Workers’ compensation is often viewed as one of the more stable parts of an insurance program. It tends to renew with fewer surprises, which can lead to it receiving less attention over time.

At the center of it is the experience modification factor, or EMR (often referred to as the “mod”). It is designed to measure how a company’s workers’ compensation loss experience compares to others of similar size and industry. In simple terms, it reflects how actual claims history compares to what is statistically expected.

A mod of 1.00 represents expected performance. If it rises above that level, it indicates a higher-than-expected loss profile and results in increased premium. If it falls below 1.00, it reflects better-than-expected performance and generates a credit.

At a basic level, the formula compares actual losses to expected losses:

EMR ≈ Actual Losses ÷ Expected Losses

If actual losses align with expectations, the mod remains around 1.00. If they exceed expectations, the mod increases. If they fall below, the mod decreases.

In practice, the calculation is more nuanced. Losses are split into primary (smaller, more frequent claims) and excess (larger, less frequent claims), with primary losses weighted more heavily. This is why frequency has a greater impact than severity. The calculation also incorporates multiple years of data (typically three policy years, excluding the most recent), meaning trends build over time rather than overnight.

While the concept is straightforward, how it develops over time is less obvious. Two companies with similar total claim costs can end up with very different mods depending on how those losses occur.

A common assumption is that large claims are the primary driver of a mod. In reality, frequency plays a much bigger role than most expect.

A pattern of smaller, recurring claims can have a more significant long-term impact than a single large loss. It signals to the market that there is an ongoing exposure rather than an isolated event.

This is often where companies run into issues. Claims that feel routine at the time begin to accumulate, and over time that pattern drives the mod higher. By the time it becomes visible in pricing, the trend has already been established.

Improving a mod is not just about avoiding major incidents. It comes down to how everyday exposures are managed. Early reporting, active claims management, and return-to-work practices all play a role. These are operational decisions, but they directly influence how the insurance market evaluates risk.

The impact of the mod does not stop at a single policy. Carriers are increasingly evaluating loss experience across multiple lines when underwriting an account.

A deteriorating mod can influence how liability and umbrella coverage are priced and structured. Over time, it becomes a signal of how risk is managed across the organization, not just within workers’ compensation.

From our perspective, the most consistent issue behind elevated mods is not severity, but frequency. Organizations that take a proactive approach to managing smaller claims tend to see measurable improvement over time. Those that treat them as routine often experience continued pressure on pricing.

The companies that perform best are the ones that connect claims activity to operational decisions. When safety, reporting, and claims management are aligned, the results tend to follow.