Measurement 2011, 9, 8

ExperimentQuasi-ExperimentSurvey Research goal If caffeine (IV) causes anxiety (DV)? If two naturally-occurring groups (fraternity/sorority group vs. students not in such organizations) are different in their alcohol consumption (DV)? If watching violent TV (IV) is related to displaying aggressive behavior (DV)? How to conduct? Assigning participants in to experimental or control conditions (manipulating the IV), and then measuring their anxiety level (DV) Comparing Greek to non- Greek (IV is the naturally- occurring groups), and measure their alcohol consumption (DV) Measuring amount of violent TV watched (IV), and measuring aggressive behavior displayed (DV) Similarities Comparing two conditions or groups IV: Groups Difference In experiment, researchers assign participants into either caffeine group or non-caffeine group, and compare their anxiety level; in quasi-experiment, researchers compare two naturally occurring groups (Greek vs. non-Greek) in their alcohol consumption. Difference In both experiment and quasi-experiment, researchers compare two groups. In a survey, there is no comparison. Researchers only work with one group. The researchers measure the amount of violent TV watched and aggressive behavior displayed on one group of participants, and study if there is any relationship between watching violent TV and aggressive behavior.

Today’s Topics  Scale of measurement*  Measurement reliability*  Measurement validity**

Measuring a Variable  Nominal Scale: Mutually exclusive categories without order –Political party: Democrat, Republican –Gender: Male, Female  Ordinal Scale: Categories with rank order –Social class: Upper, middle, lower –Education level: High school, college, graduate  Interval-Ratio Scale: the intervals between two consecutive categories are the same size –Temperature –Income arbitrary zero natural zero

Critical Thinking Question  What is the difference between measurement unit and unit of analysis?

Reliability  An indication of the consistency or stability of a measuring instrument –Free of random error  Question 1: You took an IQ test twice in one day. In the morning, you received a below-average score of 85. So took it again in the afternoon. This time, you received a above-average score of 120. What is the problem of the IQ test?  Question 2: I tend to be late because my watch is set 10 minutes behind. Is my watch reliable? What is the problem of the watch?

Validity (Accuracy)  Whether a measure is truthful or genuine –Free of random error: Same result over and over –Free of systematic bias: Accurate result –Measures what it is designed to measure  Need for Achievement scale

Lab 3 Recap  Scale of measurement –Nominal scale –Ordinal scale –Interval-ratio scale  Reliability: Free of random error  Validity / Accuracy: –Free of random error –Free of systematic bias –Measures what it is supposed to measure