Straightforward differentiation of (1), (2) and (3), verifies that higher d's (greater efficiency differences) correspond to higher profitability for the efficient firms, lower profitability for the inefficient firms, and higher industry profitability. Therefore, high levels of industry profitability indicate the presence of hard-to-replicate efficiency levels, making the industry less attractive for inefficient firms. (See also Lippman and Rumelt 1982, p. 425.) Conversely, for efficient firms, the industry is more attractive if industry profitability is high. While our result is derived for homogeneous products, it is equally valid for differentiated firms since such firms also benefit from lower cost positions.
Next, consider the effect of industry growth. Standard economic reasoning (Porter 1980) argues that industries with high growth contain many inefficient firms and support high prices relative to volume. Therefore, in markets with high growth we can
expect a "high" value of a and a "low" value of b. Differentiating 'Ire - 7rj with respect to each of these parameters verifies that values indicating high market growth make the industry relatively more attractive for inefficient firms than for efficient firms.
Therefore, it is more crucial that an efficient firm participates in high growth markets.
Summarizing, the profitability of efficient and inefficient firms depends on d, the
differences in efficiency; a, the fraction of firms which are inefficient; and b, the inverse price sensitivity of the market. Both average industry profitability and the profitability of the efficient firms increase as efficiency differences increase. On the other hand, the same mechanism causes the profitability of inefficient firms to decrease. The amount by which efficient firms outperform inefficient firms is smaller (0 if there are relatively more inefficient firms, and (2) if industry prices are less volume sensitive-conditions
typically associated with high rates of industry growth.
We here wish to apply the above theory to the special case of diversified firms. In doing so, we will argue that some types of diversifiers, ceteris paribus, are more likely to be inefficient.