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Week03%20-%20Descriptive%20Statistics%20%28Sec010%29

# Week03%20-%20Descriptive%20Statistics%20%28Sec010%29 -...

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Descriptive Statistics Pyeong Whan Cho September 26 th , 2011 General Psychology I Lab 010 9/26/2011 1 PSYC 1100 / Lab 010 / Week 3

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Overview Quiz 1 (5 mins) Measurement & Scales Population & Sample Descriptive Statistics Central tendency Measure of Variability Assignment 1 9/26/2011 PSYC 1100 / Lab 010 / Week 3 2
MEASUREMENTS AND SCALES 9/26/2011 PSYC 1100 / Lab 010 / Week 3 3

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What is Measurement? Measurement is the foundation of any scientific investigation. Measurement is the assignment of numbers of objects . E.g., We are measuring computer skill by assigning a number (1-5) to an object (a person). E.g., We are measuring heights by assigning a number (a real number) to a person. 9/26/2011 PSYC 1100 / Lab 010 / Week 3 4
Four Types of Measurement Scales Nominal scale It simply labels objects. Numbers have no other meanings. Gender is a nominal scale. Female = 1, Male = 2 Favorite color is also a nominal scale. Blue = 1, Red = 2, 9/26/2011 PSYC 1100 / Lab 010 / Week 3 5

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Four Types of Measurement Scales Ordinal scale Numbers are used to place objects in order . BUT, no information regarding the differences between points on the scale. E.g., Computer skill We know a person assigned to “2” is more skillful than a person assigned to “1”. But we don’t know if the skill difference between “1” and “2” is the same as the difference between “2” and “3”. 9/26/2011 PSYC 1100 / Lab 010 / Week 3 6
Four Types of Measurement Scales Interval scale An interval scale is a scale on which equal intervals between objects, represent equal differences . The interval difference is meaningful. Arbitrary zero point . E.g., Fahrenheit scale The difference between 10 and 20 degrees is the same as the difference between 80 and 90 degrees. But 80 degrees is not twice as hot as 40 degrees. 9/26/2011 PSYC 1100 / Lab 010 / Week 3 7

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Four Types of Measurement Scales Ratio scale Has a true zero point . Ratios are meaningful. E.g., Physical time (Age, RT), length (Height) We can say that 20 seconds is twice as long as 10 seconds. 9/26/2011 PSYC 1100 / Lab 010 / Week 3 8
Remember! The underlying construct or variable being measured defines the scale of measurement, not the numbers themselves.

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