The impact of a sick pay waiting period on sick leave patterns

Collider Bias in Administrative Workers' Compensation Claims Data: A Challenge for Cross-Jurisdictional Research

PURPOSE

Workers' compensation claims consist of occupational injuries severe enough to meet a compensability threshold. Theoretically, systems with higher thresholds should have fewer claims but greater average severity. For research that relies on claims data, particularly cross-jurisdictional comparisons of compensation systems, this results in collider bias that can lead to spurious associations confounding analyses. In this study, I use real and simulated claims data to demonstrate collider bias and problems with methods used to account for it.

METHODS

Using Australian claims data, I used a linear regression to test the association between claim rate and mean disability durations across Statistical Areas. Analyses were repeated with nesting by state/territory to account for variations in compensability thresholds across compensation systems. Both analyses are repeated on left-censored data. Simulated claims data are analysed with Cox survival analyses to illustrate how left-censoring can reverse effects.

RESULTS

The claim rate within a Statistical Area was inversely associated with disability duration. However, this reversed when Statistical Areas were nested by state/territory. Left-censoring resulted in an attenuation of the unnested association to non-significance, while the nested association remained significantly positive. Cox regressions with simulated claims data demonstrated how left-censoring can reverse effects.

CONCLUSIONS

Collider bias can seriously confound work disability research, particularly cross-jurisdictional comparisons. Work disability researchers must grapple with this challenge by using appropriate study designs and analytical approaches, and considering how it affects the interpretation of results.

Self-certification versus physician certification of sick leave for reducing sickness absence and associated costs

BACKGROUND

From the societal and employers' perspectives, sickness absence has a large economic impact. Internationally, there is variation in sickness certification practices. However, in most countries a physician's certificate of illness or reduced work ability is needed at some point of sickness absence. In many countries, there is a time period of varying length called the 'self-certification period' at the beginning of sickness absence. During that time a worker is not obliged to provide his or her employer a medical certificate and it is usually enough that the employee notifies his or her supervisor when taken ill. Self-certification can be introduced at organisational, regional, or national level.

OBJECTIVES

To evaluate the effects of introducing, abolishing, or changing the period of self-certification of sickness absence on: the total or average duration (number of sickness absence days) of short-term sickness absence periods; the frequency of short-term sickness absence periods; the associated costs (of sickness absence and (occupational) health care); and social climate, supervisor involvement, and workload or presenteeism (see Figure 1).

SEARCH METHODS

We conducted a systematic literature search to identify all potentially eligible published and unpublished studies. We adapted the search strategy developed for MEDLINE for use in the other electronic databases. We also searched for unpublished trials on ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform (WHO ICTRP). We used Google Scholar for exploratory searches.

SELECTION CRITERIA

We considered randomised controlled trials (RCTs), controlled before-after (CBA) studies, and interrupted time-series (ITS) studies for inclusion. We included studies carried out with individual employees or insured workers. We also included studies in which participants were addressed at the aggregate level of organisations, companies, municipalities, healthcare settings, or general populations. We included studies evaluating the effects of introducing, abolishing, or changing the period of self-certification of sickness absence.

DATA COLLECTION AND ANALYSIS

We conducted a systematic literature search up to 14 June 2018. We calculated missing data from other data reported by the authors. We intended to perform a random-effects meta-analysis, but the studies were too different to enable meta-analysis.

MAIN RESULTS

We screened 6091 records for inclusion. Five studies fulfilled our inclusion criteria: one is an RCT and four are CBA studies. One study from Sweden changed the period of self-certification in 1985 in two districts for all insured inhabitants. Three studies from Norway conducted between 2001 and 2014 changed the period of self-certification in municipalities for all or part of the workers. One study from 1969 introduced self-certification for all manual workers of an oil refinery in the UK.Longer compared to shorter self-certificationfor reducing sickness absence in workersOutcome: average duration of sickness absence periodsExtending the period of self-certification from one week to two weeks produced a higher mean duration of sickness absence periods: mean difference in change values between the intervention and control group (MD_change) was 0.67 days/period up to 29 days (95% confidence interval (95% CI) 0.55 to 0.79; 1 RCT; low-certainty evidence).The introduction of self-certification for a maximum of three days produced a lower mean duration of sickness absence up to three days (MD_change -0.32 days/period, 95% CI -0.39 to -0.25; 1 CBA study; very low-certainty evidence). The authors of a different study reported that prolonging self-certification from ≤ 3 days to ≤ 365 days did not lead to a change, but they did not provide numerical data (very low-certainty evidence).

OUTCOME

number of sickness absence periods per workerExtending the period of self-certification from one week to two weeks resulted in no difference in the number of sickness absence periods in one RCT, but the authors did not report numerical data (low-certainty evidence).The introduction of self-certification for a maximum of three days produced a higher mean number of sickness absence periods lasting up to three days (MD_change 0.48 periods, 95% CI 0.33 to 0.63) in one CBA study (very low-certainty evidence).Extending the period of self-certification from three days to up to a year decreased the number of periods in one CBA study, but the authors did not report data (very low-certainty evidence).

OUTCOME

average lost work time per 100 person-yearsExtending the period of self-certification from one week to two weeks resulted in an inferred increase in lost work time in one RCT (very low-certainty evidence).Extending the period of self-certification (introduction of self-certification for a maximum of three days (from zero to three days) and from three days to five days, respectively) resulted in more work time lost due to sickness absence periods lasting up to three days in two CBA studies that could not be pooled (MD_change 0.54 days/person-year, 95% CI 0.47 to 0.61; and MD_change 1.38 days/person-year, 95% CI 1.16 to 1.60; very low-certainty evidence).Extending the period of self-certification from three days up to 50 days led to 0.65 days less lost work time in one CBA study, based on absence periods lasting between four and 16 days. Extending the period of self-certification from three days up to 365 days resulted in less work time lost due to sickness absence periods longer than 16 days (MD_change -2.84 days, 95% CI -3.35 to -2.33; 1 CBA study; very low-certainty evidence).

OUTCOME

costs of sickness absence and physician certificationOne RCT reported that the higher costs of sickness absence benefits incurred by extending the period of self-certification far outweighed the possible reduction in costs of fewer physician appointments by almost six to one (low-certainty evidence).In summary, we found very low-certainty evidence that introducing self-certification of sickness absence or prolonging the self-certification period has inconsistent effects on the mean number of sickness absence days, the number of sickness absence periods, and on lost work time due to sickness absence periods.

AUTHORS' CONCLUSIONS

There is low- to very low-certainty evidence of inconsistent effects of changing the period of self-certification on the duration or frequency of short-term sickness absence periods or the amount of work time lost due to sickness absence. Because the evidence is of low or very low certainty, more and better studies are needed.