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α: calibrated so average coauthorship-adjusted count equals average raw count
In U.S. firm-level data, large firms increase their spending on customer capital significantly more than small firms following an interest rate decline. We interpret this evidence in a model with product market frictions where heterogeneous firms strategically advertise to build a customer base. When a firm advertises, it shifts customers’ demand away from competitors. This externality is especially severe when firms have a sizable existing customer base, discouraging smaller competitors and making them less responsive to interest rate shocks. The model provides a rationale for the rise in market concentration and market power in recent decades, while interest rates fell.