Measurements, Mistakes and Misunderstandings

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Chapter 3

• Measurements, Mistakes and Misunderstandings

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Thought Questions
2, page 31
You and a friend are each doing a survey to see
if there is a relationship between height and
happiness. You both attempt to measure the
height and happiness of the same 100 people.
Are you more likely to agree on your measurement
of height or on your measurement of happiness?
Explain, discussing how you would measure each
characteristic.
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Thought Questions
3, page 31
A newsletter distributed by a politician to his
constituents gave the results of a nationwide
survey on Americans attitudes about a variety of
educational issues. One of the questions asked
was, Should your legislature adopt a policy to
assist children in failing schools to opt out of
that school and attend an alternative
school--public, private, or parochial--of the
parents choosing? From the wording of this
question, can you speculate on what answer was
desired? Explain.
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Thought Questions
4, page 31
You are at a swimming pool with a friend and
become curious about the width of the pool. Your
friend has a 12-inch ruler and sets about
measuring the width. He reports to you that the
width is 15.771 feet. Do you believe the
measurement? What is the problem?
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Thought Questions
4, page 31
You are at a swimming pool with a friend and
become curious about the width of the pool. Your
friend has a 12-inch ruler and sets about
measuring the width. He reports to you that the
width is 15.771 feet. Do you believe the
measurement? What is the problem?
15.771 ft 15 ft, 9.25 in
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Thought Questions
5, page 31
If you were to have your intelligence, or IQ,
measured twice using a standard IQ test, do you
think it would be exactly the same measurement
both times? What factors might account for any
changes?
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Variable

• Categorical
• Measurement
• Discrete
• Continuous

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Case Study
The Effect of Hypnosis on the Immune System

• Easy or difficult to achieve hypnotic trance
• Group assignment
• Pre-study white blood cell count
• Post-study white blood cell count

categorical measurement discrete
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Case Study
Weight Gain Spells Heart Risk for Women

• Age (in 1976)
• Weight in 1976
• Weight at age 18
• Incidence of coronary heart disease
• Other smoking, family history, menopausal
  status, post-menopausal hormone use.

measurement continuous
categorical
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The Pitfalls of Asking Survey Questions

• Deliberate bias
• Unintentional bias
• Desire to please
• Asking the uninformed
• Unnecessary complexity
• Ordering of questions
• Confidentiality and anonymity

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Deliberate Bias

• If you found a wallet with 20 in it, would you
  return the money?
• If you found a wallet with 20 in it, would you
  do the right thing and return the money?

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Unintentional Bias

• I have taught several students over the past few
  years.
• How many students do you think I have taught?
• How many years am I referring to?
• Over the past few days, how many servings of
  fruit have you eaten?
• How many days are you considering?
• What constitutes a serving?

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Desire to Please

• Is your instructor doing a good job presenting
  the course material in a clear and interesting
  way?
• Yes
• No

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Asking the UninformedA Case Study Washington
Post National Weekly Edition (April 10-16, 1995,
p. 36)

• A 1978 poll done in Cincinnati asked people
  whether they favored or opposed repealing the
  1975 Public Affairs Act.
• There was no such act!
• About one third of those asked expressed an
  opinion about it.

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Unnecessary Complexity

• Do you sometimes find that you have arguments
  with your family members and co-workers?
• Arguments with family members
• Arguments with co-workers

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Ordering of Questions

• How often do you normally go out on a date?
  about ___ times a month.
• How happy are you with life in general.
• Strong association between these two questions.
• Now, considering what you just told me about
  dating, how happy

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Ordering of Questions

• How happy are you with life in general.
• How often do you normally go out on a date?
  about ___ times a month.
• No strong association between these two questions.

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Confidentiality and Anonymity

• Confidential answer
• respondent is known, but the information is a
  secret
• Anonymous answer
• the respondent is not known, or cannot be linked
  to his/her response

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Other Terms to Study

• Bias
• Variability
• Natural Variability

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Bias, Sources of Variability

• Bias if standing on elevated surface (s
  will be too high)
• Heights vary from person to person.
• People are naturally different.
• Some variation due to natural causes.
• Some variation due to fundamental differences in
  groups.

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Key Concepts

• Often it is difficult to precisely define and
  measure something.
• Its all in the wording the pitfalls
• Two main types of variables
• Bias and variability