If you could find out how you were going to die, would you want to know? For most people, the answer is likely "no" - unless you could do something about it.

From genetic screening for diseases to questions of infidelity, psychologists report that people's ability to control a situation's outcome can predict whether they choose ignorance or knowledge in potentially upsetting situations.

The comprehensive research, which helps explain why we're likelier to read about a missing local puppy than Third World genocide, was presented this month at the annual convention of the American Psychological Society.

James A. Shepperd, a University of Florida psychology professor, calls the phenomenon "calculated ignorance."

"It's the intentional avoidance of information that's important but unwelcome," says Shepperd, who over the past three years has been involved in about 30 studies on the subject.

"Kids, for example, want to avoid all sorts of information about their parents.

They don't want to know they've had sex, ever, or are in any way sexual."

In a graver example, Shepperd says studies show that between 13 and 55 per cent of people who get AIDS tests never return for the results. In other words, at least two million of the roughly 17 million Americans who were screened last year don't know whether they're infected.

Shepperd cites three primary motives for calculated ignorance: the potential for the news to spark unpleasant feelings, such as hearing that a loved one was unfaithful; the potential for the information to threaten a cherished selfview, such as considering oneself good-looking, lovable or healthy; and the potential for the news to compel an undesired reaction - say, learning that you have diabetes and being forced to swap cupcakes for carrot sticks.

"A big moderator is control," Shepperd says. "To the extent that I can control the outcome, or the progression, I'm much more interested in knowing. But if I can't, I'm likely to opt for ignorance because it may make me feel bad or obligate an unwanted action."

In one public health study, women with uncontrollable predictors of breast cancer were much likelier to avoid breast cancer screening results than women with controllable factors, such as poor diet.

In another study, students whose photos were rated for attractiveness by their university peers were later given the option to learn how their looks were assessed. Fully half declined.

The good news is that self-affirmation - that is, purposefully thinking about our value as people - shows promise as an intervention. For example, in an experiment in which individuals boosted themselves before being given the option of exposure to potentially upsetting news, calculated ignorance dropped from 55 per cent to just 16 per cent.

Asking people to contemplate the reasons they're evading knowledge also seems to work, with avoidance rates of that knowledge dropping from 55 to 28 per cent after such an exercise.

But Shepperd emphasizes that calculated ignorance isn't always a bad thing.

"Finding out someone else paid less for a product is just going to make me feel bad - particularly if I can't return it or do anything about it," he says.

"But if it's something like finding out if I have terminal cancer and could be dead in four months, then I need to get my affairs in order and knowing is useful."