Digital Stress Induction in Daily Life Using the Salzburg Mobile Stress Induction (SMSI): Development and Ambulatory Evaluation Study.

Background: The use of digital technology enabled examining stress in everyday life. However, ambulatory research depends on the natural occurrence of stressful situations while most standardized stress inductions rely on cost- and labor-expensive laboratory experiments, which are limited in their infrequent applicability.

Objective: We developed the Salzburg Mobile Stress Induction (SMSI), a newly conceptualized toolbox including 6 different stress-inducing paradigms (Matrices test, Cube Net test, Arithmetic test, Number Series test, Word Scramble test, and Word Pair test) and 1 control paradigm (Caesar Cipher test), which are based on cognitive performance tests. These 7 tests aim to provide researchers with an open-access, standardized method to repeatedly induce stress in an ambulatory setting.

Methods: We recruited university students from a local university and through a crowdsourcing platform for a preregistered ambulatory study. After completing a web-based survey, participants used the m-path app on their smartphones to conduct the 7 SMSI tests in a randomized order over 4 days. By comparing the stress-inducing tests with the control test, we investigated changes in momentary negative and positive affect from baseline (t0) to between (t1) and after (t2) each test using the International Positive and Negative Affect Schedule Short Form.

Results: A total of 100 participants (60/100 women; mean age 24.43, SD 6.21 years; 69/100 local sample; 31/100 crowdsourcing sample) completed all 7 SMSI tests. Participants' negative affect significantly increased during all 6 stress-inducing tests compared to the control test from t0 to t1 (Ps<.001) and from t0 to t2 (Ps<.001) with medium to large effect sizes (η_p²s=0.10 to 0.30). Post hoc pairwise comparisons showed significant increases of negative affect during all stress-inducing tests from t0 to t1 (Ps<.001) and from t0 to t2 (Ps<.001) and a slight increase in the control test from t0 to t2 (P=.006). Reported positive affect significantly differed between the stress-inducing tests and the control test from t0 to t1 (Ps<.001) and from t0 to t2 (Ps<.001) with medium to large effect sizes (η_p²s=0.14 to 0.33). Post hoc pairwise comparisons revealed a significant increase in positive affect in the control test from t0 to t1 (P<.001) and from t0 to t2 (P<.001) and varying significant decreases to nonsignificant changes in the stress-inducing tests over time (Ps>.99 to <.001).

Conclusions: The SMSI presents novel and easy-to-implement standardized stress induction procedures to repeatedly induce stress in ambulatory research. We discussed new opportunities for positive eustress inductions and outlined subsequent validation studies combining physiological stress assessment and ambulatory methods. The development of additional language versions of the SMSI is illustrated.