We show that estimates of the half-life of deviations from LOOP are biased when not taking into account the precision when aggregating over types of goods. Using a comprehensive dataset with monthly price data for 124 homogeneous products across regions in Denmark over the period 1997–2010 we find a large positive aggregation bias. On average, we find that the half-life is 8.4 months when taking the bias into account compared to 28.7 months when applying the standard method. The heterogeneity in estimated half-life can be explained by price stickiness, distance between regions and whether the good is traded or non-traded.