Mental strain and the problem of repeated measurements

In the past, stress and strain arising from the execution of mentally demanding tasks have been measured by means of surveys. Such methods require repeated investigation of the individual perceptions and valuations during task fulfilment to record time-dependent changes in strain levels. However, it is possible that the individual measurement procedures employed in surveys--as artefacts--may cause a change in the stress situation and subsequently in the resulting mental strain. The results of the experiments carried out to investigate this hypothesis verify that repeated measurements have a similar effect as a short break. The repeated measurements taken during progressive studies are, therefore, likely to affect the conditions of stress. A change in the level of mental strain recorded can be expected, particularly if the post-test rating is preceded by a long period of low stress before or during which an additional measurement of strain is implemented.