Two Kinds of Number

Lagging indicators count outcomes that have already happened: injuries, spills, lost days, enforcement notices. Leading indicators count the activity intended to prevent them: inspections done, actions closed on time, permits field-verified, training delivered against plan.

Why lagging alone fails

• Rare events are statistically noisy. A site with two recordable injuries last year and one this year has not improved by 50%; it has moved within normal variation.
• They reward suppression. The cheapest way to reduce recorded injuries is to record fewer of them.
• They arrive too late. By the time the number moves, the failure has already occurred.

Why leading alone fails too

Activity is easy to manufacture. A site can complete every inspection, close every action and still hurt people if the inspections look at the wrong things. Leading indicators need a quality dimension — not just how many, but what they found and what changed.

Injury rates measure how well you are doing at not being unlucky. Process and activity measures tell you whether you are actually managing risk.