Define the relationship and the hedge
Correlation describes co-movement over a chosen sample. It does not measure whether a price ratio or hedged spread has a reliable long-run relationship. That requires a separate model with its own assumptions and validation. Two companies can share sector exposure while their business prospects permanently diverge.
Define the spread and hedge ratio before measuring it. Dollar matching, share matching and estimated sensitivity matching are different constructions. The short side also requires a feasible borrowing arrangement and can incur fees, dividend obligations, recalls or forced closure. A long position does not cap losses on a short stock.
Worked example: both legs lose
Take a fictional long of 200 shares of A at $50 and a short of 100 shares of B at $100. Each side starts at $10,000, so net dollar exposure is initially zero but gross exposure is $20,000.
If A falls to $45 and B rises to $110, the long loses $1,000 and the short loses $1,000. Total loss is $2,000 before borrowing and trading costs. Equal initial dollars did not remove relative-price risk. If A and B both rise 10%, their initial dollar gains and losses offset before costs; these are two different scenarios, not predictions.
A spread can keep moving away
A fitted hedge ratio can change, and a spread that appears extreme can keep widening. Statistical evidence from one period may not survive a merger, regulation change or funding shock. Correlation calculated from price levels can also be misleading; the choice between prices and returns must be explicit.
Look for breaks in the relationship
Compare available closed daily, weekly or monthly bars over aligned dates and note periods when the assets behaved differently. Document corporate events that could change their relationship. Student Wyckoff Pro can support this chart review; spread estimation, borrowing availability and trade execution require separate tools and records.
Primary sources
Sources explain the mechanics and limitations; the editorial examples use invented numbers rather than market quotations.
Your next practical step
Explore the available closed daily, weekly and monthly bars in the analysis workspace.
Open the first-chart instructions ↗