# Interpreting the bid-ask spread calculated by the Corwin and Schultz (2012) method

On the homepage of Corwin (https://www3.nd.edu/~scorwin/) there is an excel spreadsheet which showcases the calculation for the bid-ask spread, which is expressed as a percentage. What is this a percentage of - the high low range of the second, single bar or the adjusted two bar range of the two bars involved in the calculation?

• When the bid ask spread is expressed as a percentage, it is generally understood as "a percentage of the price of the stock" i..e. as a percentage of the bid-ask midpoint $\frac{a-b}{(a+b)/2}$. The Corwin procedure attempts to estimate this quantity. – noob2 Dec 13 '18 at 17:51