Whilst the stats may be correct, I suspect the answer, as the article infers, is more to do with the roles in which intelligent men served.
The more intelligent servicemen would have ended up as officers, NCOs or in the Grim Reaper of the 1930s grammar-school generation - RAF Bomber Command. Successive studies have shown that casualty rates in these groups were especially high in WWII.
This came home to roost after the war, with about 150000 of Britains brightest, committed and altruistic future middle-managers dead on the Battlefield.
Were IQ tests used to select recruits in WWII? I can see the need in more technical branches- eg Bomber navigators but what about infantry?
The popular conception is of thick, rich, kids chosen on Character and parental wealth. "Unicorns almost"
I disagree. If the stats were published in a quality journal (which Intelligence is) then they would have been significant. Significance and effect size are also different things. And when calculating significance, chance is also taken into the consideration.
Also, the data they used has also been used to draw conclusions on the role between intelligence and dementia, and also if intelligence is fluid (i.e. changes over the life span) or constant, or if it naturally declines. Almost 500 participants is quiet a lot.
I'm going to be geeky and try and get hold of the original article, too
The article makes it pretty clear that the sample size was easily big enough for the results to be statistically significant. It also points to the likeliest explanation being role-based, i.e. the selection process meant that smarter fellas were ultimately that little bit more likely to end up in harm's way.
It also hypothesises that the more intelligent soldiers might be more likely to feel a commitment to seeing things through; but I think that is probably wrong. I'm sure WWI soldiers were different from 1980s ones, but I don't recall ever thinking that the less intellectual squaddies around me were less brave or committed or ready to man up and get the job done than the smarter ones. In fact I reckon I met a few bright sparks who couldn't do the job as well as fellas whose intelligence they would have looked down on.
I don't have military experience so this might be nonsense. The article says that the study was across all ranks. I'd expect more intelligent blokes, on average, to be the ones who got promoted or comissioned.
Don't identifiable officers and NCOs tend to attract sniper fire ? Could this explain a slightly lower survival rate for the more intelligent?