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Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. ADDITIONAL DISCLOSURE
  10. Acknowledgments
  11. REFERENCES

Objective

To understand the impact of ankylosing spondylitis (AS) on presenteeism and to explore its relationship to sick leave.

Methods

AS patients completed a questionnaire consisting of sociodemographics, disease characteristics, and work outcomes, including sick leave and presenteeism, assessed by the Work Limitations Questionnaire (WLQ). Associations between a broad range of explanatory variables with the WLQ and AS-related sick leave were assessed by zero-inflated negative binomial and zero-inflated Poisson regressions.

Results

Of 311 employed patients (204 men [65.6%]), 18% had sick leave in the past month. Limitations in meeting time management demands (33.7%), physical demands (30.2%), mental–interpersonal demands (20.2%), and output (19.0%) were noted. With the mean ± SD WLQ index score of 6.7 ± 5.9, the average decrease in work productivity attributable to health was 6.3%; an extra 7.1% of work hours would be needed to compensate for lost productivity. Helplessness, female sex, and impaired health-related quality of life (Ankylosing Spondylitis Quality of Life instrument [ASQoL]) were major contributors to the level of presenteeism (P < 0.01). At-work limitations (WLQ) and lower quality of life (ASQoL) were significantly associated with probability of sick leave, while the length of sick leave was strongly associated with lower educational level and helplessness (P < 0.01), and in some models, also with disease duration and country of residence (P < 0.05).

Conclusion

AS hinders patients' work, mainly in time management and physical demand domains. The WLQ and ASQoL are able to identify patients who incur sick leave. Helplessness contributes independently to the level of presenteeism and the length of sick leave.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. ADDITIONAL DISCLOSURE
  10. Acknowledgments
  11. REFERENCES

The onset of ankylosing spondylitis (AS) occurs typically in the third decade of life, when worker participation is one of the most important social roles of patients. The physical and emotional consequences of AS can limit patients' ability to adjust to different job demands in both paid and unpaid work ([1, 2]). Presenteeism and absenteeism together characterize the main work outcomes. While absenteeism refers to a phenomenon when persons cannot attend their work (either due to temporary sick leave or permanent worker disability), presenteeism refers to the reduced performance or productivity while at work because of health reasons ([3-5]). Both work outcomes are part of the continuum of productivity ranging from fully employed and productive to working with limitations, working with limitations that reduce productivity, sick leave, and ultimately work loss ([6]).

Several self-reported instruments to measure presenteeism have been developed ([7]), with a number of them being used for arthritis (overviews provided by Beaton et al [2009] and Escorpizo et al [2007]) ([6, 8]). Conceptually, individuals score severity and/or duration of at-work limitation or self-rate productivity. Structurally, these instruments are mostly single-item global assessments, whereas only a few are multidimensional. Although self-reported productivity is often linearly related to observed productivity, this assumption of linearity does not seem to be valid and cannot simply be used to calculate the costs of reduced productivity due to presenteeism. The relationship between self-rated limitations or productivity and observed loss of productivity in the work place or for society is likely a complex one ([5]).

The 25-item Work Limitations Questionnaire (WLQ) was designed to capture the overall impact of health-related work limitations ([9]). Being one of the multidimensional instruments, it comprises 4 work demand scales: time demands, physical demands, mental–interpersonal demands, and output demands. The final WLQ index score is calculated as the weighted sum of these 4 scales, where the weights were derived from actually observed productivity. Two features make the WLQ unique. First, the explicit inclusion of the physical demands of the job (although not weighted highest) emphasizes the impact of musculoskeletal disease on worker productivity. Second, based on the WLQ index score, one can estimate the productivity loss of the individual at the work place based on self-reported limitations while at work. The costs of any loss of productivity through presenteeism for the work place or society can then be calculated and can be added to the costs associated with sick leave (Figure 1).

image

Figure 1. Relationship of the health-related and contextual factors of the individual's work limitations/productivity loss (Work Limitations Questionnaire [WLQ]) and productivity in the work place. BASDAI = Bath Ankylosing Spondylitis Disease Activity Index; BASFI = Bath Ankylosing Spondylitis Functional Index; ASQoL = Ankylosing Spondylitis Quality of Life instrument; RAI = Rheumatology Attitudes Index.

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While presenteeism is an important outcome by itself because of its human and economic consequences, the construct would also be of interest when trying to understand the process that leads to sick leave and work disability. Several studies have addressed presenteeism in AS ([10-15]). However, few studies have addressed factors influencing presenteeism and only 2 general population studies revealed a relationship between presenteeism and sick leave ([16, 17]). Although it seems self-evident that presenteeism would precede sick leave and/or that patients who return to work after a period of sick leave might still experience presenteeism, this issue has not received the attention it merits. As such, presenteeism may be useful in clinical practice to identify patients at risk for future sick leave.

In this study, we investigated the type and level of limitations and at-work productivity loss due to presenteeism among AS patients using the WLQ. In addition, we examined factors associated with presenteeism and explored the association between presenteeism and sick leave.

Box 1. Significance & Innovations

  • Limitations at work in patients with ankylosing spondylitis (AS) are substantial. Women and patients with worse health and more helplessness experience more presenteeism.
  • Presenteeism (measured by the Work Limitations Questionnaire) and AS-related quality of life are strongly associated with the probability of sick leave.
  • The length of sick leave is associated with health-related factors (Ankylosing Spondylitis Quality of Life instrument), but also with contextual factors, including educational level, helplessness, and country of residence.

PATIENTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. ADDITIONAL DISCLOSURE
  10. Acknowledgments
  11. REFERENCES

Patients

Patients with AS according to the modified New York criteria ([18]), age >18 years, and under the care of a rheumatologist in Canada or Australia received a postal questionnaire in the context of a research project to assess the burden of AS. The Canadian data set was acquired through participation of academic and community-based centers in Northern Alberta, the Ontario Spondylitis Association, and the Arthritis Society, British Columbia division. The Australian data set was acquired through collaboration with the Austin Spondylitis Clinic in Melbourne, Victoria, Australia, which receives referrals from both general practitioners (60%) and community rheumatologists (40%). Ethics committees of the respective institutions (Health Research Ethics Board, University of Alberta and Human Research Ethics Committee, Austin Health, Melbourne, Victoria, Australia) approved the study protocol and all patients provided informed consent for use of the data for scientific purposes.

Assessment of work outcome

Patients were asked about their employment status: employed (including self- and home employment), not working, or retired (regular retirement or due to AS). For those employed, sick leave was assessed by the number of working days absent due to AS in the last 4 weeks. Finally, patients completed the 25-item WLQ ([9]). The WLQ is a 25-item self-administered questionnaire that asks about the percentage/amount of time (range 0–100%, where 0% = none of the time and 100% = all of the time) in the last 2 weeks in which health or emotional problems interfered with 1 of 25 specific job demands on a 5-point answer scale. Responses generate 4 individual work limitation scales: time, physical, mental–interpersonal, and output scales. The time scale contains 5 items addressing difficulty performing work time and scheduling demands. The physical scale covers 6 items about a person's ability to perform work tasks that involve bodily strength, movement, endurance, coordination, and flexibility. The mental–interpersonal scale has 9 items: 6 items pertain to difficulty performing cognitive job tasks and/or tasks involving the processing of sensory information and 3 items address challenges in interacting with people at work. The fourth output scale contains 5 items concerning decrements in a person's ability to meet demands for quantity, quality, and timeliness of completed work. The sum of weighted (regressed) scores for all 4 WLQ scales form the WLQ index score, which represents the natural log of work productivity. Using the conversion table for the WLQ index score, the productivity impact of health-related work limitations can be further calculated either in terms of percent decrease in productivity (compared to a healthy norm) or as a percent increase in work hours needed to compensate for loss of productivity. Such conversion is based on the assumption that an individual's loss of productivity is frequently related to both the degree to which the demands are performed and actual observed productivity, which was used as an external reference during the validation of the WLQ.

Assessment of explanatory variables

With regard to contextual factors, several variables related to the personal and environmental context of the patients were assessed, including age, sex, country of residence (Canada or Australia), race (dichotomized for analyses as white versus nonwhite), educational level (grouped for further analyses into lower [primary, incomplete or complete high school], middle [college and technical school], or higher [university] educational level), and cohabitation status, which distinguished those living alone from those living with a partner or as a family. Perceived control over the disease (helplessness) was assessed by the Rheumatology Attitudes Index helplessness subscale, comprising 5 items each rated on a 5-point Likert scale, with a total score ranging from 0–25 (where higher scores indicate more helplessness) ([19]).

With regard to body functioning and health characteristics of the respondents, the variables that were chosen represent a variety of body functions and activities, including disease duration, disease activity as measured by the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI; range 0–10, where higher values indicate greater disease activity) ([20]), and physical function as measured by the Bath Ankylosing Spondylitis Functional Index (BASFI; range 0–10, where higher values indicate worse functional status) ([21]). In addition, overall health-related quality of life (QOL) specific for AS was assessed by the Ankylosing Spondylitis Quality of Life instrument (ASQoL) ([22]), which is comprised of 18 questions that cover relevant aspects of QOL, including (as in the BASDAI and BASFI) pain and stiffness, fatigue, physical function, and daily activities, but also aspects of emotional functioning. Each question can be answered by “yes” or “no,” and the total score ranges from 0–1 (where higher values indicate worse QOL).

Statistical analysis

Descriptive statistics summarized the characteristics of employed patients, sick leave, and presenteeism (WLQ). An independent Student's t-test, one-way analysis of variance, chi-square test, or Kruskal-Wallis test was used, as appropriate, to examine differences between groups.

Next, we explored the association between explanatory variables and the WLQ. The explanatory variables comprised the contextual factors and AS-specific characteristics: diagnosis duration and either the BASDAI and BASFI (model 1) or the ASQoL (model 2), in view of the large overlap in content between the ASQoL and both the BASDAI and BASFI. The same 2 models were used for sick leave. To test for an additional role of the WLQ in regard to sick leave, identical models were computed the second time, but now including the WLQ.

Since both dependent variables (the WLQ and sick leave) were skewed to the right with an excess of zeroes (8% of patients had the WLQ equal to 0 and 83% had 0 days absent from work due to AS), classic regression analyses, which assume a normal distribution of the data, could not be performed and nonparametric methods were explored (Poisson, negative binominal, 2-part [hurdle], and zero-inflated models). The count models with zero inflation were the best choice for our models because they gave a significant improvement over alternative models based on the Vuong test ([23]), which compared a zero-inflated Poisson model to the standard Poisson model and compared a zero-inflated negative binomial model to an ordinary negative binomial regression model.

Using zero-inflated models allows for zero values (no sick leave due to AS or the WLQ equal to 0) to be generated by 2 distinct processes, assuming we have 2 groups of patients. The first group, “certain zero,” would always report both sick leave and WLQ as equal to 0. The second group, “not certain zero,” included patients who could report any value for sick leave and the WLQ score, including zero. Based on the likelihood ratio chi-square test, zero-inflated Poisson models were the best choice for sick leave and zero-inflated negative binomial models were the best choice for the WLQ. A comparison of Akaike's and Bayesian information criteria ([24, 25]) identified the best-fit models. All analyses were performed using Stata, version 12 ([26]). Detailed reviews of zero-inflated models and examples of the models' use for presenteeism and sick leave are available in other studies ([27-31]).

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. ADDITIONAL DISCLOSURE
  10. Acknowledgments
  11. REFERENCES

Of 764 patients invited to participate in the study, 522 (68.3%) returned the questionnaire (417 in Canada [69%] and 105 [64%] in Australia), of whom 311 (59.6%) were employed and 52 (9.9%) were retired due to AS. On average, respondents were working for mean ± SD 36.5 ± 15.7 hours/week (Table 1). Of those employed, 56 (18.0%) reported to have had sick leave due to AS in the past month, with a mean ± SD duration of 5.25 ± 7.9 days/month, averaging to mean ± SD 0.9 ± 3.9 days/month among all employed patients. Of 311 employed patients, 19 respondents (6.1%) did not provide data on the WLQ (4 patients because they were sick for 4 weeks), and for 15 patients (4.8%), the WLQ could not be calculated (since more than half of the items in at least one of the domains were not applicable to the patient's job or missing). No differences were noted between the Canadian and Australian participants. Canadian nonrespondents had comparable characteristics to the respondents. These data were not available for Australian nonrespondents.

Table 1. Personal factors, disease characteristics, and work outcomes characterizing the patient sample*
 All patients with paid work (n = 311)Patients with WLQ (n = 277)
ValueNValueN
  1. WLQ = Work Limitations Questionnaire; AS = ankylosing spondylitis; BASDAI = Bath Ankylosing Spondylitis Disease Activity Index; BASFI = Bath Ankylosing Spondylitis Functional Index; ASQoL = Ankylosing Spondylitis Quality of Life instrument.

Personal factors    
Age, mean ± SD years45.3 ± 10.631145.5 ± 10.4277
Male sex, no. (%)204 (65.6)311185 (66.8)277
White, no. (%)268 (94.0)285240 (93.8)256
Canadian, no. (%)231 (74.3)311214 (77.3)277
Educational level, no. (%)    
Lower 83 (26.9)309 72 (26.2)275
Middle100 (32.4)309 91 (33.1)275
Higher126 (40.8)309112 (40.7)275
Living alone, no. (%) 56 (18.0)311 46 (16.6)277
Helplessness, mean ± SD12.03 ± 4.5831011.86 ± 4.52277
Worker participation    
No. of working hours/week, mean ± SD (range)36.5 ± 15.7 (0–90)31137.6 ± 15.4 (0–90)277
Respondents with sick leave during the last 4 weeks due to AS, no. (%)56 (18.0)31147 (17)277
Sick leave in the last 4 weeks, mean ± SD (range) days among those sick5.3 ± 7.9 (0–31)563.2 ± 3.6 (0–20)347
Sick leave in the last 4 weeks, mean ± SD (range) days on average1.0 ± 3.9 (0–31)3110.5 ± 1.9 (0–20)277
Functioning and disability factors    
Diagnosis duration, mean ± SD years14.6 ± 9.8 27414.7 ± 10.0243
BASDAI, mean ± SD3.7 ± 2.23103.6 ± 2.2276
BASFI, mean ± SD3.0 ± 2.33092.8 ± 2.2275
ASQoL, mean ± SD5.3 ± 4.83115.0 ± 4.7277

Work limitations were present in all work domains (Table 2). AS patients experienced the greatest impact on time management and physical demands, followed by mental–interpersonal and output demands. With a mean ± SD of 6.7 ± 5.9, these limitations resulted in a decrease of at-work productivity of 6.3% ± 5.3% compared to a healthy norm, or a 7.1% ± 6.5% increase in work hours necessary to compensate for productivity loss.

Table 2. Results of the time impaired in the different WLQ scales and estimated impact on productivity (n = 277)*
 WLQ
  1. Values are the mean ± SD. WLQ = Work Limitations Questionnaire.

WLQ 1: time management (range 0–100)33.7 ± 32.5
WLQ 2: physical demands (range 0–100)30.2 ± 27.8
WLQ 3: mental–interpersonal (range 0–100)20.2 ± 24.2
WLQ 4: output demands (range 0–100)19.0 ± 24.7
WLQ score (range 0–28.6)6.7 ± 5.9
Decrease in productivity (compared to healthy), % (range 0–24.9)6.3 ± 5.3
Increase in work hours to compensate for productivity loss, % (range 0–33.1)7.1 ± 6.5

The results of zero-inflated negative binomial and zero-inflated Poisson models are shown in Tables 3-5. The tables contain 2 parts: the upper (continuous) part, representing the variables predicted by a full model, where the WLQ score or duration of sick leave due to AS is not always zero (“not certain zero” group); and the lower (inflated) part, the logistic model that predicts whether or not a patient would always report the WLQ or duration of sick leave due to AS equal to zero (“certain zero” group). Coefficients (“coef”) in the upper part of the zero-inflated negative binomial and zero-inflated Poisson models correspond to negative binominal and Poisson regression coefficients and should be interpreted as follows: for each unit increase in the corresponding predictor, the expected WLQ score or number of sick days changes by a factor of exp (“coef”), or factor (“e∧b”), shown following the SE. The lower part includes logit coefficients, which predict the odds of a patient belonging to a “certain zero” group (for each unit increase) that also changes by a factor of exp (“coef”), or factor (“e∧b”).

Table 3. Association with presenteeism using zero-inflated negative binominal regression (n = 277)*
WLQ index scoreModel 1: BASDAI and BASFI as health variablesModel 2: ASQoL as health variable
Coef.SEe∧bCoef.SEe∧b
  1. WLQ = Work Limitations Questionnaire; BASDAI = Bath Ankylosing Spondylitis Disease Activity Index; BASFI = Bath Ankylosing Spondylitis Functional Index; ASQoL = Ankylosing Spondylitis Quality of Life instrument; coef. = coefficient; e∧b = for count equation: factor change in expected count for those not always zero, for logit equation: factor change in odds of belonging to certain zero group; N/A = not applicable.

  2. a

    P < 0.01.

  3. b

    P < 0.001.

  4. c

    P < 0.05.

Continuous part of the model      
Country, Canada−0.050.140.950.010.141.07
White, yes−0.220.250.80−0.280.260.76
Education, high−0.020.120.98−0.130.120.88
Disease duration−0.000.010.990.000.011.00
Male sex, yes−0.34a0.110.71−0.32a0.110.72
Living alone, yes−0.020.140.980.070.141.07
Age0.0110.011.010.010.011.01
Helplessness0.06b0.011.060.05a0.021.05
BASDAI0.060.031.06N/AN/AN/A
BASFI0.010.031.01N/AN/AN/A
ASQoLN/AN/AN/A0.05b0.011.05
_cons0.83c0.401.11a0.42
Inflated part of the model      
Helplessness−0.220.150.80−0.150.220.86
BASDAI−0.420.430.65N/AN/AN/A
BASFI−5.804.120.00N/AN/AN/A
ASQoLN/AN/AN/A−1.050.930.35
_cons2.681.66−0.361.61
/lnalpha0.92b0.15 −0.92b0.16 
Alpha0.390.06 0.000.06 
Table 4. Association of different variables with sick leave by zero-inflated Poisson regression, excluding the Work Limitations Questionnaire index score (n = 244)*
Number of sick daysModel 1: BASDAI and BASFI as health variablesModel 2: ASQoL as health variable
Coef.SEe∧bCoef.SEe∧b
  1. BASDAI = Bath Ankylosing Spondylitis Disease Activity Index; BASFI = Bath Ankylosing Spondylitis Functional Index; ASQoL = Ankylosing Spondylitis Quality of Life instrument; coef. = coefficient; e∧b = for count equation: factor change in expected count for those not always zero, for logit equation: factor change in odds of belonging to certain zero group; RAI = Rheumatology Attitudes Index; N/A = not applicable.

  2. a

    P < 0.05.

  3. b

    P < 0.001.

  4. c

    P < 0.01.

Continuous part of the model (number of sick days)      
Country, Canada0.67a0.271.960.65a0.261.92
White, yes−0.910.630.40−0.710.610.49
Education, high−0.47b0.1230.62−0.37b0.110.69
Disease duration−0.020.010.98−0.020.010.98
Male sex, yes0.150.291.170.190.281.21
Living alone, yes0.090.321.10−0.080.280.93
Age0.010.011.010.010.011.01
Helplessness (RAI)0.09b0.031.100.11c0.031.11
BASDAI0.040.081.04N/AN/AN/A
BASFI0.020.731.03N/AN/AN/A
ASQoLN/AN/AN/A0.010.041.01
_cons0.300.72−0.280.65
Inflated part of the model (incurring no sick leave)      
Helplessness−0.020.050.980.050.051.05
BASDAI0.040.131.04N/AN/AN/A
BASFI−0.150.120.86N/AN/AN/A
ASQoLN/AN/AN/A−0.16c0.050.85
_cons1.76a0.711.51a0.67
Prob>χ20.00b  0.00b  
Table 5. Association of variables with sick leave using zero-inflated Poisson regression, including the WLQ (n = 223)*
Number of sick daysModel 1: BASDAI and BASFI as health variablesModel 2: ASQoL as health variable
Coef.SEe∧bCoef.SEe∧b
  1. WLQ = Work Limitations Questionnaire; BASDAI = Bath Ankylosing Spondylitis Disease Activity Index; BASFI = Bath Ankylosing Spondylitis Functional Index; ASQoL = Ankylosing Spondylitis Quality of Life instrument; coef. = coefficient; e∧b = for count equation: factor change in expected count for those not always zero, for logit equation: factor change in odds of belonging to certain zero group; RAI = Rheumatology Attitudes Index; N/A = not applicable.

  2. a

    P < 0.01.

  3. b

    P < 0.001.

  4. c

    P < 0.05.

Continuous part of the model (number of sick days)      
Country, Canada0.540.321.710.70a0.292.02
White, yes−0.910.680.40−0.690.690.49
Education, high−0.48a0.160.62−0.49b0.140.61
Disease duration−0.030.020.97−0.04a0.020.95
Male sex, yes0.120.341.130.160.291.17
Living alone, yes−0.070.390.93−0.410.340.66
Age0.010.021.010.020.011.02
Helplessness (RAI)0.11c0.051.120.160.041.17
BASDAI0.050.111.05N/AN/AN/A
BASFI−0.020.080.98N/AN/AN/A
ASQoLN/AN/AN/A−0.020.040.98
WLQ−2.352.670.09−1.132.070.58
_cons0.710.84−0.430.75
Inflated part of the model (incurring no sick leave)      
Helplessness0.050.061.060.140.071.15
BASDAI−0.050.140.95N/AN/AN/A
BASFI−0.080.130.92N/AN/AN/A
ASQoLN/AN/AN/A−0.16a0.0590.85
WLQ13.48a4.670.48−12.46a4.240.85
_cons2.03a0.781.390.79
Prob>χ20.00a  0.00b  

For the WLQ, there were no variables identifying patients who would never report presenteeism. However, a 1-unit increase in helplessness (in models 1 and 2) or ASQoL (model 2) would increase the expected WLQ by a factor of 1.05 (holding all other factors constant in the model), and the expected WLQ for men would be 0.7 times that for women. The BASDAI and BASFI did not contribute to the level of the WLQ, but in this model, the association of WLQ with helplessness was stronger (Table 3).

For AS-related sick leave, the ASQoL (model 2) but not the BASDAI and/or BASFI (model 1) would be able to distinguish a group of patients more likely not to have any sick leave. A 1-unit increase in the ASQoL decreased the odds of not having sick leave due to AS by a factor of 0.85, holding all other variables constant. For sick leave duration, a higher educational level decreased the expected number of sick days by a factor of 0.6–0.7, as compared to a lower educational level, whereas living in Canada (and not in Australia) or feeling more helplessness increased the duration of AS-related sick leave by factors of 1.9 and 1.1, respectively, holding all other factors constant (Table 4).

The WLQ was also able to correctly identify patients who would never have sick leave. A 1-unit increase (worsening) in the WLQ decreased the odds of incurring no sick leave by 0.5 (model 1 with BASDAI and BASFI) and 0.8 (model 2 with ASQoL), holding all other variables constant. However, the WLQ was not associated with the duration of AS-related sick leave. Variables associated with the duration of AS-related sick leave changed slightly when adding the WLQ to the models. In model 2, a 1-year increase of disease duration was associated with a decrease in duration of AS-related sick leave by a factor of 0.9, holding all other factors constant. Living in Canada (model 1) and helplessness (model 2) became insignificant (Table 5).

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. ADDITIONAL DISCLOSURE
  10. Acknowledgments
  11. REFERENCES

The WLQ proved to be a valuable self-reported instrument to assess limitations across several job demands and, at the same time, estimate at-work productivity loss in patients with AS who had a paid job. Patients with AS experienced limitations in time demands (work without breaks) and physical demands (standing, walking) for ∼30% of their work time and experienced limitations in mental–interpersonal (concentrating, client friendliness) and output demands for ∼20% of their work time. These limitations would lead to a 6.3% decrease in worker productivity as compared to healthy norms or a 7.1% increase in working time necessary to compensate for productivity loss while at work.

Only 2 other studies have reported on the WLQ in AS. Among 80 patients, Rohekar and Pope reported slightly more output demands (33% of the time), and as a consequence, a slightly higher loss of worker productivity at 8.3% ([13]). Healey et al applied the WLQ-16 (16 items across the same 4 scales) among 315 employed patients with AS, reported 18.9 as the mean WLQ score of the 4 scales, and confirmed the largest impact of AS on physical demands of the job ([14]). This figure cannot be directly compared to the values of the WLQ index score derived from the 25-item questionnaire, but a crude conversion would yield a total WLQ index score equal to 4.5, which would be somewhat lower than the WLQ index score of 6.3 in our study.

Although we could not identify any factors that were associated with the likelihood of any presenteeism, female participants and patients with more helplessness or worse health-related quality of life (ASQoL) had higher WLQ index scores. Interestingly, when sick leave was the outcome, the WLQ in addition to the ASQoL were associated with the likelihood of taking sick leave. The length of sick leave, however, was not influenced by disease-related variables or by the WLQ, but was related to contextual factors, including educational level, helplessness, and country of residence. When studying the association between health-related variables and presenteeism or sick leave, we decided not to include the ASQoL, BASDAI, and BASFI together in our models because of large content overlap. While the BASDAI and BASFI had no role in any of the analyses, the ASQoL was relevant when identifying patients who could have sick leave, as well as when explaining the level of presenteeism. It should be noted that the ASQoL addresses not only pain, fatigue, and physical function, but also the emotional aspects related to the disease. Since the WLQ comprises specific scales that not only address physical load and output, but also account for mental and interpersonal demands, it is not surprising that the ASQoL better explains the variation in the WLQ scores. At the same time, the inclusion of emotional functions in the ASQoL must have an important additional contribution to the decision to take sick leave beyond the pain and functional limitations.

Our study adds to the evidence of the relationship between the personal context of patients and presenteeism or sick leave. This is important, since many studies that measured paid productivity loss in patients with inflammatory arthritis did not evaluate the impact of contextual factors ([32]). Helplessness in particular, a personal factor, appeared to be an important variable associated with the level of presenteeism and the duration of sick leave. Helplessness is not often included in outcome studies, but whenever it was explored, it seemed to relate strongly to disease activity ([33]), physical function ([34]), patient acceptable symptom state ([35]), and overall health-related QOL ([36]), and may even serve as a mediator of the relationship between disease activity and functional limitations ([37]). In the literature on work outcomes in AS, Healey et al confirmed that lower self-efficacy, but also increasing age, anxiety, depression, and disease activity, contributed to the WLQ-16 ([14]). The importance of helplessness in our study and of self-efficacy (the counterpart of helplessness) in the study by Healey et al ([14]) in relation to presenteeism and sick leave raises questions as to the extent it will be possible to change an individual's helplessness into a more proactive attitude toward work. Moreover, since we showed that presenteeism is associated with sick leave, assessment of presenteeism might be a useful approach for identifying patients at risk of sick leave and identifying patients who may benefit from timely intervention to prevent sick leave. A review of interventions directed at enhancing adaptive and active coping was disappointing with regard to a true change in behavior ([38]). However, such interventions have, to our best knowledge, not yet been performed in patients with inflammatory rheumatic diseases who experience presenteeism.

In the literature, few studies have addressed the relationship between presenteeism and absenteeism. Using the sample of 2,983 middle-aged workers, Janssens et al (2013) showed (using a single-item global assessment of presenteeism) that presenteeism was related to different durations in future sick leave ([17]). Another study by Allen (2008) used structural equation modeling based on a data set of 17,821 working respondents (collected using a health risk appraisal) to describe and predict productivity loss. It was also shown that presenteeism, assessed by the WLQ, correlated positively with absenteeism ([16]).

The WLQ links the amount of time that patients experience limitations at work to their at-work productivity. The conversion, which is based on observed performance at work, makes clear that the amount of time worked with limitations does not equal the reduction in productivity. This raises questions regarding the validity in terms of estimation of productivity loss of the instruments that assess productivity loss and often use 0–10 visual analog scales (VAS). A study among 73 employed patients under rheumatologic care reported an AS-related work efficiency of 7.7 on a 0–10 VAS, which would suggest a productivity loss of 23% ([10]). In the same study, patients indicated they would need 1.9 hours per 2 weeks (0.8 hour per week) to catch up with unfinished work. Given that the average working hours in this study was 37.6 hours/week, this would represent a productivity loss of 2.1%. This would be much lower than 23% based on the estimation using the VAS, but also lower than the estimated 7.1% in this study using the WLQ. This highlights the large variation in the available approaches when estimating disease-related productivity loss, an issue receiving much attention among outcome researchers.

The main limitation of our study is the cross-sectional nature, which did not allow us to examine whether at-work limitations preceded or followed sick leave. Both likely occurred, but prospective studies, preferably with a longitudinal design, are needed to understand whether presenteeism can really be used as a predictor of sick leave. Also, we had no information on the type of work and level of physical or mental workload that are necessary to explore the validity of the WLQ index scores across different job types, nor did we collect data on possible compensation mechanisms for the productivity loss of the individual at the work place or the impact of an individual's productivity loss on productivity of the team. Finally, our study did not include a single global measure to assess presenteeism. One other study ([17]) also suggested that single items are associated with sick leave. However, a study comparing the discriminative and predictive performance of multidimensional and single-item global instruments for sick leave would be necessary. A single-item global approach would have the advantage of being more feasible in observational cohorts and clinical trials.

In summary, the WLQ provides insight into the relationship between the perceived amounts of time worked and limitations across several job demands and links it with the resulting at-work productivity loss. The strong relationship between helplessness/lack of control and work limitations supports the importance of the biopsychosocial model of a disease when understanding the level of at-work restrictions. Our findings suggest that assessment of at-work limitations/productivity loss may constitute a useful instrument for identifying persons at risk of sick leave. These individuals might benefit from an intervention, which should ideally include timely efforts to improve feelings of helplessness in order to prevent sick leave.

AUTHOR CONTRIBUTIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. ADDITIONAL DISCLOSURE
  10. Acknowledgments
  11. REFERENCES

All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be published. Dr. Gordeev had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study conception and design. Maksymowych, Boonen.

Acquisition of data. Maksymowych, Schachna.

Analysis and interpretation of data. Gordeev, Maksymowych, Schachna, Boonen.

ROLE OF THE STUDY SPONSOR

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. ADDITIONAL DISCLOSURE
  10. Acknowledgments
  11. REFERENCES

Schering-Plough Canada had no role in the study design or in the collection, analysis, or interpretation of the data, the writing of the manuscript, or the decision to submit the manuscript for publication. Publication of this article was not contingent upon approval by Schering-Plough Canada.

Acknowledgments

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. ADDITIONAL DISCLOSURE
  10. Acknowledgments
  11. REFERENCES

The authors would like to thank Dr. Erica Richardson and Ms Katharine Footman for English editing.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. ROLE OF THE STUDY SPONSOR
  9. ADDITIONAL DISCLOSURE
  10. Acknowledgments
  11. REFERENCES
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