Epidemiological case-control study into the relationships between chronotype, shift work and accident frequency. Phase 1: Feasibility study

Status:

completed 10/2014

Aims:

An individual's peak performance levels at a given time of the day are influenced by their chronotype. The term "chronotype" is used in chronobiology to categorize human beings according to their biological clock. Their sleeping and waking phases and peak performance occur at different times of the day. A distinction is drawn between early types ("early birds"), normal types and late types ("night owls"). This gives rise to the hypothesis that the risk of accident among shift workers is greater when they are assigned to shifts without consideration being given to their chronotype.

The aim of the project as a whole was to study the influence of appropriate shift assignment (early types not assigned to the night shift, late types not to the early shift) upon the incidence and severity of accidents. Results of this research were to be used in the future in order to reduce accident risks and work-related health hazards by improvements to shift planning. At the beginning of the project, a feasibility study was conducted in order to review the availability of data for the study.

Activities/Methods:

Plants and divisions of Siemens AG were recruited during the feasibility study. The employee accident reports were inspected and documented.

Altogether, approximately 50 cases, i.e. employees of Siemens AG working alternating shifts who had suffered a reportable accident during the previous three years, were to be recruited for participation in the project. Siemens AG then conducted surveys of these shift workers with the aid of MCTQ Shift (Munich Chronotype Questionnaire for shift workers). The survey covered data on the shift, chronotype, sleep behaviour and leisure behaviour. The data obtained were reviewed for their quality and usability, and then analysed by the IFA. The results of the feasibility study are intended to deliver information on whether a study with this design could be conducted with a larger number of participants.

Results:

Four of Siemens AG's plants were recruited for the purposes of the feasibility study. Shift workers who had suffered a reportable accident in the previous three years were contacted. The personal chronotypes of workers agreeing to participate in the study were determined by means of a questionnaire. 66 participants were questioned, of which 58 were included in the analysis. The occupational physicians anonymized the accident reports and merged them with the chronotyping questionnaires. An identification number on the accident report and chronotyping questionnaire enables the accident report, chronotyping questionnaire and data record to be linked for the purpose of analysis whilst at the same time assuring anonymity of the participants.

The incidence and severity of accidents suffered by the study participants (cases) was compared with that of a general population for the purpose of analysis. The result reveals an increase in the risk of suffering an occupational accident as a function of the chronotype when work is performed in an unfavourably timed shift. The risk increases from 1.3 for moderate early/late types through 1.5 to 1.8 for distinct early/late types. The very early chronotypes (preferred sleep window between 22:00 and 6:00 or earlier) and the very late types (preferred sleep window between 3:00 and 11:00 or later) have an up to 1.8 times greater risk of suffering an occupational accident when working in unfavourable shifts (night and early shifts respectively). A possible main study for further validation of the results would appear advantageous.

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