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Professor of psychology Matthew Nock studies suicidal and self-injurious behavior: what
causes it, how to predict it, and how to prevent it.
As one way of assessing people’s risk of attempting suicide, Nock adapted two tests
that had previously been used for other purposes in psychology research.
The Implicit Association Test, or IAT, developed by Nock’s colleague Mahzarin Banaji, examines
thoughts people may not admit to, or may not even be aware of, by tracking subjects’
response times as they associate words with images or with other words.
Banaji had used the IAT to assess prejudice about race, sex, ethnicity, *** orientation,
and obesity. For example, subjects rapidly made the association between “good” and
pictures of European-American faces
and the association between “bad” and pictures of African-Americans.
They took longer to associate bad with the pictures of white people
and to associate good with the pictures of black people
—indicating latent prejudice, even though their attitudes, gauged with a questionnaire,
revealed no such preference.
On Matthew Nock’s version of the IAT
—designed to assess people’s risk of attempting suicide—subjects are asked to associate
suicide-related words or pictures with personally relevant words such as “self”
Their response time when making these pairings is compared to their response time as they
associate the suicide-related words and images with non-personally relevant words.
Using the test on children who had engaged in self-injurious behavior such as cutting
themselves, Nock found that the children who scored highest on the test, making the fastest
associations when pairing self and self-harm, were most likely to make a suicide attempt.
He obtained a similar finding with adults: those who made the more rapid associations
when pairing self and death/suicide were more likely to have made a recent suicide attempt.
Moreover, performance on this test also significantly predicted which suicide attempters went on
to make another attempt in the next six months.
Within the last five years, Banaji notes, “a great deal of evidence has mounted to
demonstrate that the IAT predicts real-world behavior.” She says Nock’s work with the
IAT “is a significant contribution to showing that a relatively mechanistic, computerized
test can predict how people behave—from hiring to evaluation of work, from medical
treatment to, now, predicting who is likely to commit suicide.”
The Stroop test has been used in psychology since the 1930s. On this test, a longer response
time is presumed to indicate that a person has already been thinking about something.
The test assesses attention by asking subjects to override their instantaneous reactions
and engage in higher-order thinking. For example, subjects might see the word “red” printed
in green ink.
Their first impulse is to read the word out loud; the test asks them to override this
impulse and name the ink color, green, instead.
In adapting the test for his purposes, Nock measured subjects’ response time as they
named the ink colors of suicide-related words such as suicide, dead, and funeral
and compared that response time to their speed in naming the ink colors of neutral words
such as paper, engine, and museum.
He found that for each millisecond of increased response time, came a 1 percent increase in
the odds that a subject would make a suicide attempt within the next six months. Nock explains
that the increased response time presumably means the subject was distracted by the suicide-related
words and prevented from naming the color as quickly.
Nock cautions that further experiments are needed—for instance, testing the predictive
ability of these tools with people who have not previously attempted suicide or been thinking
about suicide. But he believes these tests ultimately may have the potential for widespread
use in determining who is at risk of attempting suicide, and most urgently in need of treatment.