Put/Call Skew
What it measures
A simplified proxy for the industry-standard 25-delta skew: the implied-volatility spread between a roughly 10%-out-of-the-money put and a roughly 10%-out-of-the-money call at the nearest-to-30-day expiry.
Formula
Skew ~= IV(~10% OTM Put) - IV(~10% OTM Call)
Normal range
Positive means the market is paying more for downside protection (puts pricier); negative means more demand for upside exposure (calls pricier).
How it fails
This is explicitly an approximation, not the real 25-delta calculation (which needs a full option-pricing delta model this project doesn't compute) - useful for direction of skew, not precise magnitude comparison against sources that do compute true 25-delta.
Related metrics
DVOL
Bull read
Negative skew (calls pricier) suggests the options market is paying up for upside exposure.
Bear read
Positive skew (puts pricier) suggests demand for downside protection - but hedging demand isn't the same as a prediction that downside will happen.