A non-transitory computer-readable storage medium storing a data processing program, which when read and executed, causes at least one computer to perform data processing of monitoring a person, the data processing program, which when read and executed, causes the at least one computer to perform operations comprising:
- calculating pupil movement and head movement of the person;
- evaluating a suitability degree of a situation in calculating vestibulo-ocular reflex movement based on the pupil movement and the head movement of the person;
- providing the evaluated suitability degree to data relating to the calculated pupil movement and the calculated head movement of the person;
- selecting a first technique of calculating sleepiness based on the vestibulo-ocular reflex movement of the person or a second technique different from the first technique based on the suitability degree provided to the data;
- calculating the sleepiness based on the first technique in response to selecting the first technique;
- and
- calculating the sleepiness based on the second technique in response to selecting the second technique.