There might be different ways of answering that depending on something Professor Quaid raised: What are we concerned about under the Competition Act? It's something I've expressed concern about as well. We're not entirely clear on that. Let me start there.
Market power, as most economists would think about it, is the ability to act independently of competitors to a significant extent. It's being able to raise your prices above marginal cost in a way that is harmful to consumers, because consumers who would be willing to buy something at a competitive price are priced out of the market and there's a loss to them as a consequence. That, to me, at least if you're thinking about it economically, is the concern that lies at the heart of the Competition Act. We're worried about people not being able to participate in markets because some firms have control and can act independently of competitors. Competitors aren't driving down prices in a way that disciplines them, so they can act independently.
Market power may not be present even with significant market share if there's a significant threat of entry, for example. If entry is really easy and you raise your prices, you'll attract entry. There's a kind of discipline there, even if in the moment you have a significant market share. That's just one example.
Another would be that you have a significant market share but have a product that's not as good as one that was just innovated. Your market share is good now, but it's going to decline over time because you're facing discipline from competitors that prevents you from exploiting your customers.
Market share can be an indicator of market power, to be sure, but as I think Professor Ross put it, it's a very weak indicator. There are other things going on that matter too.