In this paper we have shown that output effects can have a significant impact on estimated import price elasticities for aggregate classifications. Our results indicate that output effects could reduce estimated import price elasticities for Canada by as much as 10% to 15% for some aggregate classifications. These r&sults tend to understate the importance of output effects for estimated elasticities to the extent that they do not include any output effects of changes in exports and they tend to overstate the importance of these effects to the extent that supply curves for domestic production are less than perfectly elastic. However, they provide order-of-magnitude estimates of the bias caused by output effects when import price elasticities estimated for aggregate classifications are applied to disaggregate classifications of imports. These results also indicate the degree to which a general equilibrium approach may understate the impact on trade of an exogenous change in relative prices by doublecounting within-class output effects. Similarly, they indicate the degree to which import price elasticities estimated for very disaggregate classifications may overstate the case against elasticity pessimism because these disaggregate estimates account for fewer output effects. REFERENCES