Researchers in positive psychology study empirical factors that lead to life satisfaction,[15] full engagement in activities,[16] making a fuller contribution by utilizing one's personal strengths,[17] and meaning based on investing in something larger than the self.[18] Large-data studies of flow experiences have consistently suggested that humans experience meaning and fulfillment when mastering challenging tasks, and that the experience comes from the way tasks are approached and performed rather than the particular choice of task. For example, flow experiences can be obtained by prisoners in concentration camps with minimal facilities, and occur only slightly more often in billionaires. A classic example[16] is of two workers on an apparently boring production line in a factory. One treats the work as a tedious chore while the other turns it into a game to see how fast she can make each unit, and achieves flow in the process.