Centre for Addiction and Mental Health, Department of Psychiatry, University of Toronto, Toronto, Ontario
Department of Epidemiology and Biostatistics, University of Western Ontario, London, Ontario
Centre for Addiction and Mental Health, Department of Psychiatry, University of Toronto
Institute for Clinical Evaluative Sciences, Toronto, Ontario
Centre for Addiction and Mental Health, Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada
Correspondence: Dr Carolyn S. Dewa, Centre for Addiction and Mental Health, Health Systems Research and Consulting Unit, 250 College St, Toronto, Ontario M5T1R8, Canada. Tel: (416) 535 8501 ext. 4101; fax: (416) 979 4703; e-mail: carolyn_dewa{at}camh.net
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ABSTRACT |
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Aims To address two questions: first, is prescription of antidepressants in accordance with published clinical guides associated with better disability outcomes, and second, what is the relationship between guideline-concordant antidepressant prescription and length of disability?
Method An observational study was conducted using administrative data from three major Canadian financial and insurance sector companies. Short-term disability and prescription drug claims records for 19961998 were linked for workers receiving depression-related short-term disability benefits during that time.
Results Recommended first-line agents and recommended doses were
significantly associated with return to work (2=6.64,
P<0.036). In addition, among those who returned to work, early intervention
was significantly associated with a shortened disability episode
(ß=-24.1; 95% CI -34.4 to -13.8).
Conclusions Depression-related workplace disability is a problem for which there is no simple solution. These results provide an additional piece to the puzzle of helping workers disabled by depression to return to work.
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INTRODUCTION |
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Much of the literature on labour market disability focuses on the impact of workplace factors on productivity, particularly the relationship between stress and job performance (Van der Heck & Plomp, 1997) and the role of workplace support systems on disability outcomes (Akabas, 1995). Only a handful of studies have examined the relationship between antidepressant use and outcomes in the workplace. Using data from a clinical trial, Berndt et al (1998) found evidence of a positive relationship between workers' self-perceived low productivity and severity of depression. They also observed that the use of antidepressants (sertraline and imipramine) had a significant impact on the severity of depression. One might therefore conclude that there is an association between antidepressant treatment and workplace functioning. However, Berndt et al did not directly test the impact of antidepressant treatment on workplace functioning, stopping short of examining the direct relationship between antidepressant use and productivity.
Mintz et al (1992) pooled data from ten studies and used the Social Adjustment Scale in an attempt to measure the direct impact of treatment on productivity. They found that their productivity measure was positively associated with treatment, and also identified symptom remission and length of treatment as the most important predictors of work impairment. However, their measure for productivity is difficult to translate into policy recommendations.
Using administrative data to examine the relationship between absenteeism and treatment, Claxton et al (1999) observed differences between various antidepressants in terms of mean lost work days. Comparing two types of antidepressants tricyclic antidepressants and selective serotonin reuptake inhibitors (SSRIs) they found a lower average number of days absent for the group using SSRIs. These results offer an important first step towards understanding the impact of antidepressant treatment on absenteeism. However, they did not look at or control for other factors that could also be associated with absenteeism, such as age, gender and pattern of antidepressant use.
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METHOD |
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Claims were managed by company occupational health departments. Thus, disability outcomes were identified using occupational health records. The primary information sources were company short-term disability claims, prescription drug claims and occupational health department records. Because of its smaller size, claims from one company were taken for short-term disability episodes beginning between January 1996 and December 1998. For the remaining two, data were abstracted for claims beginning in 1997 or 1998.
Study population
Cases included in our analysis met three criteria. First, based on company
criteria for short-term disability benefits, claimants had depression-related
absences from work for at least 10 consecutive work days prior to their
disability leave (starting sample n=1521). The second criterion
required claimants to have used their prescription drug benefits at least once
during the study period for any type of prescription. Sixty cases were
excluded because we could not ascertain whether the absence of antidepressant
claims was due to the individual not filing a prescription for an
antidepressant, not receiving a prescription for an antidepressant, or not
using the company's drug benefit plan. The third prerequisite was that the
claimant had no more than one short-term disability episode within the
previous 12 months (final sample n=1281). This criterion helped to
ensure that the episode included in the data-set was a distinct episode rather
than a continuation of an earlier one. About 12% of the claimants had had more
than one short-term disability episode in the prior 12 months.
Short-term disability outcomes
Three major categories of disability outcomes were observed:
Employees in all three participating companies were eligible for long-term disability benefits after a total of 6 months on short-term disability.
Length of short-term disability
Days on short-term disability benefits were the number of days between the
first and last day of the disability episode. The end of the disability
episode was marked by the person's return to work either full-time or
part-time.
Defining recommended antidepressant treatment
Recommended antidepressant treatment was based on the guidelines published
by the Canadian Network for Mood and Anxiety Treatment (CANMAT; 1999). This
organisation is a national network of Canadian health care professionals in
research, academic and clinical centres set up to improve the treatment of
individuals with mood and anxiety disorders. These guidelines are written for
physicians practising in general medical settings. From patterns of drug use
recorded during the 200 days following the initiation of the short-term
disability episode, we developed three variables to characterise different
aspects of drug use.
Complexity of depression indicators
To reflect the number of symptoms reported by the claimants, we created a
count of the number of depression-related symptoms recorded on the short-term
disability application form. Information was abstracted from occupational
health records using a checklist covering the major DSMIV depressive
symptom categories (American Psychiatric
Association, 1994).
In previous work we had observed that despite concordance with guideline-recommended first-line agents and use within recommended time frames, there is a group of users who experience a complex course of antidepressant use. These complex patterns have been reported by Claxton et al (1999) and Thompson et al (1996). There is evidence that this complexity is associated with a greater need for high-intensity health services. This, in turn, may be linked to the severity of the episode. For example, Thompson et al (1996) observed that those who switched or augmented their antidepressant use had more in-patient hospital use. These findings were corroborated by Dobrez et al (2000), who reported that these groups of patients use more health care services overall. Dewa et al (2003) observed patterns suggesting a greater severity of illness and its resistance to treatment: for example, those who switched and those who had augmented use on average reported a greater number of symptoms than those who either had one antidepressant fill or used one antidepressant exclusively. This suggests that the former two groups might have had more severe depression, leading to more problems with treatment. On the basis of previous research (Dewa et al, 2003), we created four pattern variables to capture the complexity of antidepressant use.
Analyses
We began by examining bivariate relationships between variables. Rates of
the three disability outcomes were calculated per 100 persons. The strength of
the associations between these rates and claimant characteristics was tested.
The chi-squared test was employed to examine the strength of the association
between the outcomes and dichotomous variables. Two-sided t-tests
were used to test the associations between continuous variables and
antidepressant use patterns.
A two-part multivariable model was used to examine the effect of guideline-recommended use of antidepressants on return to work. In the first part of the analysis, we controlled for complexity of the depression and demographic characteristics using a logistic regression model to test whether use of antidepressants concordant with recommended use is associated with greater likelihood of returning to work. In the second part, we explored the relationship between recommended use and days on short-term disability. For this part of analysis, the study population was subdivided to include only those who returned to work (n=997). Using an ordinary least squares regression model, we estimated the association of guideline-recommended use on length of short-term disability.
Because there may exist non-random company-specific factors associated with either return to work or length of disability, company-specific fixed effects were included in both the first and second part of the model. Under ideal conditions, we would control for these non-random factors by including variables that are correlated with disability outcomes and vary between companies. However, given the limitations inherent in the data, we were unable to adjust explicitly for all company factors and their contribution to the disability outcomes. Instead, company-specific fixed effects were used to account for workplace characteristics without actually measuring them. The company fixed effects allowed us to adjust our estimates for unobserved company-related heterogeneity.
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RESULTS |
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Our severity indicators also suggested that there were differences in the severity of symptoms experienced by claimants who did and did not return to work. Those who returned to work reported significantly fewer symptoms than those who either went on to long-term disability benefit (mean difference 2.04, 95% CI 1.62.5; t=1183, P<0.0001) or left their employment (mean difference 1.2, 95% CI 0.71.8; t=4.27, d.f.=1091, P<0.0001).
More than half of the claimants studied (56%, 95% CI 53.258.6) used
antidepressants. However, antidepressant use differed between the groups who
did and did not return to work (Table
2). There was a higher proportion of antidepressant use among
those who went on to long-term disability benefits as opposed to those who
returned to work (difference 19.6%; 95% CI 12.626.8;
2=24.84, d.f.=1, P<0.0001). Furthermore, there was
a significant difference in the average number of days on short-term
disability benefits between the two groups. Those who did not use
antidepressants received short-term disability benefits for an average of 77.3
days (95% CI 72.482.1), whereas for those who did the average was 104.7
days (95% CI 99.9109.5): mean difference 27.4, 95% CI 34.320.7;
t=7.92, d.f.=1259, P<0.0001).
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In addition, claimants who used antidepressants and returned to work
differed in their patterns of antidepressant use. Of those who used one
antidepressant exclusively throughout their short-term disability episode, a
greater proportion returned to work (difference 11.7%, 95% CI 5.118.4;
2=12.57, d.f.=1, P<0.0001). In contrast, a
significantly large proportion of those who either switched antidepressants
(difference 16.3%, 95% CI 8.024.5;
2=17.21, d.f.=1,
P<0.0001) or augmented their use (difference 15.3%, 95% CI
4.226.5;
2=8.72, d.f.=1, P<0.003) left
their employment.
Among antidepressant users, a majority were concordant with guideline
recommendations in terms of type of antidepressant, dose and timing. However,
there were differences between outcome groups. Compared with the two groups
who did not return to work, a significantly larger proportion of the group who
returned to work used first-line antidepressants (difference 5.6%, 95% CI
0.211.0; 2=5.13, d.f.=1, P<0.023) and
guideline-recommended dosages (difference 10.9%, 95% CI 2.818.9;
2=7.93, d.f.=1, P<0.005).
In the first regression model, we examined the extent to which return to
work is associated with worker characteristics, depression complexity or
antidepressant use (Table 3),
using a logistic regression. The model's goodness of fit was tested using the
HosmerLemeshow test. We could not reject the null hypothesis that there
was an adequate fit with the model (2=3.74,
P<0.88). The results of the first part of the model are reflective
of those found in the bivariate analyses. The number of symptoms reported was
a significant factor associated with return to work. The larger the number of
symptoms, the smaller the odds ratio (OR=0.83, 95% CI 0.780.89,
P<0.0001). In addition, the complexity of use indicator variables
suggested that as antidepressant use became more complex, the odds of
returning to work became lower (e.g. for augmented use, OR=0.16, 95% CI
0.0690.39, P<0.0001). Age also had a significantly negative
impact on return to work (OR=0.98, 95% CI 0.970.9998,
P<0.047). Finally, although the guideline recommendation
indicators suggested that each had a positive impact on return to work,
individually none was statistically significant. However, this may be due to
the fact that they are highly related to one another (i.e. there is
multicollinearity among the variables), making it difficult to isolate the
impacts of the variables (Gujarati,
1995). Indeed, the likelihood ratio test of the joint significance
of first-line agent use and recommended dose showed evidence that together
they are associated with return to work (
2=6.64, d.f.=2,
P<0.036).
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In the second part of the model, we used an ordinary least squares regression model to examine the factors associated with the length of the short-term disability among those who returned to work. To test the robustness of our results, we transformed the values for days on short-term disability benefit using both log and square root transformations and compared these results with those using the untransformed values. We found similar results for all three models. For ease of interpretation, we have presented the results using the untransformed values for numbers of short-term disability days.
Overall, we observed that the mean short-term disability episode was 74.2 days (95% CI 71.077.4). After controlling for demographic characteristics, severity, complexity and company effects, we found that the use of antidepressants within 30 days of the start of the disability episode was significantly associated with the length of episode (ß=-24.1; 95% CI -34.4 to -13.8). On average, compared with those who either delayed use or did not use antidepressants, there was a 24 day decrease in the length of the short-term disability episode. As in the first part of the model, the results suggested that the number of reported symptoms (ß=7.7, 95% CI 6.39.0) and complexity of use (e.g. for augmented use ß=61.6, 95% CI 37.285.9) were associated with increased length of disability. In addition, the company fixed effects indicated that there was a significant difference in length of disability episode among the participating companies (company 1, ß=-39.7, 95% CI -55.7 to 23.6; company 2, ß=-20.6, 95% CI -27.7 to -13.6). Finally, the guideline recommendation indicators for first-line agent use and dose in combination were positively associated with return to work; however, once again, individually neither was statistically significant.
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DISCUSSION |
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First-line agents and return to work
Workers using recommended first-line agents and recommended doses were
significantly more likely to return to work rather than to claim long-term
disability benefits or leave their employment. These results are congruent
with the hypothesis that antidepressants can play an important part in the
ability of employees to resume work.
Early intervention
Early intervention and return to work
Early intervention was significantly associated with a shortened disability
episode among employees on depression-related disability benefits who had at
least one antidepressant prescription claim and eventually returned to work.
Our estimates indicate that early intervention is associated with a reduction
in disability episode of about 3 weeks.
Preliminary estimates of savings associated with early
intervention
Given the average weekly wage for this sector is about $1011, including 30%
for benefits (Statistics Canada,
2002), early intervention represents a potential average saving of
approximately $3500 (based on ß=-24.1, 95% CI -34.4 to -13.8, the range
of savings would be $20005000) in terms of reduction in lost
productivity per employee claiming depression-related short-term disability
benefits (all values quoted in Canadian dollars). For employees in our study
who began using antidepressants more than 30 days after the start of their
episode and returned to work, total savings could have translated into nearly
$539 000 (range $268 000875 000). It should be noted, however, that
this is an estimate based on this sample and does not include the expense of
treatment and other societal costs. Additional research is needed to
corroborate these findings and give a more comprehensive estimate of potential
societal benefits.
Antidepressant use
Our findings indicate that about 40% of individuals receiving short-term
disability benefits related to depression do not use antidepressants.
Application of quality measures such as those currently used by the Health
Employer Data and Information Set (Druss
et al, 2002) suggests that many employees do not receive
treatment. However, our findings indicate that there might be other
interpretations.
Potential role of complexity and severity of depression
The apparent absence of antidepressant use might be indicative of a
difference in the complexity of depression experienced. For example, from past
analyses we found that about three-quarters of those who did not use
antidepressants did not have them included as part of the short-term
disability care plan reported by their physician. In addition, on average,
they also reported lower numbers of symptoms than those who used
antidepressants (Dewa et al,
2003). Finally, those who did not use antidepressants returned to
work sooner than those who did. Do the absence of antidepressants in the
initial treatment plan, the fewer number of symptoms and the faster return to
work suggest that those who do not use antidepressants have a less complex
illness course? Or could these factors be indicative of lesser severity of
depression than in their counterparts who used antidepressants? Perhaps these
individuals are relying on other types of intervention, such as counselling?
Does the lack of antidepressant use reflect a resistance to adopting a sick
role and consequently a more rapid return to work? These questions will be
important to address in future follow-up studies.
Limitations
As with most administrative database studies, our results are limited by
the accuracy of the diagnosis on the claim forms
(Browne et al, 1998).
In an ideal world we would have conducted a clinical assessment of all
individuals in the study to verify whether they were suffering from a
disabling episode of depression. However, in the interests of feasibility and
maintaining worker anonymity, we chose to study the population identified as
having depression rather than those confirmed with depression. In addition, we
focused on only one aspect of treatment for depression. In future studies it
will be helpful to understand the roles of other treatments such as
psychotherapy. Disability management practices and preventive interventions
are other areas worth exploring. Furthermore, our reliance on administrative
data constrains our ability to comment on compliance
(Edgell et al, 1999).
It is assumed that workers who filled prescriptions also took their
medications. To the extent that this is valid, our measures of use reflect a
combination of partial compliance and physicians' prescribing patterns.
Finally, our study focused on workers who took depression-related disability
leave. Consequently, although this study represents an important first step in
exploring the role of antidepressants in influencing depression-related
short-term disability, the limitations associated with an observational study
design make our results more exploratory than definitive. We cannot comment on
the precise mechanism that results in return to work: other factors, related
to receipt of guideline treatments, may affect outcomes. Although we have
tried to adjust for such confounders by including variables representing
socio-demographic characteristics, guideline-recommended use, type of company
and degree of complexity, the administrative data limit the extent to which
this could be done. Use of a randomised controlled trial design would decrease
the opportunity for such a sample selection bias.
Future research
Our findings point to a number of avenues for future research. For example,
are similar results observed in all business sectors? Do the same patterns of
use apply to employees who use antidepressants but do not claim disability
benefits? What is the role of other, non-pharmaceutical treatments? What are
the critical components of disability management programmes? What
environmental factors affect return to work?
Depression in the workplace is a problem for which there is no simple solution. The nature of the disability and its treatment are complex. This study takes advantage of a unique link between occupational health records and drug benefit claims data to examine one aspect of treatment. The results do not prove a causal link between recommended treatment and better disability outcome (i.e greater likelihood of return to work or shorter duration of disability). However, they provide additional leads to answering the important questions of how to help people disabled by depression return to work.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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Received for publication February 12, 2003. Revision received June 9, 2003. Accepted for publication June 19, 2003.
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