; Vilma Sousa SantanaIII

IPrograma de Pós-Graduação em Saúde Coletiva. Instituto de Saúde Coletiva. Universidade Federal da Bahia (UFBA). Salvador, BA, Brasil
IIAuditoria Regional em Salvador. Instituto Nacional do Seguro Social. Salvador, BA, Brasil
IIIInstituto de Saúde Coletiva. UFBA. Salvador, BA, Brasil

Correspondence

ABSTRACT

OBJECTIVE: To analyze factors associated with the duration of disability benefits due to work-related upper-limb musculoskeletal disorders.
METHODS: Ambispective cohort study conducted with 563 insured workers from the General Social Security System who received temporary disability benefits due to work-related upper-limb musculoskeletal disorders in the city of Salvador, Northeastern Brazil, in 2008. The data came from an inquiry performed by the Regional Audit of the National Social Security Institute and from administrative records. Sociodemographic and work-related variables were analyzed, as well as characteristics of the health problem and aspects related to social security. Factors associated with time until the cessation of the benefit were identified through survival analysis techniques.
RESULTS: Low socioeconomic position (RR=1.29; 95%CI 1.02; 1.64), age below 39 years (RR=1.23;95%CI 1.03; 1.47), income replacement by the National Social Security Institute < 100% (RR=1.24; 95%CI 1.04; 1.47) and high expectation of returning to work (RR=1.20; 95%CI 1.00; 1.44) are the categories related to higher rate of cessation of the benefit and with its shorter duration.
CONCLUSIONS: Factors that are not strictly medical, like socioeconomic position, age, expectation of returning to work and level of income replacement by the National Social Security Institute, seem to influence the benefit's duration. These hypotheses need to be tested with further confirmatory studies in order to improve the understanding of the process of determining incapacity for work.

Descriptors: Sick Leave. Musculoskeletal Diseases. Insurance, Disability, utilization. Insurance Benefits. Insurance, Health. Occupational Health. Cohort Studies.

RESUMEN

OBJETIVO: Analizar factores asociados a la duración de los beneficios por incapacidad por enfermedades musculoesqueléticas en la región cervical y/o en miembros superiores relacionadas al trabajo.
MÉTODOS: Estudio de cohorte ambispectivo con 563 trabajadores asegurados del Régimen General de la Previdencia Social que recibieron beneficio por incapacidad temporal por enfermedades musculoesqueléticas de la región cervical y miembros superiores relacionadas con el trabajo en Salvador, Northeastern Brazil, en 2008. Los datos resultaron de una pesquisa conducida por la Auditoria Regional del Instituto Nacional del Seguro Social y de registros administrativos. Se analizaron variables sociodemográficas, relacionadas con el trabajo, características del agravio, y aspectos relacionados con el seguro social. Los factores asociados al tiempo hasta la cesantía del beneficio fueron identificados con técnicas de análisis de sobrevivencia.
RESULTADOS: Posición socioeconómica baja (RR= 1,29; IC95% 1,02;1,64), edad por debajo de 39 años (RR= 1,23; IC95% 1,03;1,47), reposición de renta por el Instituto Nacional del Seguro Social <100% (RR= 1,24; IC95% 1,04;1,47) y expectativa alta de retorno al trabajo (RR=1,20; IC95% 1,00;1,44) son las categorías relacionadas con mayor tasa de cesantía del beneficio y su menor duración.
CONCLUSIONES: Factores no estrictamente médicos, como posición socioeconómica, edad, expectativa relativa al retorno al trabajo y nivel de reposición de renta por el Instituto Nacional del Seguro Social parecen influenciar la duración del beneficio. Estas hipótesis deben ser evaluadas posteriormente con estudios confirmatorios para perfeccionar el entendimiento del proceso de determinación de la incapacidad para el trabajo.

Descriptores: Ausencia por Enfermedad. Enfermedades Musculoesqueléticas. Seguro por Discapacidad, utilización. Beneficios del Seguro. Seguro de Salud. Salud Laboral. Estudios de Cohortes.

INTRODUCTION

Incapacity for work caused by health-related injuries is a problem all over the world, with considerable social and economic cost. Approximately 3% to 10% of the economically active population in developed countries received benefits due to disability caused by health problems in 2003.14 The grant of these benefits has been vigorously increasing in Brazil, remarkably for temporary disability, which grew 138% (from 909,476 to 2,163,063) between 2000 and 2008.ª

Studies use measures of the duration of benefits receipt as indicators of the burden of disability in the population. The results show low correlation between physical limitation and duration of benefits receipt, mainly concerning chronic diseases. Factors beyond the specific to trigger or sustain health problems may explain differences in return to work or in the benefit's duration.5,10,17

Literature reviews have shown distinct predictors of the duration of incapacity for work, like individual characteristics of the worker, of the disease, of the health system, of social security, of work's demands, besides other factors such as discrimination, legal framework and unionization, which may influence the duration of the disability and the odds of returning to work.7,8,17 The work's high physical and psychological demand and low social support have been associated with 20% lower rates of return to work in workers from California who suffered from low-back pain.16 Even after adjustment by severity of the event, Cheadle et al4 (2004) found association between age above 30 years and female sex and duration of the disability benefit. A study with workers on leave due to musculoskeletal diseases found that a positive expectation of return to work was a predictor of the benefit's duration.12 An inverse relation between income and duration of work leave was observed in workers who received benefits due to low-back pain in the United States. 24 Conversely, a study carried out in Brazil with all the health problems found a positive association between the monthly value of the benefit (which indirectly measures the worker's salary) and its duration.b

Disability studies investigate mainly musculoskeletal disorders (MSD). These diseases represent the largest cause of receipt of social security compensations in diverse countries, remarkably when related to work.2,18,19 In Brazil, 48.2% of the benefits granted due to work-related diseases were granted due to MSD in 2006.c Thus, this research focuses on neck and/or upper-limb musculoskeletal disorders (ULMSD) of occupational origin, as a way to reduce differences in characteristics and clinical evolution and to highlight aspects related to prevention capacity.

The present study aimed to analyze factors associated with the duration of disability benefits due to work-related ULMSD.

METHODS

Ambispective cohort study conducted with 563 insured workers from Regime Geral da Previdência Social (RGPS - General Social Security System) who received temporary disability benefits due to work-related ULMSD in the city of Salvador, Northeastern Brazil, in 2008. Eligible individuals were beneficiaries with first entrance in the system in 2008, start of the benefit between 1/1/2008 and 12/31/2008 and diagnoses contained in the International Classification of Diseases (ICD-10) compatible with ULMSD.d Injury resulting from acute trauma and previous history of benefit receipt due to work-related ULMSD in any period were exclusion criteria. The follow-up lasted until 12/31/2009 and the benefit's cessation due to medical decision was considered an event.

The secondary data came from two sources: Sistema Único de Benefícios (SUB, National Benefits System, which is the record of administrative data of Instituto Nacional do Seguro Social [INSS - National Social Security Institute], in which each benefit grant is processed) and a project about temporary disability benefits due to ULMSD developed by the Regional Audit of INSS in Salvador. This project included the RGPS workers whose ULMSD benefits were granted in the Agências da Previdência Social (APS - Social Security Agencies) of Salvador in the period. After the grant of the benefit, the insured workers were summoned by the Audit to answer a questionnaire containing sociodemographic information, occupational history, work demands, characteristics of the current health problem and others. The use of these data was authorized by the management of the Regional Audit of Salvador. The data and the reason for the benefit's cessation were provided by the Regional Audit in January 2010, due to the fact that they were requested after the date that had been set for the termination of the follow-up of the insured workers. The access to the other data occurred in April 2009.

A total of 1,738 benefits were granted due to work-related ULMSD (32% of the occupational benefits, including occupational diseases and accidents). These benefits corresponded to 1,692 workers, among whom 46 received two temporary benefits due to ULMSD in the year and 1,016 were considered ineligible (972 with previous receipt and diagnosis compatible with work-related ULMSD and 44 with injury deriving from acute trauma).

Of the 676 eligible insured workers, 83.3% answered the questionnaire administered by the Regional Audit of the INSS. Of the 16.7% that did not participate, 61 did not go to the Regional Audit after communication by letter or by telephone and 52 were not located. There was a higher proportion of women and older workers among participants in relation to non-participants, but no statistically significant difference was observed in the monthly income paid by the INSS. The median of the benefit's duration was higher to participants compared to non-participants.

The response variable was duration of the disability benefit (interval in days between the beginning and the cessation of the benefit due to the decision of the medical expert of the INSS).

The sociodemographic variables were age, sex, level of schooling, skin color, marital status, employment situation, unionization and socioeconomic position - measured by the ownership of assets and level of schooling of the head of householde: low (classes C, D and E - scores from 0 to 22) and high (classes A and B - scores from 23 to 46).

Psychosocial work demands were measured through the Job Content Questionnaire (JCQ),f translated and adapted by Araújog (2000). Scores were estimated for its three components: psychological demand, control and social support. Each component was analyzed in a dichotomous way (high; low), based on its respective medians. This variable was created through the combination of these three measures:6 low (high support/high control, high control/low demand or high support/low demand); and high (low control/ low support, low control/high demand or low support/high demand). Job dissatisfaction, whose evaluation was based on questions of the JCQ adapted by Fernandesh (2004), was measured by the scores and dichotomously analyzed (high; low) based on the medians.

Physical work demands were defined based on the answers to the questions proposed in the adapted instrumenth referring to repetitive gestures, muscular strength with arms or hands, lifting loads and elevation of the arms above the height of the shoulders. Scores were built by adding the points corresponding to each answer and were analyzed as low exposition and high exposition, with cut-off point in the median.

Other work-related factors were analyzed: employees' turnover in the company and time of employment in the last company (in days).

Factors related to the health problem and to health in general approached pain intensity, measured by the individual him/herself based on his/her perception (scale of zero - absence of pain - to ten - unbearable pain),3 classified into low (< median) and high (> median); duration of the problem (in days) before the receipt of the benefit; having undergone surgery due to the current disease; depression symptoms assessed by the administration of the Patient Health Questionnaire;22 undergoing psychological therapy; comorbidities; and utilization of the Sistema Único de Saúde (SUS - National Health System) to treat the health problem.

The insured worker's expectation regarding return to work was assessed through the question adapted from the Work Ability Index:i "Considering your health, do you think that in two years' time you'll be able to perform your current work?" The expectation was classified into low ("it's improbable" or "I'm not sure") and high ("probable" or "quite probable").

Social security factors involved monthly income paid by the INSS and level of income replacement by the social security (percentage of the net value of the insured worker's last salary replaced by the INSS, classified into up to 100% and higher than 100%).

The factors associated with time up to benefit cessation were identified with survival analysis techniques. The Kaplan-Meier method was used to estimate the survival functions. The identification of factors associated with the duration of the benefit was based on the hazard ratio, which is equivalent to the risk ratio (RR) and respective 95% confidence intervals, and the Cox model was applied. RR > 1 indicated higher rate of benefit cessation and shorter duration of the benefit compared to the reference group. RR were estimated to each descriptor variable, taking a category as referent in bivariate analysis to select the variables to the multiple analysis. The multiple analysis was based on a backward approach, starting from a model with all the variables that presented statistically significant crude risk ratios for α = 0.20. The statistical significance level α = 0.05 was adopted as the criterion for the variables to remain in the model. Level of schooling and monthly income paid by the INSS were excluded from the initial model because they are constructs that directly or indirectly constitute the socioeconomic position. The likelihood ratio test was employed to compare the multiple models. The presupposition of risk proportionality, necessary to the Cox model, was evaluated with the graphical approach and with a statistical test based on the analysis of Schoenfeld residuals.15 The final model was stratified by job dissatisfaction due to the violation of this presupposition.

The management of the databases was performed with EpiInfo, version 6.0 and Stata 7.0 for the conduction of the analysis.

This research was approved by the Research Ethics Committee of the Institute of Public Health of Universidade Federal da Bahia (Process no. 014/2009). Access to the nominal data was restricted to the first author.

RESULTS

The mean age of the population was 39 years (Table 1). The majority of the insured workers was of the female sex (71%), non-white (83%), lived with a partner (65%), came from Class C (64.3%), had studied up to the middle or the end of Secondary School (56.7%) and was composed of employed workers (95%). The mean monthly income paid by the INSS was R$944.23. To 46% of the workers, the income paid by the INSS was higher than their last net salary. The beneficiaries had high control of the work, high psychological demand, high social support, high physical demand and low job dissatisfaction. Workers with negative expectation of return to work predominated (62%). The mean pain intensity that was reported was 9.28, the mean duration of the health problem before the beginning of the benefit was more than two years, the majority did not report having undergone surgery (85%), 42% presented depression symptoms, and 37% used the SUS for medical treatment (Table 2). The insured workers' probability of continuing to receive the benefit was higher than 70% in the first 90 days and 14% after one year (Figure 1). The duration of the benefit varied from six to 730 days, with median of 139 days and mean of 188 days (SD = 151). Considering that the censored cases were included in the calculation of the mean, there was underestimation. At the end of the follow-up, 95% of the insured workers had their benefit terminated, 24 continued on work leave and two had their sickness allowance transformed into disability retirement. The rate of benefit cessation was 35% higher for younger insured workers than for older ones (RR = 1.35; 95%CI 1.14;1.60). Workers with lower level of schooling and those with low socioeconomic position had higher rates of benefit cessation, respectively, 22% (RR = 1.22; 95%CI 0.99;1.49) and 36% (RR = 1.36; 95%CI 1.10;1.69) and, consequently, shorter duration of the benefit. There were no differences in benefit duration in relation to sex, skin color, marital status, employment situation and unionization. Low psychological demand at work increased by 22% the benefit cessation rate (RR = 1.22; 95%CI 1.03;1.45), while high control and job satisfaction reduced the benefit cessation rate by 22% (RR = 0.78; 95%CI 0.66;0.93) and 16% (RR = 0.84; 95%CI 0.71;1.00), respectively. Psychosocial demand, physical demand and turnover in the company had no effect on benefit duration. Workers with positive expectation of return to work had a 22% higher rate of benefit cessation compared to those with negative expectation (RR = 1.22; 95%CI 1.03;1.46). Not reporting comorbidities (RR = 1.19; 95%CI 1.00;1.42) and shorter duration of the health problem before starting to receive the benefit from the INSS (RR = 1.28; 95%CI 1.08;1.52) were associated with benefit cessation. Undergoing surgery due to the health problem, pain intensity, associated depression symptoms, undergoing psychological therapy and utilization of the SUS had no effect on benefit duration. Value of the benefit paid by the INSS lower than or equal to R$ 593.87 increased by 38% the benefit cessation rate in relation to that of higher value (RR = 1.38; 95%CI 1.16;1.63), while income replacement lower than or equal to 100% by the social security increased this rate by 29%, compared to replacement higher than 100% (RR = 1.29; 95%CI 1.09;1.53) (Table 3).

After adjustment by the multiple analysis, the categories of variables associated with benefit cessation and its shorter duration were: low socioeconomic position (RR = 1.29; 95%CI 1.02;1.64), age below 39 years (RR = 1.23; 95%CI 1.03;1.47), high expectation of returning to work (RR = 1,20; 95%CI 1.00;1.44) and level of income replacement by the INSS lower than or equal to 100% (RR = 1.24; 95%CI 1.04;1.47) (Table 4). These were measures of residual effect, after adjustment by all the potential predictors.

DISCUSSION

Low socioeconomic position, age below 39 years, high expectation of returning to work, and income replacement by the INSS lower than or equal to 100% are related to higher benefit cessation rate and to shorter benefit duration.

The shorter duration of the benefit among workers of low socioeconomic position compared to those of high socioeconomic position, which was shown in this study, differs from the findings of investigations carried out in other countries, in which the association between socioeconomic position and benefit duration is observed in the opposite direction. Volinn et al24(1991) examined benefits granted due to low-back pain in the United States and found an inverse relation between income and duration of the work leave. Katz et al13 analyzed factors related to return to work among workers who underwent surgery for carpal tunnel syndrome and observed that individuals with lower income had odds almost four times higher of remaining on leave compared to those with higher income. A literature review showed a strong and consistent inverse association between social class and duration of work leave due to low-back pain, mainly among men.25 However, as in the present study, preliminary analyses of the database of the INSS in Bahia in 2000 showed a positive association between the monthly value of the disability benefit, which indirectly measures the worker's salary, and benefit duration.j These results can reflect inequalities in the local social security, in which the economically privileged individuals have more lasting benefits. Individuals with privileged socioeconomic position would have greater dialog capacity with their employers and with State institutions, and greater knowledge of their rights and of the functioning of social security, which might determine a difference in the utilization of the social security benefits.

The association between expectation of returning to work and benefit duration agrees with other studies about MSD. This association has been found in Canada by Hogg-Johnson & Cole,12 who studied workers with work-related MSD in Ontario, and by Gross & Battié,9 who analyzed patients with chronic low-back pain in Alberta. Expectation of returning to work among patients submitted to surgery due to carpal tunnel syndrome was the most important predictor of absence from work.13 The reason that influences workers' expectation is not exactly known, nor the mechanisms of its association with duration of work leave. A qualitative study with workers with occupational low-back pain showed that the expectation of returning to work reflects four domains: financial and job security, possibility of recurrence of the health problem, social support at the workplace and self-image.21

The level of income replacement by the INSS was a predictor of benefit duration. In the Brazilian social security, the value of the disability benefit received by the insured worker corresponds to 91% of the benefit salary, which corresponds to the mean of the 80% highest salaries of the entire contribution period, duly corrected. Thus, the benefit's value can be lower, equal or higher compared to the insured worker's last salary before the leave. Individuals who received benefits equal to or lower than the value of the last salary before the leave had shorter benefits in relation to those who received benefits with higher value. The higher value of the benefit compared to the salary may be a direct incentive to the worker, thus becoming an attractive condition and influencing the longer duration of the benefit.11,20 On the other hand, inadequate income replacement by the social security system, with value lower than the salary, may make the worker return prematurely to work, with important physical limitations. This does not allow him/her to recover adequately, which may lead to relapses and other work leaves. Loeser et al20 concluded that there is an effect of the level of income replacement by the insurance on the incidence and duration of disability benefits. Another review concluded that the results concerning the association between level of income replacement by the insurance and benefit duration are controversial, possibly due to differences in the contexts in which the studies were conducted.11

Benefits of younger insured workers lasted less, which indicates lower recovery difficulty in this group. Age is one of the most consistent predictors of disability due to occupational health problems.23

Psychological demand, work control, comorbidities and the period in which the health problem was present before the receipt of the benefit were associated with benefit duration, but lost significance in the final model. One of the possible explanations may be the insufficient size of the studied population to detect differences in benefit duration caused by these factors. Analytical approaches with multiple predictors frequently demand an increase in the size of the studied sample.1

The results that were found should be analyzed in light of the limitations of the database; after all, this study used secondary data from the INSS, which may negatively affect the quality of the information. In the present study, the losses represented 16.7% of the selected insured workers. The median of benefit duration was higher to the participants in comparison to non-participants and the difference between the survival curves was statistically significant. The utilization of information restricted to the first benefit of the insured worker was another limitation. Such procedure might underestimate the duration of the disability, because the ULMSD may cause recurrent leaves from work because they are chronic diseases.

Non-strictly medical factors, like socioeconomic position, age, expectation related to returning to work and level of income replacement by the INSS influence the duration of the benefit. These hypotheses should be tested in confirmatory studies. Enhancing the understanding of the process that determines the utilization of the social security/ incapacity for work is fundamental to the development of interventions that reduce the economic, social and personal costs of disability, as well as to face the possibility of social inequality in the utilization of the insurance.

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Correspondence:
Norma Suely Souto Souza
Rua Augusto Lopes Pontes, 1211
Edf. First Tower, Apt 1803
Costa Azul
E-mail: nsouto@uol.com.br

Approved: 12/1/2011

A Paper based on the doctoral dissertation authored by Souza NSS, submitted to the Institute of Public Health of Universidade Federal da Bahia in 2010.
The authors state there are no conflicts of interest.
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Faculdade de Saúde Pública da Universidade de São Paulo São Paulo - SP - Brazil
E-mail: revsp@org.usp.br