It's important to understand the difference between slips, mistakes, and calculated risks, and where these errors come from, so we can reduce them. This is important, because most of these errors go unnoticed or are ignored. If you don't step in when you see a slip or mistake made, or when someone takes a calculated risk, you're taking a calculated risk yourself--figuring that an injury will not occur.

Last month I discussed how punishment usually does more harm than good when it comes to correcting errors. Now let's explore the nature of errors so we can better investigate and prevent them.

To understand how we make errors, consider how we process information. We're continually taking in information, evaluating it, and acting on our interpretations and decisions. Errors can occur at each stage of this information processing cycle.

Type of errors When we miss a stop sign or misread a dial, we are at risk for an input error. This is the failure to detect, recognize, or identify. It could be because our eyesight is poor (a physical limitation) or because there is glare on the dial (an environmental condition). We can also tune out signs and warnings in a process called habituation. I'm sure you've seen this in the workplace: As people become more competent and confident, they pay less deliberate attention to what they are doing, and then the potential for slipping up increases.

Judgment errors come when we interpret our sensory input and decide on a course of action in a way that puts us--and possibly others--at risk. Output errors occur while executing a task. These are the risky performance behaviors that we can readily observe. Limitations in strength, reaction time, coordination, or endurance can cause these errors, brought on by psychological or physical variables including fatigue, distress, alcohol, age, arthritis, or a cumulative trauma disorder, to name a few. Experienced workers can error by operating on "automatic pilot." More often, though, errors of execution occur when work processes do not adequately account for human limitations and characteristics.

Slips versus mistakes Now for some definitions. Mistakes and calculated risks occur when we evaluate a situation and decide how to act. New hires make mistakes when they don't know the safe way to perform a task, or when they don't understand the need for special precautions. They take calculated risks supported by supervisors or coworkers. Experienced workers make mistakes by taking safety for granted. Their skills encourage taking calculated risks, as does their knowledge that soon and certain benefits outweigh improbable costs.

To understand more about slips, which generally occur in the input and output stages of processing information, Donald A. Norman offers helpful definitions in his book, "The Psychology of Everyday Things" (1988, Basic Books, New York).

Capture errors occur when our actions seem dictated by familiar routines. You borrow someone's pen and put it in your own pocket because that's what you always do with pens. Or you start a new task at work and find yourself using old habits.

This is one reason to get in the habit of practicing the safe way of doing something, regardless of the situation. When basic safety-related behaviors become habits, we can turn our attention to higher-level thinking, and the probability of an error is reduced.

Description errors arise when the difference between correct and incorrect actions is slight. Do you have switches on operating equipment that are similar and in close proximity, but control different functions? How unsafe is it to throw the wrong switch? It might be useful to identify similar-yet-different behaviors in your workplace that lend themselves to description errors.

Loss-of-activation errors are commonly referred to as "forgetting." You walk into a room and forget what you're looking for. That's because the cue or activator that sent you into the room was lost or forgotten. This happens whenever you start an activity with a clear goal, but then lose sight of it as you continue the task. Performance can subsequently slip. We can prevent this by adding specific behavior-based activators--signs, goal-setting discussions, verbal reminders, and friendly hand gestures--to guide performance.

Mode errors are probable whenever we face a task involving multiple options, or modes of operation. How many errors have you made at the keyboard of a computer by hitting the wrong key? These slips are common when equipment is designed with a greater variety of functions than the number of controls. How many people can operate a VCR, for instance? This type of slip is essentially one of execution. But these errors often involve memory and interpreting information. Equipment design is certainly important here, along with proper training and behavior-based activators.

Whether we're talking about slips, mistakes, or calculated risks, the only way we can reduce their frequency is through open and frequent discussions. By revealing our own slips and mistakes in group meetings, we raise awareness of these errors and motivate others to be honest and caring. Then with a proper behavior-based observation and feedback system, it's possible to anticipate and prevent the errors of our ways, and so prevent personal injury.