Another issue is the difficulty of determining causality in laughter research. It may be that people who like to laugh are simply less prone to illness. It could also be the case that people who are healthy are not in pain and are therefore more readily able to laugh. There just isn't enough evidence yet.
其次，笑研究的因果關係很難判定，也許愛笑的人比較不會生病，但也有可能是因為健康的人沒有病痛，才能笑口常開，需要更多的科學論證。