COMM 88 Lecture Notes - Lecture 6: Semantic Differential
Comm 88 Lecture 6
April 19, 2018
Measurement - Operationalizing Variables (both IVs and DVs) cont.
•Levels of measurement
•Nominal (categorical/discrete): variable is measured merely with different categories
•Ex: gender (M/F), ethnicity, yes/no Qs, TV use (Hi/Lo), persuasive appeal (humor/non-)
•For comparing differences…
•Between manipulated IV conditions in experiments
•Between existing IV groups in surveys
•Ordinal: variable is measured with rank ordered categories
•Ex: rank top five favorite TV shows, most to least important political issues
•Interval: variable is measured with successive points on a scale with equal intervals
•Ex: measure of attitude about parenting: parents should talk openly with their children
about sex
•Ratio: interval measurement with a true, absolute, zero point
•Ex: time in hours, weight in lbs, age in years, etc.
•Ex: test scores (if from 0 possible)
•Allows you to make ratios, zero gives you an anchor (twice as much)
•Interval and ratio measures are both “continuous” variables
•Allow you to capture more variation
•Can always collapse to categories later, if need be
•Allow you to compare means (avg’s on DV)
•Allow you to test continuous relationships
•Positive: the more X, the more Y, negative: the more X, the less Y
Using Questionnaire Items as Measures
•Common for IVs and DVs in surveys
•Common for Das in experiments (IV is a manipulation into groups)
•Open-ended: respondents give their own answers to Qs
•Close-ended: respondents select from list of choices
•Choices must be mutually exclusive
•Choices must be exhaustive
•Some close-ended formats
•Likert-type items: respondents indicate their agreement with a particular statement
•Ex: I feel uncomfortable when people are arguing, strongly disagree, strongly agree
•Other response options also possible: oppose/favor, not at all/very much, almost never/
almost always
•Semantic differential: respondents make ratings between 2 opposite (bipolar) adjectives
(phrases)
•Ex: this candidate seems: honest __:__:__:__:__:__:__ dishonest
•Composite measures - use multiple items combined to measure one variable (i.e., create an
index/scale)
•Ex: candidate credibility honest, trustworthy, sincere, for each subject, add together (on
average) scores on all three items into an overall credibility score
How Good Is your Measurement? Reliability and Validity
•Reliability of measurement
•Does your measure (of the variable) have consistency?
