Using Matched Samples to Test for Differences in Trade Execution Costs
Ryan J. Davies
Babson College - Finance Division
Sang Soo Kim
The Korea Development Bank
July 13, 2007
This paper provides guidance on how to use matched samples to test for differences in trade execution costs (e.g. quoted and effective spreads). Based on extensive simulation results, we conclude that the best practice is to match firms one-to-one based on market capitalization and share price, and to test for differences between the matched pairs using a Wilcoxon signed rank test. We demonstrate that pre-sorting by industry groups or discarding apparent poor matches may reduce test power. We show that, in general, tests based on one-to-one nearest neighbor matching have comparable power and less size distortion than alternatives that place more weight on distant firms. We find that matching without replacement can reduce size distortion when the control sample is relatively small. We highlight conditions under which matched sample estimation may be preferred to the corresponding event study.
Number of Pages in PDF File: 45
Keywords: Matched samples, market microstructure, bid-ask spreads
JEL Classification: G10working papers series
Date posted: June 3, 2004
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