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Chapter 9: Intelligence (2)

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PSYC 1002
Lorena Ruci

Lecture 5: Intelligence Measures of Variability  Standard deviation: numerical value that tells us how spread out the scores are about the mean o Take each score, subtract from mean, square it, add it, then take the difference from the mean, then the square root of that number is the variant  Major characteristics of bell curve: mean, median, and mode are the same  Properties: o Can never be negative o Sensitive to outliers (extreme score that greatly influence standard of deviation) o In some cases, it can be zero, i.e. when all the scores are the same Reliability and Validity  Reliability o No measurement error  Same person, same score o Test-retest reliability  Error: inability to have a measurement that is a perfect representation of the concept we’re trying to capture  In psychological testing, the score is a representation of the true score plus error (X = T + E)  Error is important because, in our measurements, we are constantly trying to get the score (X) closer to the true score (T)  Random Error: unpredictable; if you could predict it, you could control it  Random error always contaminates the true measurement  Reliability is the consistency of the scale o If a scale is reliable, it means that when we distribute that measure, it will give us similar or almost identical results o There is no scale with perfect reliability o In order to increase the reliability of a scale, we can limit the amount of error based on some variables Types of Errors (Reliability)  Time Sampling Error o Test-retest reliability: correlation of two scores o Testing math ability to one group in the morning, one in the afternoon, and one at night o More people are fatigued late at night  Item Sampling Error o Items are chosen for a scale, but some are unrelated to the concept you are trying to measure o E.g. measure spelling ability using long, scientific words to high school students, but most students wouldn’t recognize these words  Internal Consistency Error o Represents the extent to which the items on a scale measure the same thing o E.g. reverse scored questions to minimize this error, or questioned asked differently (I like driving, I have liked driving in the past, I hate automobiles; you can’t like driving but hate cars, so if you got a maximum score on all of them, then internal consistency is present)  Even if you try to control these types of error, random error is inevitable Validity  A test or measure does what it’s supposed to do  Has to do with the content of the test or measure, not so much with error  Criterion-Rela
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