Cost-per-Click Pricing for Display Advertising

TLDR

Display advertising is a $25 billion industry with growing revenue, yet publishers face uncertainty in demand, traffic, and visitor click behavior. This study examines a web publisher’s cost‑per‑click pricing model that guarantees a specified number of clicks for posted ads. The authors model the setting as a queueing system where ad slots are service channels whose rates inversely depend on the number of active servers. They derive closed‑form steady‑state probabilities, compute an optimal CPC price that rises with slot count and promised clicks, show that the common click‑through‑rate heuristic can mislead and reduce revenue, and explain the observed CTR drop when switching to cost‑per‑impression pricing.

Abstract

Display advertising is a $25 billion business with a promising upward revenue trend. In this paper, we consider an online display advertising setting in which a web publisher posts display ads on its website and charges based on the cost-per-click pricing scheme while promising to deliver a certain number of clicks to the ads posted. The publisher is faced with uncertain demand for advertising slots and uncertain traffic to its website as well as uncertain click behavior of visitors. We formulate the problem as a novel queueing system, where the slots correspond to service channels with the service rate of each server inversely related to the number of active servers. We obtain the closed-form solution for the steady-state probabilities of the number of ads in the publisher's system. We determine the publisher's optimal price to charge per click and show that it can increase in the number of advertising slots and the number of promised clicks. We show that the common heuristic used by many web publishers to convert between the cost-per-click and cost-per-impression pricing schemes using the so-called click-through-rate can be misleading because it may incur substantial revenue loss to web publishers. We provide an alternative explanation for the phenomenon observed by several publishers that the click-through-rate tends to drop when they switch from the cost-per-click to cost-per-impression pricing scheme.