RV = Realized Volatility (i.e. historical vol over a period)
It’s true that volatility is based on returns, and bollinger bands are based on prices, but my sense is that there should be a linear mapping between the two so that a strategy that plots buy/sell points based on vol vs bollinger bands is not likely to be all that different. If the bolinger bands are wide, it suggests that the volatility is wide too. Current price level might be an additional variable that messes up the 1:1 correspondence, but I’m still not sure they are materially different, other than some scaling factor equal to one / current price.
I bring up the issue because sometimes we get too excited about the math we do and then use it because we don’t want to have wasted the effort of discovering things. I know that I have occasionally used option implied volatility in tactical asset allocation and my conclusion from comparing it to using historical volatility was that it was a good deal more cumbersome to calculate and not materially more helpful in the strategy.
In general, if you don’t get a marked improvement in your performance by going the more complicated route, you should abandon it in favor of the simpler calculation - that’s because the more complex calculation usually makes more assumptions to make the mathematics work. More assumptions often means there is a greater chance that one of them is not going to apply in a certain situation, and then things can go haywire in unexpected ways.
It’s not always the case, of course, becasue simple models also make assumptions and sometimes the point of the more complex math is to undo some of the simplifications that have been made. I think you may be arguing it here that historical volatility assumes that the future vol looks like the past vol and that implied volatility is a better estimate of future vol because people are using it to pay for their options.
But remember that option vol is not a magical predictor of future vol’s actual value. It almost always biases higher, in part because market markers want to get paid for what they do and the model automatically attributes higher prices to higher implied volatility, and in part because lots of option buyers are scared (or hopeful) that something big is about to happen. Aside from the bias upwards, it also can also be noisier, and then you start looking at things like vol of vol, etc… Sometimes it adds information, other times it just adds noise.
The other reason that some people like to go to more complex math is because it sounds good in marketing, whether it’s one’s own skills or the fund’s performance itself. By arguing you use more complex math, it avoids the question of “why can’t we just hire someone else to use your simple formulas.”
Anyway, these things are judgment calls. I tend to advocate “simple, unless the more complex version has a demonstrably better track record.” But that’s just me.