I came across this, which I felt was comprehensive and very readable.
Bicycle Helmets: A Scientific Evaluation
If found this quote amusing, on page 156 "In 1996, a leading Australian
manufacturer said, “The helmet industry has certainly changed over the past 16 years and bicycle helmets are now a consumer product. Heavy, bulky style hard helmets have virtually been replaced by the lightweight aerodynamic micro shell styles that we see today. I
n fact the bicycle helmet industry has become almost a fashion industry and this is all related to consumer demand."
BTW, have a look at table 2 on page 166 and this text: "Clearly, adult cyclists did not share commensurately in the general improvement in road safety. Nor did child cyclists; the fall in casualties to them was about the same as the decline in participation. No benefit from compulsory wearing of helmets is evident; rather, it would appear that the risk to cyclists increased. Indeed, from studies in Australia and New Zealand Elvik and Vaa estimated that mandatory wearing of helmets increased the risk of injury per kilometre cycled by 14% [100]. "