Design of the DIRECT-project: interventions to increase job resources and recovery opportunities to improve job-related health, well-being, and performance outcomes in nursing homes
© Spoor et al; licensee BioMed Central Ltd. 2010
Received: 29 April 2010
Accepted: 28 May 2010
Published: 28 May 2010
Because of high demands at work, nurses are at high risk for occupational burnout and physical complaints. The presence of job resources (such as job autonomy or social support) and recovery opportunities could counteract the adverse effect of high job demands. However, it is still unclear how job resources and recovery opportunities can be translated into effective workplace interventions aiming to improve employee health, well-being, and performance-related outcomes. The aim of the current research project is developing and implementing interventions to optimize job resources and recovery opportunities, which may lead to improved health, well-being and performance of nurses.
The DIRECT-project (DIsc Risk Evaluating Controlled Trial) is a longitudinal, quasi-experimental field study. Nursing home staff of 4 intervention wards and 4 comparison wards will be involved. Based on the results of a base-line survey, interventions will be implemented to optimize job resources and recovery opportunities. After 12 and 24 month the effect of the interventions will be investigated with follow-up surveys. Additionally, a process evaluation will be conducted to map factors that either stimulated or hindered successful implementation as well as the effectiveness of the interventions.
The DIRECT-project fulfils a strong need for intervention research in the field of work, stress, performance, and health. The results could reveal (1) how interventions can be tailored to optimize job resources and recovery opportunities, in order to counteract job demands, and (2) what the effects of these interventions will be on health, well-being, and performance of nursing staff.
Nurses are at high risk for occupational burnout [1–3] and physical complaints, merely due to high demands at work [4, 5]. Because job demands often cannot be easily reduced, it is rather appealing to counteract the adverse effects of high job demands on well-being and health with so-called job resources . Job resources can be broadly conceptualized as different kinds of energey reservoirs that can be tapped when the employee has to cope with job demands [7, 8]. Examples of job resources are job autonomy, colleagues providing help, sympathy, and affection, and ergonomic aids. Empirical research has shown that job resources are important stress buffers for nurses . In addition, Taris et al.  showed that a well-balanced mix of job demands and job resources is positive related to well-being, and that well-being is positive related to performance indicators such as client satisfaction and efficiency.
Besides the availability of job resources to counteract high job demands, recovery from job demands can also be an important prerequisite for not feeling strained and for performing well when returning to work the next day. According to Meijman and Mulder , recovery occurs when no further demands are put on those aspects of an individual's functioning on which job demands have been put during the work process. There is empirical evidence showing that recovery from work is positively related to employees' health and well-being [12–15], as well as to job performance .
Because job demands can often not be reduced, organizations need to implement workplace interventions that revolve around the management of job resources and recovery opportunities. However, there is a gap between theoretical knowledge gained from work stress and performance models and their practical implications . According to Kompier and Taris , there is a strong need for intervention research in the field of work, stress, performance, and health. The current research project fills-in this gap by developing and implementing interventions to optimize job resources and recovery opportunities. This may lead to improved health and performance of nurses. Because a systematic analysis of risk factors is often lacking in stress intervention research , a strength of the present study is the adequate diagnosis of risk factors conform a recent developed theoretical model called the Demand-Induced Strain Compensation (DISC) Model [6, 20]. This is in line with Goldenhar et al. , who called for theory-driven intervention research to learn why and under what circumstances work-oriented interventions succeed.
In more detail, the DISC Model treats job demands and job resources as multidimensional constructs. In line with Hockey , three type of job demands can be distinguished: (1) cognitive demands which primarily impinge on the brain processes involved in information processing , (2) emotional demands which primarily refer to the effort needed to deal with organizationally desired emotions during interpersonal transactions , and (3) physical demands which are primarily associated with the musculo-skeletal system . Similarly, job resources may encompass a cognitive component (e.g. access to useful information from books), an emotional component (e.g. colleagues providing sympathy and affection), and a physical component (e.g. ergonomic aids). Finally, in line with Sonnentag and Niessen , recovery from work can also be divided in a cognitive component (think on other things than work), an emotional component (put all emotions from work aside), and a physical component (i.e. not longer affected by the work posture). Based upon homeostatic functional self-regulation processes, the DISC Model proposes that job resources as well as recovery within the same domain as the job demands (i.e. cognitive, emotional, or physical) will produce a greater likelihood of counteracting the negative job demands and creates optimal conditions for health, well-being, and performance . For example, high emotional job demands (e.g. dealing with dying patients) can lead to emotional exhaustion, unless employees have high emotional resources (e.g. social support from colleagues) and a high level of emotional recovery (e.g. meeting with friends after work) to counteract the high emotional demands.
Aim and research question
The aim of the current study is developing, implementing, and evaluating interventions to optimize job resources and recovery opportunities, which may lead to improved health, well-being and performance of nurses. The interventions that will be implemented after a baseline measure, will be based on the central principle of the DISC Model, i.e. the amount of specific job resources and recovery opportunities have to match with the corresponding types of job demands to optimize job-related outcomes. These interventions will be primarily work-oriented, i.e. changing the work situation rather than changing the employee or his/her perceptions. A meta-analysis of stress management interventions  showed that only a few studies assessed the impact of work-oriented interventions, and that there is a paucity of research which compared different kinds of interventions on respective, similar, outcomes. The research question is: Does a tailored intervention program based upon the DISC Model result in an improvement of employee health, well-being and performance-related outcomes? In other words, how can job demands, job resources, and recovery both during and after work time be optimized to improve health, well-being and performance of nursing staff?
Methods and design
All nursing staff (i.e. nursing assistants, certified nursing assistants, and registered nurses) working on a permanent basis at one of the eight wards, will be eligible to participate in the study. Because of the longitudinal character of the project, temporary staff will be excluded.
The measures that will be used in both the baseline survey and the follow-up surveys are described below.
Cognitive, emotional and physical job demands and job resources will be measured with a well-validated version of the DISC Questionnaire (DISQ), which was particularly developed for testing this theoretical model [9, 29]. Cognitive job demands primarily impinge on brain processes involved in information processing, e.g., "Employee X will need to display high levels of concentration and precision at work". Emotional job demands can be defined as the effort needed to deal with job inherent emotions and/or organizationally desired emotions during interpersonal transactions, e.g., "Employee X will have to display emotions (e.g., towards clients, colleagues or supervisors) that are inconsistent with his/her current feelings". Physical job demands refer to static and dynamic physical exertion at work, e.g., "Employee X will have to lift or move heavy persons or objects (more than 10 kg)". Cognitive job resources refer to the opportunity to determine a variety of task aspects and to use problem solving skills, e.g., "Employee X would have the opportunity to take a break when tasks require a lot of concentration". To improve the internal reliability of the scale, one item was added to the original questionnaire ("Employee X will have the opportunity to determine their own work method"). Emotional job resources refer to emotional support from colleagues or supervisors, e.g., "Other people (e.g., clients, colleagues or supervisors) would be a listening ear for employee X when he/she has faced a threatening situation". Finally, physical job resources refer to instrumental support from colleagues and supervisors, or ergonomic aids at work, e.g., "Employee X would receive help from others (e.g., clients, colleagues or supervisors) in lifting or moving heavy persons or objects". All but two scales consist of five items (except for emotional demands and cognitive resources: six items) that can be scored on a 5-point frequency scale, ranging from 1 (never or very rarely) to 5 (very often or always) Recovery from work. Recovery refers to an employee's sense of being away from the work situation. It will be measured with a scale developed by De Jonge et. al. ("Take a break?" Off-job recovery, job demands and job resources as predictors of active learning, creativity, and health, submitted) and may encompass a cognitive, emotional and physical component. Each component will be measured with three items. Example items are: "After work, I put all thoughts of work aside" (cognitive), "After work, I emotionally distance myself from work" (emotional), "After work, I shake off the physical exertion from work" (physical). The items can be scored on a 5-point frequency scale, ranging from 1 (never) to 5 (always).
Concentration problems will be measured with three items derived from a semantic differential scale developed by Meijman . The 5-point response scale have two extremes, for example 'No concentrating difficulties' and 'Concentration difficulties'. Emotional exhaustion will be measured by the well-validated Dutch version  of the Maslach Burnout Inventory . The scale contained five items with a 7-point response scale ranging from 0 (never) to 6 (always, daily). An example item is: "I feel emotionally drained from my work".
Physical complaints refer to neck, shoulder and back problems in the last six months and will be measured with three items derived from a scale developed by Hildebrandt and Douwes . The possible responses are 1 (no), 2 (sometimes), and 3 (yes).
Job satisfaction & Work motivation will be measured by scales developed by De Jonge . Job satisfaction can be considered as a unidimensional and general construct, resulting from positive and negative work experiences. It will me measured with one item i.e. "I am satisfied with my present job". Work motivation is the extent to which the work is stimulating, interesting, and challenging and will be measured with five items. For example, "My work is very interesting". All items are measured on a 5-point Likert scale, ranging from 1 (strongly disagree) to 5 (strongly agree).
Active learning refers to the degree employees are enabled and stimulated to acquire new knowledge and skills, and to solve problems at their job. This scale  consists of four items that can be scored on a 4-point frequency scale, ranging from 1 ((almost) never) to 4 ((nearly) always). For example, "At work, I am challenged by new problems".
Employee creativity can be defined as the generation of novel and useful ideas by employees. This work-related construct will be assessed by a 7-item scale originally developed by George and Zhou , and translated/back-translated in a well-validated Dutch version . The scale can be scored on a 5-point rating scale ranging from 1 (never) to 5 (always). For example "Comes up with new and practical ideas to improve performance".
Development of workplace interventions
Evaluating the effects of workplace interventions
It is impossible to control all external influences on performance, well-being and health from the implementation of the interventions until the follow-up measures. However, some actions will be taken to get insight into factors that possibly affect the results. Therefore, a process evaluation will be carried out . The aim of this evaluation is to map factors that either stimulated or hindered successful implementation as well as the effectiveness of the interventions. The managers of the involved wards will be asked to note important changes and events on their wards in a logbook. Both after the first follow-up survey an the second follow-up survey, in-depth interviews will be held with the managers and nursing staff of both the intervention and comparison wards to interpret possibly changes in performance, well-being, and health on their ward. It will also be checked if employees on the intervention wards really perceived interventions. At the last page of both the follow-up surveys, they will be asked to list actions (since the previous survey) that were taken to improve health, well-being and performance on their ward. The same will be done with employees of the comparison wards. Consequently, it can be checked if managers of the comparison wards implemented interventions on their own initiative. In general, we will follow the intervention evaluation criteria as depicted by Scharf et al.  as much as possible.
At the base-line measure, each survey will be provided with a random chosen identification number corresponding to the employee. This number will be retained and used for the follow-up measures. The identification number is only available for the researchers and will be only used for analysis purposes. After completing, the employees can return the survey to the central researcher with a return envelope.
Sample size calculation
Sample size calculation is based on emotional exhaustion, measured by the Dutch version  of the Maslach Burnout Inventory . This measure is chosen because of the availability of norm scores for (certified) nursing assistant, which is the most occurring grade on both the intervention and comparison wards. The score ranges between 1 and 7, with an average score of M = 1.74 and a standard deviation of SD = 94. Setting alpha at 0.05, beta as 0.10 and Δ = .47 (half a standard deviation as a clinically minimal relevant difference  results in a required N = 120 (N = 60 for the experimental group and N = 60 for the comparison group) . However, eight wards (N = 300) were interested to participate in the research project. Taking drop-outs into account, this sample is expected to be large enough to detect significant effects.
Drop-outs will be documented thoroughly and included in the data-analysis to the point of drop-out. Analysis according to the guidelines by Goodman and Blum  will be conducted to assess any attrition effects. For instance, mean differences on measures from the base-line survey between those who responded and did not respond to the follow-up surveys.
Cross-sectional, baseline, relations between specific types of job demands, job resources, recovery and job-related outcomes will be tested with hierarchical regression analysis (SPSS for Windows) and structural equation modeling (LISREL for Windows). In order to analyze causal associations within the two different waves, structural equation modeling (LISREL for Windows) will be used, as this technique is more useful to 'prove' causation (i.e. to rule out alternative, causal, assumptions). To evaluate the results of the interventions after the follow-up measures, multilevel repeated measures analysis will be performed using MLwiN. This technique has several advantages compared to repeated measures MANOVA, like the inclusion of cases with incomplete data and less restrictive missing data assumptions.
Given the non-intrusive nature of the research, ethical approval seems to be not required. Nevertheless, we submitted the research proposal to the Medical Ethics Committee of the azM and Maastricht University, and she gave a positive advise. In addition, the research plan was presented to the union boards of the participating nursing homes and they gave their consent as well. Employees participate in the research project on a voluntary basis and confidentiality is guaranteed.
Although the literature showed that the availability of sufficient job resources and recovery opportunities have a positive influence on several job related outcomes, it is still unclear how job resources and recovery opportunities can be translated into effective workplace interventions aiming to improve employee health, well-being, and performance-related outcomes. The current research project will overcome this deadlock in research. It will be investigated how workplace interventions can be tailored to optimize job resources and recovery opportunities, in order to counteract job demands, and what the effects of these interventions will be on health, well-being, and performance of nursing home employees.
According to Kompier and Kristensen , a systematic analysis of risk factors is often lacking in stress intervention research. Hence, a strength of the present study is the adequate diagnosis of risk factors conform the principles of the Demand-Induced Strain Compensation (DISC) Model [6, 20]. Because only a few studies assessed the impact of work-oriented interventions , investigating the effects of these interventions on health, well-being, and performance is a second strength of the current study. A third strength of the research project is the use of a Participatory Action Research (PAR) approach , through which the commitment of employees during the process of developing and implementing interventions will be stimulated. A final strength of this study is the comparison of different interventions on respective, similar, outcomes. According to Richardson and Rothstein , this is an important contribution to both theory and practice.
Besides the obvious strengths of the present study, there are also some limitations. First, the design of the study is not a true experimental design. The wards participating in the present research project are existing organization units. Due to ethical and practical drawbacks, randomization is difficult to realize. However, the experimental- and comparison wards were selected in pairs so each intervention department has a similar comparison department. According to Ovretweit  'Traditional experimental evaluation design is not well suited to investigating social systems or the complex way in which interventions work with subjects or her environment' (p99). Secondly, It is impossible to control all external influences on performance, well-being and health from the implementation of the interventions until the follow-up measures. To overcome this problem a thoroughly process evaluation will be conducted to detect and interpret external influences.
Although the limitations, the design of the present study is a feasible method to assess the effect of optimizing job demands, job resources, and recovery on health, well-being and performance related outcomes. The study is in progress. The baseline paper-and-pencil survey was conducted in the Spring of 2009. Interventions will be developed and scheduled to be implemented within due course. Follow up measurements are planned in 2010 and 2011, respectively. Dissemination of results is planned for the end of 2011.
This study is funded by the Eindhoven University of Technology, De Zorgcirkel, and MeanderGroep Zuid-Limburg.
- Piko BF: Burnout, role conflict, job satisfaction and psychosocial health among Hungarian health care staff: A questionnaire survey. International Journal of Nursing Studies. 2006, 43: 311-318. 10.1016/j.ijnurstu.2005.05.003.View ArticlePubMedGoogle Scholar
- Ilhan MN, Durukan E, Taner E, Maral I, Bumin MA: Burnout and its correlates among nursing staff: Questionnaire survey. Journal of Advanced Nursing. 2008, 61: 100-106.PubMedGoogle Scholar
- Wu S, Zhu W, Wang Z, Wang M, Lan Y: Relationship between burnout and occupational stress among nurses in China. Journal of Advanced Nursing. 2007, 59: 233-239. 10.1111/j.1365-2648.2007.04301.x.View ArticlePubMedGoogle Scholar
- Smedley J, Inskip H, Trevelyan F, Buckle P, Cooper C, Coggon D: Risk factors for incident neck and shoulder pain in hospital nurses. Occupational and Environmental Medicine. 2003, 60: 864-869. 10.1136/oem.60.11.864.View ArticlePubMedPubMed CentralGoogle Scholar
- Viera ER: Why do nurses have a high incidence of low back disorders, and what can be done to reduce their risk?. Bariatric Nursing and Surgical Patient Care. 2007, 2: 141-147. 10.1089/bar.2006.9975.View ArticleGoogle Scholar
- De Jonge J, Dormann C: The DISC Model: Demand-Induced Strain Compensation mechanisms in job stress. Occupational Stress in the Service Professions. Edited by: Dollard MF, Winefield HR, Winefield AH. 2003, London: Taylor & Francis, 43-74. full_text.View ArticleGoogle Scholar
- Hobfoll SE: Conservation of resources: A new attempt at conceptualizing stress. American Psychologist. 44: 513-524. 10.1037/0003-066X.44.3.513.
- Hobfoll SE: Social and psychological resources and adaption. Review of General Psychology. 6: 307-324. 10.1037/1089-26184.108.40.2067.
- Van den Tooren T, De Jonge J: Managing job stress in nursing: What kind of resources do we need?. Journal of Advanced Nursing. 2008, 63: 75-84. 10.1111/j.1365-2648.2008.04657.x.View ArticlePubMedGoogle Scholar
- Taris TW, Schreurs PJG, Eikmans KJL, Van Riet P: Werkkenmerken, welzijn en organisatieprestatie: Een toets van de happy-productive worker-hypothese op organisatieniveau [Work characteristics, well-being and organizational performance: A test of the happy-productive worker-hypothesis on organizational-level]. Gedrag & Organisatie. 2008, 21: 3-18.Google Scholar
- Meijman TF, Mulder G: Psychological aspects of workload. Handbook of Work and Organizational Psychology. Edited by: Drenth PJD, Thierry H, De Wolff CJ. 1998, Hobe: Psychological Press, 2: 5-33. 2Google Scholar
- Sonnentag S, Bayer UV: Switching off mentally: Predictors and consequences of psychological detachment from work during off-job time. Journal of Occupational Health Psychology. 2005, 10: 393-414. 10.1037/1076-89220.127.116.113.View ArticlePubMedGoogle Scholar
- Winwood PC, Lushington K: Disentangling the effects of psychological and physical work demands on sleep, recovery and maladaptive chronic stress outcomes within a large sample of Australian nurses. Journal of Advanced Nursing. 2006, 56: 679-689. 10.1111/j.1365-2648.2006.04055.x.View ArticlePubMedGoogle Scholar
- Winwood PC, Bakker AB, Winefield AH: Investigation of the role of non-work-time behavior in buffering the effects of work strain. Journal of Occupational and Environmental Medicine. 2007, 49: 862-871. 10.1097/JOM.0b013e318124a8dc.View ArticlePubMedGoogle Scholar
- Van Hooff MLM, Geurts SAE, Kompier MAJ, Taris TW: Workdays, in-between workdays and the weekend: A diary study on effort and recovery. International Archives of Occupational and Environmental Health. 2007, 80: 599-613. 10.1007/s00420-007-0172-5.View ArticlePubMedPubMed CentralGoogle Scholar
- Binnewies C, Sonnentag S, Mojza EJ: Recovery during the weekend and fluctuations in weekly job performance: A week level study examining intra-individual relationships. Journal of Organizational Behavior. 2009, 30: 67-93. 10.1002/job.541.View ArticleGoogle Scholar
- Le Blanc PM, De Jonge J, Schaufeli WB: Job stress and occupational health. Introduction to Work and Organizational Psychology: A European Perspective. Edited by: Chmiel N. 2008, Oxford: Blackwell Publischers, 206-230. 2Google Scholar
- Kompier M, Taris T: Assessing methodological quality and biological plausibility in occupational health psychology. Scandinavian Journal of Work, Environment, and Health. 30: 81-83.
- Kompier MAJ, Kristensen T: Organizational work stress interventions in a theoretical, methodological and practical context. Stress in the workplace: Past, present and future. Edited by: Dunham J. 2000, London: Whurr Publishers, 164-90.Google Scholar
- De Jonge J, Dormann C: Stressors, resources, and strains at work: A longitudinal test of the Triple Match Principle. Journal of Applied Psychology. 91: 1359-1374. 10.1037/0021-9010.91.5.1359.
- Goldenhar LM, LaMontagne AD, Katz T, Heaney C, Landsbergis P: The intervention research process in occupational safety and health: An overview from the national occupational research agenda intervention effectiveness research team. Journal of Occupational and Environmental Medicine. 2001, 43: 616-622. 10.1097/00043764-200107000-00008.View ArticlePubMedGoogle Scholar
- Hockey GRJ: Work environments and performance. Introduction to Work and Organizational Psychology: A European Perspective. Edited by: Chmiel N. 2000, Oxford: Blackwell Publishers, 206-230.Google Scholar
- Morris JA, Feldman DC: The dimensions, antecedents, and consequences of emotional labour. Academy of Management Review. 1996, 21: 986-1010. 10.2307/259161.Google Scholar
- Sonnentag S, Niessen C: Staying vigorous until work is over: The role of trait vigour, day-specific work experiences and recovery. Journal of Occupational and Organizational Psychology. 2006, 81: 435-456. 10.1348/096317908X310256.View ArticleGoogle Scholar
- De Jonge J, Dormann C, Van den Tooren J: The DISC Model: Demand-Induced Strain Model: Renewed theoretical considerations and empirical evidence. The Individual in the Changing Working Life. Edited by: Näswall K, Hellgren J, Sverke M. 2008, Oxford: Cambridge University Press, 67-87. full_text.View ArticleGoogle Scholar
- Richardson KM, Rothstein HR: Effects of occupational stress management intervention programs: A meta-analysis. Journal of Occupational Health Psychology. 2008, 13: 69-93. 10.1037/1076-8918.104.22.168.View ArticlePubMedGoogle Scholar
- Cook TD, Campbell DT: Quasi-Experimentation. Design & Analysis Issues for Field Settings. 1979, Boston: Houghton Mifflin CompanyGoogle Scholar
- Scharf T, Chapman L, Collins J, Limanowski J, Heany C, Goldenhar LM: Intervention effectiveness evaluation criteria: Promoting competitions and raising the bar. Journal of Occupational Health Psychology. 2008, 13: 1-9. 10.1037/1076-8922.214.171.124.View ArticlePubMedGoogle Scholar
- Van de Ven B, Vlerick P, De Jonge J: The interplay of job demands, job resources and cognitive outcomes in informatics. Stress and Health. 2008, DOI:10.1002/smi.1192Google Scholar
- Meijman TF: Over vermoeidheid [About fatigue]. PhD thesis. 1991, Amsterdam, Studiecentrum Arbeid en GezondheidGoogle Scholar
- Schaufeli WB, Van Dierendonck D: Utrechtse Burnout Schaal (UBOS): Handleiding [Manual Utrecht Burnout Schale]. Lisse: Swets & Zeitlinger. 2000Google Scholar
- Maslach C, Jackson SE: Maslach Burnout Inventory: Manual. 1986, Palo Alto, CA: Consulting Psychological Press, 2Google Scholar
- Hildebrandt VH, Douwes M: Lichamelijke Belasting en Arbeid: Vragenlijst Bewegingsapparaat [Physical Demands and Work: Motion Questionnaire]. Voorburg: Dictoraat-Generaal van de Arbeid. 1991Google Scholar
- De Jonge J: Job autonomy, well-being, and health. PhD thesis. 1995, Maastricht, Rijksuniversiteit LimburgGoogle Scholar
- Taris T, Kompier MAJ, De Lange AH, Schaufeli WB, Schreurs PJG: Learning new behaviour patterns: a longitudinal test of Karasek's active learning hypothesis among Dutch teachers. Work & Stress. 2003, 17: 1-20.View ArticleGoogle Scholar
- George JM, Zhou J: When openness to experience and conscientiousness are related to creative behavior: An interactional approach. Journal of Applied Psychology. 2001, 86: 513-524. 10.1037/0021-9010.86.3.513.View ArticlePubMedGoogle Scholar
- De Jonge , Peeters , LeBlanc : Emotionele arbeid en positieve werkuitkomsten: De rol van specifieke hulpbronnen in het werk [Emotional labour and positive work outcomes: The role of specific resources in work]. 2006, 19: 345-367.Google Scholar
- Heany CA, Price RH, Rafferty J: Increasing coping resources at work: a field experiment to increase social support, improve work team functioning, and enhance employee mental health. Journal of Organizational Behavior. 1995, 16: 335-353. 10.1002/job.4030160405.View ArticleGoogle Scholar
- Van Gorp K, Schaufeli WB: Een gezonde geest in een gezond lichaam [A healthy mind in a healthy organization]. 1996, Den Haag: VUGAGoogle Scholar
- Mikkelsen A, Saksvik PØ, Landsbergis P: The impact of a participatory organizational intervention on job stress in community health institutions. Work and Stress. 2000, 14: 156-170. 10.1080/026783700750051667.View ArticleGoogle Scholar
- Munz DC, Kohler JM, Greenberg CI: Effectiveness of a comprehensive worksite stress management program: Combining organizational and individual interventions. International Journal of Stress Management. 2001, 8: 49-62. 10.1023/A:1009553413537.View ArticleGoogle Scholar
- Semmer NK: Job stress interventions and Organization of Work. Handbook of Occupational Health Psychology. Edited by: Quick JC, Tetrick. 2003, Washington, DC: American Psychological Association, 325-353. full_text. 2View ArticleGoogle Scholar
- Norman GR, Sloan JA, Wyrich KW: Interpretation of changes in health-related quality of life: the remarkable universality of half a standard deviation. Medical care. 2003, 41: 582-592. 10.1097/00005650-200305000-00004.PubMedGoogle Scholar
- Cohen J: Statistical power analysis for the behavioral sciences. 1977, New York: Academic PressGoogle Scholar
- Goodman JS, Blum TC: Assessing the non-random sampling effects of subject attrition in longitudinal research. Journal of Management. 1996, 22: 627-652. 10.1177/014920639602200405.View ArticleGoogle Scholar
- Ovretweit J: Evaluating Health Interventions. 1998, Buckingham-Philadelphia, PA: Open University PressGoogle Scholar
- The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2458/10/293/prepub
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