AP PSYCH 5.10 Psychometric Principles and Intelligence Testing

Measuring Intelligence

• Real intelligence tests need to have at least three traits
  • Standardization, or what an individual’s score is compared against
  • Reliability, the stability of the score over time
  • Validity, the ability of a test to measure what is intended

Standardization

• Standardization starts with giving many sample pretests to many people before the test is administered officially
• From those pretests, we can see the number of answers people get right
• A pattern will hopefully start to develop
  • Few people get most questions right
  • Most people get some questions right
  • Few people get most questions right
• Tests can be designed with different intentions in mind so this may look a little different
  • An test designed to be extremely hard will want to see most people doing poorly
  • A test designed to be very easy will want most people to get many answers right

Reliability

• If you take an intelligence test, then take a different version of the same test, you should get a similar score
  • If the same person gets wildly different scores on a test meant to be the same difficulty, it is not reliable
• A good test must correlate with another version of the test to be reliable
• The split-in-half method helps to ensure testing correlation
  • If a tester does better one one part of a tests than another part, the test is not correlated with itself
• The higher the self-correlation, the higher the reliability

Validity

• Validity is the most important issue in the formation of a test
  • Just because a test is reliable does not mean that it is valid
  • A broken scale might be reliable-- It gives the same weight every time-- But it is not valid
• Validity means to measure what is intended

Content Validity

• The extent to which a test samples the behavior that is of interest
• What you think of when thinking of validity

Construct Validity

• Similar to operationalization
• How well an abstract idea is translated into something measurable

Criterion Validity

• Correlation to an outside measure
• If a test claims someone is a genius, but they can’t tell left from right, there might not be criterion validity

Predictive Validity

• The success with which a test predicts the behavior it is designed to predict
• Assessed by computing the correlation between test scores and the criterion behavior
• The SAT has had many problems with predictive validity
  • For a long time, it was a horrible measure if you would actually do well if college or not
  • There was a period of time where no colleges accepted it because its predictive validity was so distorted
  • The SAT has undergone many edits to improve this metric

Scores on The Normal Curve

• Remember that the normal curve is a bell shaped curve, an ideal distribution of scores
• IQ scores fall into a normal curve
  • Few people get most questions right
  • Most people get some questions right
  • Few people get most questions right
• This pattern is standard
• Not all scores are average, some deviate from the standard
• 100 is the average score
  • 85 to 100 or 100 to 115 is one standard deviation away
  • A standard deviation is 15 points
• 68% of people fall within one standard deviation of 100 (85-115)
• 95% of people fall within two standard deviations (70-130)
• Beyond two deviations is unusual
  • Having an IQ score below 70 is considered an intellectual disability
  • Having an IQ above 130 is considered gifted