To the Editor Using publicly available data, Dr Wouters and colleagues¹ estimated a mean cost for research and development of 63 products of $1559.1 million. This finding is noteworthy given that DiMasi and colleagues² estimated a mean research and development cost of $2800 million based on data for 106 products developed by 10 large firms. Wouters and colleagues attributed this difference, among other reasons, to higher clinical costs incurred by larger pharmaceutical firms in the sample of DiMasi et al.² The sample used by Wouters and colleagues contained 41% of US pharmaceutical firms with a market capitalization greater than $10 billion and 5% of all pharmaceutical firms with less than $1 billion. Thus, smaller firms were not oversampled, as claimed.