Here’s a thought that may address the risk ranges “shape” changing when other obvious things don’t (like the VIX vs SPX):
It’s possible he is using something such as implied call vol and implied put vol for the ranges.
Say what?
Calls and puts can have different implied vols (prices). This is a function of the market wanting to own more of one or the either, which changes price. Now why does this matter? Numerous studies have indicated that implied vol options prices have information not found in share prices. (https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2695145).
Bloomberg has a field in their API for call and put ivol. They are presumably taking a series of options (both puts and calls), and are calculating the Ivol in a similar way as in either the VIX (here: https://www.macroption.com/vix-calculation/) or weighting by OI maybe.
Why would this be useful? Let’s say you calculated call IVOL at 25 and put IVOL at 35. That is an annualized 1SD expected move. If we agree that there is data embedded in options (I do), and that’s what we’re trying to capture, we can make that into a risk range. But we need to pick the number of days. If the average days to expiration of the options that are being used in the IVOL calcs is 30 days. Remember that annualized IVOL #s use 365 day calendars (not 252).
call IVOL = 25% * √(1/365) x √(2/π) = 1.04% ‘implied average daily move’.
put IVOL = 40% * √(1/365) x √(2/π) = 1.67% ‘implied average daily move’.
Important: (a)1 SD is not the same as average daily move. I use ADM instead of SD as options are priced using mean outcomes, and people replicate hedges daily. (b) I am using 365 days as that is the standard as how vanilla options are priced. RV uses 252, and some some OTC vol swaps do use 252.
So, you want to think of a risk range in the context of some # of days? Let’s pick 18 days for fun.
call IVOL = 25% * √(18/365) x √(2/π) = 4.43% ‘implied average 18 day move’.
put IVOL = 40% * √(18/365) x √(2/π) = 7.09% ‘implied average 18 day move’.
Now, we need not worry about a MA for this calc, as we are using implieds. On realized, we need to think about the mean that is going into the calc of the SD/ADM.
How do I test this? Well I don’t know the series of options IVOL assumptions to be used. Maybe it’s the way Bloomberg does it, maybe not, no idea. So, let’s say I were to use AAPL Ivols over the next 30 days. (there isn’t much difference in AAPL between call and put IVOL).
| AAPL ATM Options |
|
|
|
|
|
|
| Expiration |
IV Call |
IV Put |
|
| 23-Oct |
38.50% |
39% |
|
| 30-Oct |
48% |
48% |
|
| 06-Nov |
48% |
49% |
|
| Mean |
44.8% |
45.3% |
|
(this method above is definitely wrong, I should be using more strikes and adjusting to variance contribution, but here ya go)
call IVOL = 44.8% * √(18/365) x √(2/π) = 7.94% ‘implied average 18 day move’.
put IVOL = 45.3% * √(18/365) x √(2/π) = 8.03% ‘implied average 18 day move’.
AAPL closed Oct. 15, 2020 at $119.02. That would give it a range based on my method of $109.90 – $128.47. Not bad eh? I’ll note that there was very little difference between put and call IVOL, so it wasn’t a great candidate.
One point regarding vol of vol. If you use a wider array of option strikes (mainly if you start incorporating OOTM strikes in the call IVOL and put IVOL strikes, unlike what I did), you can start incorporating some other embedded information. Skew is valuable data that may change the risk range (particularly to the downside). This would be weighted to the contribution to that expiration’s overall variance. This would also pick up some gamma pricing and vol of vol data. In fact, certain option strategies like this one (https://www.fidelity.com/learning-center/investment-products/options/options-strategy-guide/1×2-ratio-volatility-spread-calls) expose you to vol of vol because of the structure and the OOTM calls that you are long.