Why might a concentration ratio be a poor measure of actual industry c

Why might a concentration ratio be a poor measure of actual industry competition?

What will be an ideal response?

ANSWER

Concentration ratios measure national competition within a line of products that are substitutes in production. Where there is much international competition, where competition is regional rather than national, where there is competition from products that are substitutes in consumption but not production, and for other reasons listed in the text, competition ratios may be poor measures of competition.