with any stat that does not have increasing or diminishing returns you can simply divide the stats given by the proc by the % uptime. so for something like DMC:G if it gave 400str and was up 25% of the time you could say the proc was effectively 100str. However with stats like arp, and crit, their DPS value varies depending how much of that stat you have, and as such you can't make give those procs an equivalent constant stat value
Just a small point here, I've never done any maths on procs before and I'm sure someone can explain it better than me but the 'maths' part wouldn't be the stat gain of the trinket such as +300 str, it would be something like the effect of the proc on dps. Stats don't necessarily increase your dps in a linear fashion, for example in the case of arp, having 0% arp 90% of the time and 100% arp 10% of the time is not equivalent to having 10% arp 100% of the time.