There's a big problem with Brendan Dassey's low IQ defence on Making a Murderer

Brendan dasseyAP ImagesThen-16-year-old Brendan Dassey was convicted of helping Steven Avery in murder.

The Netflix docuseries “Making a Murderer” follows the story of Steven Avery, a Wisconsin man who spent 18 years in prison for a crime he didn’t commit, only to be convicted in the 2005 murder of photographer Teresa Halbach.

It also follows the trial and conviction of Avery’s then-16-year-old nephew Brendan Dassey as an accomplice.

According to court documents, Dassey was convicted of first-degree intentional homicide, mutilation of a corpse, and second-degree sexual assault.

As depicted on the show, the conviction appeared to be largely based off of a confession Dassey gave to police, which his defence attorneys argue was coerced. The attorneys repeatedly make the case that Dassey was susceptible to police pressure to confess because he had a low IQ.

IQ scores have been linked with many things, including a person’s school and job performance, income, social status, and risk of death.

But there’s a lot of debate in the scientific community about what a high or low IQ actually means.

What IQ tests really measure

The term “IQ” test, which stands for intelligence quotient, was developed by the German psychologist William Stern in the early 1900s. The test usually consists of a standard set of questions designed to measure human intelligence in logic, maths, and verbal comprehension.

The average IQ score in each age group is defined as 100, so in a typical population, two-thirds of people score between 85 and 115. By comparison, the show reveals that Brendan Dassey has an IQ of 73 (and a verbal IQ of 69).

In some states, an IQ of 70 or below is used as the cutoff for intellectual disability. But in 1978, the Supreme Court overturned the death sentence of a defendant who was found guilty of rape and murder who had an IQ of 71, arguing against a strict cutoff.

One of the most widely used IQ tests is the Wechsler Intelligence Scale, which comes in adult and children’s forms. The test measures two types of intelligence: verbal intelligence (things like vocabulary and comprehension) and performance intelligence (like pattern recognition and picture completion).

Another commonly used test is the Stanford-Binet Intelligence Scales, which measure a combination of five factors, including fluid reasoning, knowledge, quantitative reasoning, visual-spatial processing, and working memory. The test is used to diagnose developmental or intellectual problems in young children.

But some experts argue that IQ tests measure specific types of intelligence at the expense of others.

A narrow definition of intelligence

In the case of Brendan Dassey, Richard Leo, an expert on coercion and false confessions, testified in a 2010 hearing for Dassey’s defence that the teen was coerced into confessing his involvement in Halbach’s rape and murder, without understanding the consequences. But an IQ test alone wouldn’t tell you that.

In his 1983 book “Frames of Mind: The Theory of Multiple Intelligences,” developmental psychologist Howard Gardner described eight different kinds of intelligence: musical — rhythmic, visual — spatial, verbal — linguistic, logical — mathematical, bodily — kinesthetic, interpersonal, intrapersonal, and naturalistic.

By Gardner’s definition, IQ tests only measure verbal-linguistic, logical-mathematical, and some types of spatial intelligence. It doesn’t necessarily predict poor intra-personal intelligence — another term for self-awareness and introspection — the kind of intelligence you might expect to explain why Dassey was susceptible to coercion by the police.

Still, that doesn’t mean we should get rid of IQ tests completely, Illinois State psychologist W. Joel Schneider said in an interview with psychologist and science writer Scott Barry Kaufman.

“IQ tests, error-ridden as they are, peel back a layer or two of uncertainty about what people are capable of,” Schneider said.

NOW WATCH: The lawyer from ‘Making A Murderer’ describes what’s wrong with America’s criminal justice system

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