Sickness Certification Research Articles

Predicting return to work among sickness-certified patients in general practice: Properties of two assessment tools

Aim. The purpose was to analyse the properties of two models for the assessment of return to work after sickness certification, a manual one based on clinical judgement including non-measurable information (‘gut feeling’), and a computer-based one.Study population. All subjects aged 18 to 63 years, sickness-certified at a primary health care centre in Sweden during 8 months (n = 943), and followed up for 3 years.Methods. Baseline information included age, sex, occupational status, sickness certification diagnosis, full-time or part-time current sick-leave, and sick-leave days during the past year. Follow-up information included first and last day of each occurring sick spell. In the manual model all subjects were classified, based on baseline information and gut feeling, into a high-risk (n = 447) or a low-risk group (n = 496) regarding not returning to work when the present certificate expired. It was evaluated with a Cox’s analysis, including time and return to work as dependent variables and risk group assignment as the independent variable, while in the computer-based model the baseline variables were entered as independent variables.Results. Concordance between actual return to work and return to work predicted by the analysis model was 73%–76% during the first 28–180 days in the manual model, and approximately 10% units higher in the computer-based model. Based on the latter, three nomograms were constructed providing detailed information on the probability of return to work.Conclusion. The computer-based model had a higher precision and gave more detailed information than the manual model.

Extending the authority for sickness certification beyond the medical profession: the importance of 'boundary work'.

BackgroundThe study aimed to explore the views of general practitioners (GPs), nurses and physiotherapists towards extending the role of sickness certification beyond the medical profession in primary care.MethodsFifteen GPs, seven nurses and six physiotherapists were selected to achieve varied respondent characteristics including sex, geographical location, service duration and post-graduate specialist training. Constant-comparative qualitative analysis of data from 28 semi-structured telephone interviews was undertaken.ResultsThe majority of respondents supported the extended role concept; however members of each professional group also rejected the notion. Respondents employed four different legitimacy claims to justify their views and define their occupational boundaries in relation to sickness certification practice. Condition-specific legitimacy, the ability to adopt a holistic approach to sickness certification, system efficiency and control-related arguments were used to different degrees by each occupation. Practical suggestions for the extension of the sickness certification role beyond the medical profession are underpinned by the sociological theory of professional identity.ConclusionsExtending the authority to certify sickness absence beyond the medical profession is not simply a matter of addressing practical and organisational obstacles. There is also a need to consider the impact on, and preferences of, the specific occupations and their respective boundary claims. This paper explores the implications of extending the sick certification role beyond general practice. We conclude that the main policy challenge of such a move is to a) persuade GPs to relinquish this role (or to share it with other professions), and b) to understand the ‘boundary work’ involved.

Effect of Stratified Care for Low Back Pain in Family Practice (IMPaCT Back): A Prospective Population-Based Sequential Comparison

We aimed to determine the effects of implementing risk-stratified care for low back pain in family practice on physician's clinical behavior, patient outcomes, and costs. The IMPaCT Back Study (IMplementation to improve Patient Care through Targeted treatment) prospectively compared separate patient cohorts in a preintervention phase (6 months of usual care) and a postintervention phase (12 months of stratified care) in family practice, involving 64 family physicians and linked physical therapy services. A total of 1,647 adults with low back pain were invited to participate. Stratified care entailed use of a risk stratification tool to classify patients into groups at low, medium, or high risk for persistent disability and provision of risk-matched treatment. The primary outcome was 6-month change in disability as assessed with the Roland-Morris Disability Questionnaire. Process outcomes captured physician behavior change in risk-appropriate referral to physical therapy, diagnostic tests, medication prescriptions, and sickness certifications. A cost-utility analysis estimated incremental quality-adjusted life-years and back-related health care costs. Analysis was by intention to treat. The 922 patients studied (368 in the preintervention phase and 554 in the postintervention phase) had comparable baseline characteristics. At 6 months follow-up, stratified care had a small but significant benefit relative to usual care as seen from a mean difference in Roland-Morris Disability Questionnaire scores of 0.7 (95% CI, 0.1-1.4), with a large, clinically important difference in the high risk group of 2.3 (95% CI, 0.8-3.9). Mean time off work was 50% shorter (4 vs 8 days, P = .03) and the proportion of patients given sickness certifications was 30% lower (9% vs 15%, P = .03) in the postintervention cohort. Health care cost savings were also observed. Stratified care for back pain implemented in family practice leads to significant improvements in patient disability outcomes and a halving in time off work, without increasing health care costs. Wider implementation is recommended.

Tussles and Rollovers: Negotiating Sickness Certification in Primary Care

Sickness certification in primary care is increasingly the focus of new policies, practices and politics which are associated with keeping people in work rather than moving on to sickness absence. However, there are considerable tensions for practitioners from their role in sickness certification. The decision to issue a sicknote is influenced by a number of factors including the needs of their patient, their own attitudes towards work, and their responsibility to the state or employer. Some patients, such as those with Medically Unexplained Symptoms (MUS), are particularly challenging for Practitioners, as they do not fit the “sick role” and are difficult to negotiate with. We present the first taxonomy from actual sicknote consultations between General Medical Practitioners (GPs) and their patients, classifying the types of requests and the associated responses. Although, most sicknote requests do result in a sicknote, GPs do gather information about the patient’s social, occupational, and family circumstances, negotiate absences from work, impose terms and conditions upon the patient, and challenge patients’ illness constructions. Our findings suggest that, despite the tensions for GPs in managing these patients, sicknote consultations can be an important juncture for the clinicians and patients, particularly in light of the move from an illness deficit model towards a health capacity model, where work is considered health-giving, and not a barrier to illness recovery. This resonates with the switch in the UK to a “fitnote” approach from the previous “sicknote” one.

Trends in Sickness Certification of Injured Workers by General Practitioners in Victoria, Australia

General practitioners (GPs) play a critical role in facilitating injured workers return to work via their ability to certify capacity to return to employment. However, little is known about the sickness certification patterns of GPs in the context of workers' compensation claims. To determine if GPs' sickness certification behaviour has changed between 2003 and 2010 in Victoria, Australia. Retrospective population-based cohort study of all injured workers with an accepted compensation claim. Sickness certification rates per 1,000 working population per annum were calculated. General regression models adjusted for workers' age and annual claim number were fitted to summarize changes in count and duration (expressed as incidence rate ratios or IRRs) of unfit for work (UFW) versus alternate duties (ALT) certificates within six categories of work-related injury and disease. 92,134 UFW and 28,293 ALT certificates were identified. A significant decrease in the unadjusted annual certification rates per 1,000 working population was observed. However, after adjusting for the annual number of claims and age, the IRRs of certificates increased over time. The rate of injuries and IRRs of certificates varied across affliction categories, IRRs being higher in mental health conditions in women than in men (IRR: 0.40, 95 % CI 0.38-0.41 vs. IRR: 0.17, 95 % CI 0.16-0.18). The duration of certificates remained stable, with the ALT being longer than UFW certificates in all claimants. Our findings indicate that GPs in Victoria issue an increasing number of UFW sickness certificates each year. Further research is required to investigate the reasons for such practises.

Are all-cause and diagnosis-specific sickness absence, and sick-leave duration risk indicators for suicidal behaviour? A nationwide register-based cohort study of 4.9 million inhabitants of Sweden

ObjectivesRecent studies have found an increased risk of suicide in people on sickness absence, but less is known about to what extent diagnosis-specific sickness absence is a risk indicator for...

Occupational physicians have better prerequisites for handling sickness certification cases, compared to other physicians - results from a nation-wide survey in Sweden

Background Physicians have been shown to experience handling of sickness certification as problematic. Physicians working in occupational health service (occupational physicians, OPs), have been proposed as better suited for handling sickness certification, compared to e.g. general practitioners. This study aimed at gaining knowledge on what signified OPs’ work with sickness certification compared to that of other physicians, and to test the association of OPs experience of assessment of patients’ work capacity with some potentially …

Sickness certification of workers compensation claimants by general practitioners in Victoria, 2003–2010

To examine patterns of the sickness certification of workers compensation claimants by general practitioners in Victoria, Australia, by nature of injury or illness. Retrospective analysis of Victorian workers compensation data for all injured and ill workers with an accepted workers compensation claim between 2003 and 2010. Type (unfit for work, alternative duties, or fit for work) and duration of initial medical certificates relating to workers compensation claims that were issued by GPs, in six categories of injury and illness. Of 124,424 initial medical certificates issued by GPs, 74.1% recommended that workers were unfit for work and 22.8% recommended alternative duties. Unfit-for-work certificates were issued to 94.1% of workers with mental health conditions, 81.3% of those with fractures, 79.1% of those with other traumatic injuries, 77.6% of those with back pain and strains, 68.0% of those with musculoskeletal conditions and 53.0% of those with other diseases. Alternative-duties certificates were significantly longer in duration than unfit-for-work certificates in all injury and illness categories (P < 0.001) but certificates for workers with musculoskeletal injuries and diseases, back pain and strains and other traumatic injuries were of lesser duration than those for workers with fractures, mental health conditions and other diseases. The high proportion of medical certificates recommending complete absence from work presents major challenges in terms of return to work, labour force productivity, the viability of the compensation system, and long-term social and economic development. There is substantial variation in the type and duration of medical certificates issued by GPs. People with mental health conditions are unlikely to receive a certificate recommending alternative duties. Further research is required to understand GP certification behaviour.

Sickness certificates: what information do they provide about rehabilitation?

Purpose: To investigate whether patients are prescribed rehabilitation early in a new sick leave period, and whether this prescription is associated with sex, age, diagnosis, description of functioning and affiliation of certifying physician. Method: A cross-sectional study using data from sickness certificates issued during a total sick leave period, collected consecutively during 2 weeks in 2007 in Östergötland County, Sweden. Rehabilitation prescribed in the first certificate or within 28 days after the start of sick leave was defined as early rehabilitation. Results: Musculoskeletal diseases (MSD) were the largest diagnostic group, followed by mental disorders (MD). The mean duration of sick leave was 94 days (SD 139), longest for MD patients. Early rehabilitation was prescribed in 27% of all certificates and in 45% of certificates for MSD and MD diagnoses. Logistic regression analysis indicated that prescription of early rehabilitation was associated with certificates issued for MSD and MD, youngest patients, and certificates issued by primary health care physicians. The final model explained 29% of variation in the prescription of early rehabilitation. Conclusions: There is a modest prescription of early rehabilitation in sickness certificates, based on younger age and MSD or MD diagnosis. This indicates that patients’ rehabilitation needs may not have been identified.Implications for RehabilitationSickness certificates are the decision basis for entitlement to sickness benefits and return to work (RTW) measures conveyed between the health care, the social insurance office and employers.Sickness certificates were found to provide modest information about early rehabilitation and RTW measures, indicating that patients’ rehabilitation needs may not have been identified.As a communication tool, this scarce information might have implications for the patient regarding RTW measures or work modifications.

Return to work with chronic pain: employers' and employees' views

The sickness certification and return to work (RTW) of people with chronic pain are important health and economic issues for employees, employers, taxpayers and the UK government. The 'fit note' and a national educational programme promoting RTW were introduced in 2010 to curb rising rates of sickness absence. To investigate employers' and employees' experiences of managing RTW when someone has taken sick leave for chronic pain and to explore the perceived efficacy of the fit note. A qualitative study, comprising semi-structured interviews with employers who had managed sick leave cases and employees who had experienced sick leave for chronic pain. Interviews were recorded, transcribed and the data analysed using constructivist grounded theory principles. Five themes were elicited. Firstly, frequent enquiry after health status was seen as intrusive by some employees but part of good practice by employers and acknowledging this difference was useful. Secondly, being able to trust employees due to their performance track record was helpful for employers when dealing with complex chronic pain conditions. Thirdly, feeling valued increased employees' motivation to RTW. Fourthly, guidelines about maintaining contact with absent employees were useful if used flexibly. Finally, both parties valued the fit note for its positive language, interrogative format and biomedical authority. The fit note was perceived to be helpful if used in combination with other strategies for managing sick leave and RTW for people with chronic pain. These strategies may be applicable to other fluctuating, long-term conditions with medically unexplained elements.

Early multidisciplinary assessment was associated with longer periods of sick leave: A randomized controlled trial in a primary health care centre

Objective. To study the effects on sick leave from an early multidisciplinary assessment at a primary health care centre. Design. Randomized controlled trial. Setting. Patients who saw GPs at a primary health care centre in mid-Sweden and asked for a sickness certificate for psychiatric or musculoskeletal diagnoses were invited to participate. Patients included were sick-listed for less than four weeks; 33 patients were randomized either to an assessment within a week by a physiotherapist, a psychotherapist, and an occupational therapist or to “standard care”. The therapists used methods and tools they normally use in their clinical work. Main outcome measure. Proportion of patients still sick-listed three months after randomization, total and net days on sick leave, and proportion who were on part-time sick leave. Results. At follow-up after three months, in contrast to the pre-trial hypothesis, there was a trend toward a higher proportion of patients still sick-listed in the intervention group (7/18) as compared with the control group (3/15). The intervention group also had significantly longer sick-listing periods (mean 58 days) than the control group (mean 36 days) (p = 0.038). The proportion of patients who were part time sick-listed was significantly higher in the intervention group (10/18) than in the control group (2/15) (p = 0.027). Conclusions. In this study an early multidisciplinary assessment was associated with longer periods on sick leave and more individuals on part-time sick leave.

Sickness certification at oncology clinics: perceived problems, support, need for education and reasons for certifying unnecessarily long sickness absences

Physicians' work with sickness certifications is an understudied field. The aims of this study were to gain knowledge of experiences concerning the sickness certification process among physicians working at oncology clinics. In 2008, all physicians working in Sweden (n = 36 898) were sent a questionnaire concerning sick-listing practices. All respondents working at an oncology clinic (n = 428) were included in the current study. Most of the physicians had sickness certification consultations at least weekly (91.3%). More than one fifth (22.3%) reported that they worked at a clinic with a workplace policy regarding the handling of sickness certification and 61.1% reported receiving at least some support in such cases from their immediate manager. Issuing unnecessary long sickness certificates were related to experiencing delicate interactions with patients and to lack of time. To a moderate degree, further competence was requested regarding: different types of compensation in the social insurance system, responsibilities of the Social Insurance Agency and employers, and sickness insurance rules. The large majority of physicians working in oncology reported regularly having consultations involving sickness certification. Overall, they reported few problems, low level of need for more competence regarding sickness certification, and low frequency of issuing sickness absences for longer periods than necessary.

Problems experienced by gynecologists/obstetricians in sickness certification consultations

To explore frequencies and experiences with problems in sickness certification consultations among gynecologists and obstetricians in two different years. Cross-sectional surveys on two occasions; in 2004 and 2008. Gynecological, obstetric and maternal health care. Physicians working in gynecology, obstetrics or maternal health care in two Swedish counties from two samples: in 2004 (n = 315), and in 2008 (n = 327). Data regarding sickness certification consultations were obtained from comprehensive questionnaires that had been mailed to the physicians in two Swedish counties in 2004 and in 2008, respectively. Frequencies and types of problems in sickness certification consultations, organizational support, and need to acquire more competence. The majority experienced that patients requested to be on sick leave for a reason other than work incapacity due to disease or injury, at least a few times per year (85% in 2004 and 88% in 2008). The most problematic situation to handle was when the physician and the patient had different opinions about the need for sick leave (2004: 66% and 2008: 58%). The physicians expressed a need for more competence about the options and responsibilities of employers, social insurance officers and physicians in sickness certification cases. Most gynecologists/obstetricians find sickness certification consultations problematic and especially when encountering patients requesting to be on sick leave for reasons other than disease. The physicians expressed a need for more competence in insurance medicine, especially about their own and other stakeholders' options and responsibilities.

Sickness certification difficulties in Ireland--a GP focus group study

Sickness certification causes problems for general practitioners (GPs). Difficulty with the assessment of capacity to work, conflict with patients and other non-medical factors have been shown to influence GPs' decision-making. Inadequate leadership and management of certification issues add to GPs' difficulties. To explore problems associated with sickness certification, as part of a larger mixed method research project exploring GPs' experiences and perceptions of sickness certification in Ireland. A qualitative study in an urban region of Ireland. A focus group of four male and four female GPs explored problems encountered by GPs in certifying sickness absence. Thematic data analysis was used. Three major themes emerged: perception of the sickness certification system, organization of health care and cultural factors in sickness absence behaviour. Employment structures in public and private sectors and lack of communication with other health care providers and employers were identified as complicating sickness certification. GPs encounter a complexity of issues in sick certification and are dissatisfied with their role in certifying sickness absence. Our results open the debate for policy change and development in Ireland.

Health care management of sickness certification tasks: results from two surveys to physicians

BackgroundHealth care in general and physicians in particular, play an important role in patients’ sickness certification processes. However, a lack of management within health care regarding how sickness certification is carried out has been identified in Sweden. A variety of interventions to increase the quality of sickness certification were introduced by the government and County Councils. Some of these measures were specifically aimed at strengthening health care management of sickness certification; e.g. policy making and management support. The aim was to describe to what extent physicians in different medical specialties had access to a joint policy regarding sickness certification in their clinical settings and experienced management support in carrying out sickness certification.MethodA descriptive study, based on data from two cross-sectional questionnaires sent to all physicians in the Stockholm County regarding their sickness certification practice. Criteria for inclusion in this study were working in a clinical setting, being a board-certified specialist, <65 years of age, and having sickness certification consultations at least a few times a year. These criteria were met by 2497 physicians in 2004 and 2204 physicians in 2008. Proportions were calculated regarding access to policy and management support, stratified according to medical specialty.ResultsThe proportions of physicians working in clinical settings with a well-established policy regarding sickness certification were generally low both in 2004 and 2008, but varied greatly between different types of medical specialties (from 6.1% to 46.9%). Also, reports of access to substantial management support regarding sickness certification varied greatly between medical specialties (from 10.5% to 48.8%). More than one third of the physicians reported having no such management support.ConclusionsMost physicians did not work in a clinical setting with a well-established policy on sickness certification tasks, nor did they experience substantial support from their manager. The results indicate a need of strengthening health care management of sickness certification tasks in order to better support physicians in these tasks.

Reasons for and factors associated with issuing sickness certificates for longer periods than necessary: results from a nationwide survey of physicians

BackgroundPhysicians’ work with sickness certifications is an understudied field. Physicians’ experience of sickness certifying for longer periods than necessary has been previous reported. However, the extent and frequency of such sickness certification is largely unknown. The aims of this study were: a) to explore the frequency of sickness certifying for longer periods than necessary among physicians working in different clinical settings; b) to examine main reasons for issuing sickness certificates for longer periods than necessary; and c) to examine factors associated with unnecessary issued sickness certificates.MethodsIn 2008, all physicians living and working in Sweden (a total of 36,898) were sent an invitation to participate in a questionnaire study concerning their sick-listing practices. A total of 22,349 (60.6%) returned the questionnaire. In the current study, physicians reporting handling sickness certification consultations at least weekly were included in the analyses, a total of 12,348.ResultsThe proportion of physicians reporting issuing sickness certificates for longer periods than actually necessary varied greatly between different types of clinics, with the highest frequency among those working at: occupational medicine, orthopedic, primary health care, and psychiatry clinics; and lowest among those working in: eye, dermatology, ear/nose/throat, oncology, surgery, and infection clinics. Logistic analyses showed that sickness certifying for longer periods than necessary due to limitations in the health care system was particularly common among physicians working at occupational medicine, orthopedic, and primary health care clinics. Sickness certifying for longer periods than necessary due to patient-related factors was much more common among physicians working at psychiatric clinics. In addition to differences between clinics, frequency of sickness certificates issued for longer periods than necessary varied by age, physicians’ experiences of different situations, and perceived problems.ConclusionsThis study showed that physicians issued sickness certificates for longer periods than actually necessary quite frequently at some types of clinics. Differences between clinics were to a large extent associated with frequency of problems, lack of time, delicate interactions with patients, and need for more competence.

Quality of sickness certification in primary health care: a retrospective database study

BackgroundIn the period 2004–2009, national and regional initiatives were developed in Sweden to improve the quality of sickness certificates. Parameters for assessing the quality of sickness certificates in primary health care have been proposed. The aim of this study was to measure the quality of sickness certification in primary health care by means of assessing sickness certificates issued between 2004 and 2009 in Stockholm.MethodsThis was a retrospective study using data retrieved from sickness certificates contained in the electronic patient records of 21 primary health care centres in Stockholm County covering six consecutive years. A total number of 236 441 certificates were used in the current study. Seven quality parameters were chosen as outcome measures. Descriptive statistics and regression models with time, sex and age group as explanatory variables were used.ResultsDuring the study period, the quality of the sickness certification practice improved as the number of days on first certification decreased and the proportion of duly completely and acceptable certificates increased. Assessment of need for vocational rehabilitation and giving a prognosis for return to work were not significantly improved during the same period. Time was the most influential variable.ConclusionsThe quality of sickness certification practice improved for most of the parameters, although additional efforts to improve the quality of sickness certificates are needed. Measures, such as reminders, compulsory certificate fields and structured guidance, could be useful tools to achieve this objective.

Certifying fitness to work

Around 131 million days of work were lost to sickness in the UK in 2011, an average of 4.5 days per worker. Although there has been a decrease in sickness absence in the UK over recent years, there is still a perception that illness is incompatible with work. Conversely, a substantial body of evidence suggests that earlier return to work results in better outcomes. One of the many roles of GPs is to act as gatekeepers to sickness-related benefits through the issuing of certificates confirming incapacity to work or ‘sick notes’. With this comes a responsibility to enable and assist patients to return to work at the earliest possibility. However, many GPs have received little or no training in sickness certification and occupational health and find this a difficult area of practice fraught with perceived conflicts and ethical dilemmas. This article outlines the evidence in support of early return to work and overviews the sickness certification system in the UK, providing signposts for GPs to make their task easier.

Primary Healthcare Professionals’ Experiences of the Sick Leave Process: A Focus Group Study in Sweden

The aim of this study was to explore primary healthcare (PHC) professionals' experiences of the sick leave process. This is an explorative study using data from four semi-structured focus group discussions with a purposeful sample of PHC professionals in Östergötland County, Sweden. Content analysis with an inductive approach was used in the analysis. Four key themes emerged from the analysis; priority to the sick leave process, handling sickness certifications, collaboration within PHC and with other stakeholders, and work ability assessments. Patients' need for sick leave was handled from each professional group's perspective. Collaboration was considered important, but difficult to achieve and all the competencies available at the PHC centre were not used for work ability assessments. There was insufficient knowledge of patients' work demands and contact with an employer was rare, and the strained relationship with the social insurance officers affected the collaboration. This study highlights the challenges physicians and other PHC professionals face when handling the need for sick leave, especially when encountering patients with symptom-based diagnoses, and the influence of non-medical factors. Hindrances to good practice were increased demands, collaboration, and role responsibility. The challenges in the sick leave process concerned both content and consequences related to poor collaboration within PHC and with representatives from various organizations, primarily employers and social insurance officers. Further research on how to develop a professional approach for handling the sick leave process is needed.

A population based validation study of self-reported pensions and benefits: the Nord-Trøndelag health study (HUNT)

BackgroundMeasures of disability pensions, sickness certification and long-term health related benefits are often self-reported in epidemiological studies. Few studies have examined these measures, and the validity is yet to be established.We aimed to estimate the validity of self-reported disability pension, rehabilitation benefit and retirement pension and to explore the benefit status and basic characteristics of those not responding to these items.A large health survey (HUNT2) containing self-reported questionnaire data on sickness benefits and pensions was linked to a national registry of pensions and benefits, used as “gold standard” for the analysis. We investigated two main sources of bias in self-reported data; misclassification - due to participants answering questions incorrectly, and systematic missing/selection bias - when participants do not respond to the questions.Sensitivity, specificity, positive (PPV) and negative (NPV) predicative value, agreement and Cohen’s Kappa were calculated for each benefit. Co-variables were compared between non-responders and responders.ResultsIn the study-population of 40,633, 9.2% reported receiving disability pension, 1.4% rehabilitation benefits and 6.1% retirement pension. According to the registry, the corresponding numbers were 9.0%, 1.7% and 5.4%. Excluding non-responders, specificity, NPV and agreement were above 98% for all benefits. Sensitivity and PPV were lower. When including non-responders as non-receivers, specificity got higher, sensitivity dropped while the other measures changed less.Between 17.7% and 24.1% did not answer the questions on benefits. Non-responders were older and more likely to be female. They reported more anxiety, more depression, a higher number of somatic diagnoses, less physical activity and lower consumption of alcohol (p < 0.001 for all variables). For disability pension and retirement pension, non-responders were less likely to receive benefits than responders (p < 0.001). For each benefit 2.1% or less of non-responders were receivers. False positive responses were more prevalent than false negative responses.ConclusionsThe validity of self-reported data on disability pension, rehabilitation benefits and retirement pension is high – it seems that participants’ responses can be trusted. Compared to responders, non-responders are less likely to be receivers. If necessary, power and validity can be kept high by imputing non-responders as non-receivers.