A researcher investigated the relationship between physical fitness levels and workplace productivity. Employees at a multinational corporation were asked to complete a self-report exercise log questionnaire on their smartphones while commuting home on a metropolitan subway. The questionnaire consisted of 8 open-ended questions about their physical activities. The data collection occurred over a four-week period, with participants completing the questionnaire at varying times of the evening; some did so during peak rush hour when trains were packed and noisy, while others completed it late at night in empty, quiet carriages.