I would treat the report as an indicator to helmet effects. Other reports can also be considered etc. Data from NZ is useful to consider with data on cycling levels and injuries.
One submission included the following;
H) Increased risk of injury per cyclist since helmet laws were introduced
Several analyses have compared numbers of injuries with the numbers of cyclists. They all suggest that injuries per cyclist have increased from what would have been expected without helmet laws.
In New Zealand, from 1989 to 2011, average time spent cycling (on roads and footpaths) fell by 79% for children aged 5-12 (from 28 to 6 minutes per person per week) and 81% for 13-17 year olds (52 to 10 mins/person/week).
Adult cycling declined from 8 to 5 minutes/person/week then trended back up to 8 minutes. Graphs of cycle use over time provide strong evidence that the requirement to wear a helmet discouraged cycling. The reductions in cycling were accompanied by increased injury rates. Between 1989 and 2012, fatal or serious injuries per million hours of cycling increased by 86% for children (from 49 to 91), 181% for teenagers (from 18 to 51) and 64% for adults (from 23 to 38). Robinson DL, Submission, No 411 Senate Inquiry into personal choice and community impacts http://www.aph.gov.au/Parliamentary_Bus ... ubmissions
Another useful piece of information also came from Robinson;http://www.cycle-helmets.com/robinson-head-injuries.pdf
it gives details showing helmet wearers are more likely to hit their helmets when they do fall off.
Listing the pros and cons of helmet effects that may affect the accident rate tends to show they will likely add to the overall number of falls, see http://www.ta.org.br/site2/Banco/7manua ... Helmet.pdf
In addition other research also finds concerns, e.g. Erke and Elvik 2007 examined research from Australia and New Zealand and stated: "There is evidence of increased accident risk per cycling-km for cyclists wearing a helmet. In Australia and New Zealand, the increase is estimated to be around 14 per cent." The findings were based on six reports, four from when legislation was in place.
Erke A, Elvik R, Making Vision Zero real: Preventing Pedestrian Accidents And Making Them Less Severe, Oslo June 2007. page 28 https://www.toi.no/getfile.php/Publikas ... 7-nett.pdf
Of course research from the the 1980's to now should have considered this issue in detail. most of the research focus on if a helmet will provide protection in the event of an impact. If the accident rate changes with helmet use then the overall safety assessment becomes more uncertain. After 30 years of helmet research it cannot be proven that helmets improve safety overall. it can be shown that helmet legislation discourages cycling. These two issues do sit well with supporters of helmet legislation, because it is not justified.
The following is a reasonable overall guide.http://www.cyclinguk.org/campaigning/vi ... le-helmets