“In practice, a small ES can be very impressive if, for example, the outcome is difficult to change (e.g. a personality construct) or if the outcome is very valuable (e.g. an increase in life expectancy).  On the other hand, a large ES doesn’t necessarily mean that there is any practical value if it isn’t related to the aims of the intervention (e.g. religious orientation).”
- Neill & Richards (1998, p.3)