Earnings Response Coefficient (ERC)

The earnings response coefficient measures how much a company's stock price reacts to a given amount of earnings surprise. Formally it is the slope of the relationship between a stock's abnormal return and its unexpected earnings around an announcement. A high ERC means the market moves the stock a lot for each unit of surprise; a low ERC means the same surprise barely registers. The ERC is a way of asking how informative and how credible a company's earnings are.

What it captures

Not all earnings surprises are treated equally. A beat from a stable, high-quality business can move the stock sharply, while an identical beat from a volatile or low-quality business moves it little. The ERC quantifies that difference. Research has identified several factors that systematically raise or lower it:

• Persistence. If a surprise is likely to recur (a durable improvement rather than a one-off), the market capitalizes it more heavily, raising the ERC.
• Risk. Higher-risk stocks have lower ERCs, because future earnings are discounted more heavily, so a given surprise is worth less in present value.
• Growth. Higher-growth firms tend to have higher ERCs, since a surprise signals a larger stream of future earnings.
• Earnings quality. Cleaner, more predictable accounting raises the ERC; noisy or aggressive accounting lowers it because the market trusts the number less.
• Interest rates. Higher rates lower ERCs by discounting future earnings more.

Worked example

Two companies each report earnings 10% above expectations. Company A is a stable, low-debt compounder; Company B is a volatile, highly leveraged cyclical.

• Company A's stock jumps 6% on the beat: a high ERC.
• Company B's stock rises just 1.5% on the identical 10% beat: a low ERC.

The market is saying A's surprise is more persistent and more credible, so it is worth more per unit. The ERC formalizes the intuition that who beats matters as much as by how much.

Why it matters

The ERC connects accounting information to market value. For investors, it explains why two companies can post similar beats and see very different price reactions, and it warns against assuming every earnings surprise deserves the same response. For companies, a low ERC is a signal that the market discounts their earnings, often due to perceived risk or poor earnings quality, and that improving predictability and transparency can raise how much each dollar of earnings is rewarded. Paired with standardized unexpected earnings, which measures the size of the surprise, the ERC measures the market's sensitivity to it.