A Note on the Empirical Measurement of Vertical Integration

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 In a recent article in this journal, Tucker and Wilder [4] (hereafter T & W) examine some determinants of trends in vertical integration across both industries and firms, using the ratio of value added to sales as an index of vertical integration. In their industry-level analysis, T & W calculate this index from Census four-digit SIC industry data. The purpose of this note is to explain why Census data are inappropriate for this use.