A number of methods have been used to measure the extent of illegal logging and the trade in illegal wood-based products. These include an assessment of discrepancies in trade data between exporting and importing countries, wood-balance analysis, and the results of the expert perceptions survey which included several questions about the nature and extent of illegal logging.
Wood balance analyses could only be undertaken where robust national data could be obtained. Such analyses compared the legal supply of timber (from official records of harvest and imports) with consumption (based on domestic consumption and exports). The gap between supply and consumption can indicate the existence and extent of unreported and hence potentially illegal logging.