Chapter 3:
Categorical Variable- Ordinal or Nominal
Ordinal: the levels of categories have some hierarchy to them: E.G. Class
standing (fr, so, jr, sr), level of education (HS, assoc., bach., masters, doct.)
Nominal: no order. E.G. Political party-> Dem. Rep. Other
Quantitative Variable. - Continuous or Discrete
Continuous: variable that are measured E.G. height, age, (don’t be confused
by the whole number)
Discrete: counted. E.G. # students in class, pages in a book.
Eye color-> Categorical, Nominal
Weight-> Quant. Continuous
Number of students in class-> Quant. Discrete
Gender-> Categorical Nominal
Course Letter Grade-> Categorical Ordinal
Problems with surveys.
Deliberate bias: the question wording biases, or influences how someone respond
 If you saw someone cheating would you report it?
 If you found someone cheating would you squeal and tell? (Deliberate bias)
“Desire to please” respondents provide answers to survey that they feel are best.
Leads to a response bias.
 Would you vote a person president if they were female and/or black?
The problem with this question is I asked the uninformed
 Which of the following courses do you think is the most difficult?
a. Simple Linear regression
b. Multiple Linear Regression
c. Logistic Regression
d. Regression in the 4th Dimension (doesn’t exist) (sounds hard)
The problem is the Question order
 How happy are you with your life in general? (1 to 10)
 How often do you go on a date? (amount of time per month)
I calculated two correlations: Split the class up and asked them the questions in
different order.
For Happy then Date-> -0.016
For Date then Happy-> 0.276
Difference between Confidential and Anonymous
Confidential: Intended to be kept secret. Can leek out.
Anonymous: Person not identified. No one will ever know.
Open-ended Question: Invoke some written response.
Closed Questions: Given a list of questions from which to choose.
Trick In Advertising (combines raise or same)
September 11-16 Quinnipiac Poll
If McCain elected, 88% believe taxes stay the same or increase.
If Obama elected, 81% believe taxes stay the same or increase.
When broken down,
McCain, 31% raise, 57% same
Obama, 49% raise, 32% same
Three concepts related to measurements.
1. Validity: does it measure what it is supposed to measure?
2. Reliability: would repeat measurements provide similar response of
3. Bias: is there a systematic prejudice in repeated measurements?
Your watch continually runs 5 minutes fast.
Valid? Yes, watch is to tell time and it is .
Reliable? Yes, reports the same time.
Bias? Yes, always 5 minutes fast.
What should be the goal of Exam 3? To asses your understanding of material to date.
What if I accidentally used my stat 501 exam for your exam 3?
Would the Exam be valid? No, does not measure what it is suppose to
measure, that is your understanding in Stat 100.
Is Exam reliable? Yes, as repeated deliveries of wrong exam result in similar
Is Exam bias? No,
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