Health-care choices with irreversible consequences, like having major surgery, submitting to aggressive chemotherapy or changing doctors during a serious illness are not matters to be decided with a coin toss. And the uncertainties attached to getting a divorce or retiring early from a secure job can cause the bravest person to freeze.

But not everyone is daunted by decisions. For example: Last year, Rex V. Brown's surgeon recommended against a hip replacement to treat his arthritis. Most might assume that, on hearing this good news, Brown, 55, heaved a sigh of relief and went about his business. Well, that's exactly what he did. But Brown's business just happens to be decision making, and he felt duty-bound to call his own bluff.

A logician, Brown took his dilemma to Langston Hughes Intermediate School in Reston where, under a research grant from the National Institute of Child Health and Human Development, he and mathematical statistician Kathryn Laskey teach a basic course for seventh and eighth-graders in logical decision making: Going Through the GOOP (goals, options, outcomes and probabilities).

The students analyzed his case using an arithmetical procedure. They assigned values to the possible outcomes of Brown's having or not having the hip operation and rated them -- using weights on a balance-beam scale -- as to likelihood and desirability. The most likely and desirable outcomes were assigned the heaviest weights, and the side that weighed the most indicated the the preferred decision.

At the end of the course, Brown took a vote. "Of course," he said, "I wouldn't have gone along with their recommendation if my own rational judgment and intuition had not coincided." That afternoon, he announced his decision to his surgeon: hip replacement. Brown explained the analysis, which balanced the facts of the case with value judgments, and asked for his doctor's comments. At the end of their conversation, the surgeon agreed that it was a sensible decision.

Brown had the surgery in June. Is he happy with his decision? "Oh, yes," he said. "It has worked just fine." He is now free of arthritic pain; his renewed flexibility made the dreaded decision-making worthwhile.

The secret of Brown's success lies in his realization that sound decision making cannot be rushed. This is particularly true when the decision maker is under stress. Stress and worry about the unknown complicate an already difficult process. Getting a diagnosis of cancer, oncologists say, can be emotionally paralyzing.

Yet many patients under stress feel pressured to narrow their options and to make a quick decision, although the cancer may have been there for decades. That's the worst thing to do, say professional decision makers. The logical course is to think of new options and to take time to think the problem through.

If a patient has cancer, for example, this might mean getting a second or third opinion, seeking state-of-the-art tests to learn whether a recurrence is likely and weighing treatment options in light of the patient's values.

Without skills in logical thinking, people fall prey to fallacies that can lead to less than ideal choices. Among the most common faults, says psychologist Jonathan Baron of the University of Pennsylvania, are:

Favoring the status quo. Wanting to play it safe, people won't risk leaving an unsatisfying job, career, marriage or doctor for a new, uncertain situation, even though they are under constant stress. Research psychologists Daniel Kahneman and Amos Tversky call this tendency to hang on to what you've got, rather than chance a gain, "loss aversion."

The "sunk-cost" effect ("throwing good money after bad"). Having invested time and money in a relationship, business venture or therapy, a person hangs on to a failing affair, marriage, sinking company or ineffective therapist. The time and money are already "over the dam and irrelevant to the real issue."

Shortsightedness. We overemphasize the immediate present and ignore long-range goals. For excitement and the pleasure of a clandestine sexual liaison, a drug high, a gourmet dessert, a person risks losing a stable marriage or public office or blows a diet.

Neglect of probability. Some assume that improbable events -- getting hooked, getting a sexually transmitted disease, getting caught -- won't happen. We also forget that choices set precedents for later choices, and probabilities add up. Riding once without a seatbelt, for example, is unlikely to kill you, but if it sets a precedent, chances of injury soar after hundreds of rides.

"My-side" bias. We defend our beliefs in an attempt to convince ourselves that we were right all along. If we hate exercise, we use reports of sports injuries to bolster our couch-potato stance.

Singlemindedness. We act as if our decisions have a single goal -- ending a bad marriage or leaving a dead-end job or losing weight -- while ignoring other relevant goals -- raising our children properly or providing a comfortable living for our family.

Such fallacies abound in everyday life, says Baron. "Even the most prestigious professions are vulnerable. Researchers have found that physicians and nurses are subject to the same sorts of defects in reasoning, which often lead to misdiagnosis and the failure to give optimal treatments."

Brown, a former professor at Harvard and at Carnegie-Mellon University, a major center for decision science, and his fellow decision analysts are not alone in urging others to get "a minimal kit of tools" for making sound decisions. At George Washington University, Robert Paul Churchill relates his course in logic to everyday personal problems. Students bring in current dilemmas and try to untangle confused thinking in class discussions and during long, after-hours, one-on-one chats.

If indecisiveness is chronic, says Lawrence Dalton of the Cognitive Therapy Center in Chevy Chase, it may be a sign of anxiety or depression. "Sitting on the fence is one of the hallmarks of depression. Look for clues, such as feeling less happy than normal or not sleeping well or comments by friends on your different mood. These are real red flags that you should share your problems with others.

"Indecisiveness happens a lot to two other major groups of people: The perfectionists who stall while they evaluate every advantage and disadvantage beyond a reasonable time and those who lack self-esteem and have little confidence in their own judgment. They'd rather leave all treatment choices up to their doctor. With guidance," Dalton said, "they could learn to be more self-reliant."

What if all the facts point to "right choice," and your gut feeling still says "no," so you stall? "If the two differ," said Brown, "chances are your intuition is closer."

In some cases, specialists say, not making a decision is a decision, and the decision is "no."

Barbara McGarry Peters is a freelance writer in Alexandria.

(Goals, Options, Outcomes and Probabilities)

Here's how Reston logician Rex V. Brown's students employed logic to make a decision about whether he should have a hip replacement.

Goals. Relief of pain from an arthritic hip, a return to regular exercise, more flexibility and independence in movement.

Options. 1. Operate soon.

2. Wait until hip gets worse.

Outcomes. 1. Having the operation soon would upset Brown's professional and personal plans. In addition to the slight risk of death, there would be pain resulting from the surgery, which would cost $5,000.

Furthermore, there was the chance that the surgery would have to be redone eventually -- Brown was 55 -- or that the operation might fail or that Brown's insurance might not cover the cost.

2. Postponing surgery would delay all risks indefinitely. It was possible that Brown could die before the future operation. But without surgery, Brown's exercise, already reduced drastically, would have to be further limited. And Brown's pain, while not now severe, would worsen. Brown also considered that perhaps less severe treatment might become available during the next several years.

Probabilities. When the probabilities of all the consequences had been weighed and Brown's values figured in, most students considered the operation the preferred option, as he did.

Brown had the operation. -- Barbara McGarry Peters