The understanding of workers’ stress in the workplace is attracting growing interest in occupational health psychology. Stress, when uncontrolled, has detrimental psychological and physiological effects on workers’ well-being and performance . Increased levels of stress compromise the immune system, reduce cardiovascular functioning, influence blood pressure and hormone excretion and increase the risk of accidents . In this sense, in the Italian context, work-related stress has become a core topic of occupational research, especially after the introduction of the law (D.Lgs 81/08) which obliges organizations to assess psychosocial risk factors and their impact on workers’ well-being in order to prevent strain. Psychosocial risk factors have been defined as aspects related to the planning, organization and management of the job, as well as to the respective environmental and social contexts that have the potential to produce physical, social or psychological damage . These factors can be related to work content and work context.
Workload and repetitive work have been seen as two psychosocial risk factors of work content which are more associated with workers’ strain . Conditions of high workload are related to different negative work outcomes, such as low work satisfaction, burnout and intention to leave the organization  and negative health outcomes, such as anxiety, depression and myocardial infarction . Results from recent research have revealed that high workload is also causally related to organizational and behavioural outcomes, like, for example, drug abuse , counterproductive work behaviour , absenteeism , bullying at work , low work engagement  and reduced job performance .
Repetitiveness is a further aspect of the content of work that has a negative influence on strain. Some researchers have shown that repetitive work and a lack of control over the work process constitute a threat to health and well-being and are positively associated with blood pressure , physical symptoms and perception of strain .
On the other hand, interaction with customers is one psychosocial risk factor of the work context that may be related to dissatisfaction and cause psychological strain . Several researchers underlined that customer management has not been investigated enough as a source of stress in the literature of work-related stress, although 22% of negative events reported by workers occurred when dealing with ‘problem customers’ and some anger-provoking events related to mistreatment by customers [16, 17].
In spite of the large body of studies on work-related stress, most of the research has focused on self-report measures to determine both the stressors and the outcome variables [18, 19]. Self-reported perceptions may be influenced by workers’ interpretations and this situation has been repeatedly criticized because correlations may be artificially enhanced by conceptual overlap  and common method variance [21–23], producing spurious correlations .
An alternative methodology is objective assessment based on observational approaches which are independent of workers’ interpretation [25–27]. On the other hand, the same ‘objective’ stressor at work can trigger a serious strain in one person and not in another. As a consequence, the use of objective measures alone cannot be considered as a solution. Starting from these premises, our paper does not aim to test a specific model about stress but the whole discussion is based on the assumption that strain relies on two components, a subjective appraisal and an objective work setting. Main models are compatible with such approach, as Demand-Control (DC) model , the Effort – Reward imbalance (ERI model)  and the Job-demands resources model . All of them state that, in order to measure the impact of stress, it is necessary to consider workers’ perception.
However, few studies have tried to combine subjective and observational data  and compare several kinds of objective assessments with self-reports . One example of the combination of these two measures is the ISTA method (Instrument for Stress-Oriented Task Analysis) , which starts from the concept of action regulation, which describes work from a psychological perspective as accomplished by goal-oriented action  and tries to match workers’ subjective perception with expert assessment through observation of the workers’ work environment. However, in the ISTA method the subjectivity of the workers was replaced by the subjectivity of the observer, who has to answer to the same self-report rating scales administered to workers observing them. For instance, in order to measure variety (boredom) objectively, the judge evaluates whether the workers receive recurrent and similar tasks (person A) or tasks that are varied and different (person B), using a five-point rating scale ranging from one (‘exactly like A’) to five (‘exactly like B’) .
In order to overcome the limitation of the subjectivity of observers, we developed a new observational checklist, in which the variables were operationalized using more observable aspects of content of tasks and context of work. For instance, we have operationalized the variety (boredom) with the observable number of different tasks performed in the 30 minutes of observation, instead of asking the observer to answer on the same rating scale administered to workers with self-report scales.
This observational checklist is one of the tools used by the STress Assessment and Research Toolkit (St.A.R.T.) method which combines the quantitative and qualitative methodological approaches by assessing work-related stressors using different kinds of data: i) organizational archival data (organizational indicators sheet); ii) qualitative data (focus group); iii) worker perception (questionnaire); iv) observational data (observational checklist). The integration of these sources of data can reduce the theoretical and methodological bias related to stress research in the work setting (e.g. common method variance), and allows researchers and professionals to obtain a more reliable description of workers’ stress than through the use of a single analysis tool, providing a more articulate vision of psychosocial risks . Some of these instruments had already validated [36, 37].
In this paper, we considered two sources of quantitative data collected using the St.A.R.T. method, that is, observational data collected through a checklist and subjective data collected through an individual self-report questionnaire, and we presented the empirical results of the correspondence and integration of these two kinds of data.
In particular, the aims of this study were:
To examine whether the data collected through the self-report questionnaire were associated with the rating data collected through the observational method in three dimensions: boredom and workload (content of work), and relations with customers (work context);
To verify which psychosocial risk factors, subjective and objective, are related to two workers’ health outcomes: psychological health and emotional exhaustion.