crew changing by ship is a logistical no go, firstly supply vessels only have bed capacity for say 20 pax, thats immediately a factor if the vessel has to sit tight in weather as is often the case in the NNS, secondly half the older platforms dont have the required safety features on the cranes (double braking system) to routinely perform basket transfers.
For the amount of vessels that would be required to service an industry operating predominantley 2/3 rota programmes the north sea would look like a sunday boating pond and be coloured orange with the non ending waves of sea sickness being produced............its not even factored in the equation now or we would not have had period of being stuck for 4 or 5 days due to Wx or fog (however if you made it half way to lerwick it was happy days)
As for statistics, well they are as good as whats put into the machine that spits them out, yes they carry value but can also be twisted and misleading.
Fact : Its statistically proven that your more like to have a car accident if your 18 - 22 years, male, wearing underwear and driving during the day......so whats the answer......knickers off on the road, stats watch how you use them.