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The Benefits
and Risks ofChapter 1
s ng tat st cs
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Th h i n 1
A recent news a er article concluded
thatsmoking marijuana at least three
in college.How do you think the researchers came
to this conclusion? Do ou believe it?
Is there a more reasonable conclusion?
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Th h i n 2Theor : On avera e, men have lower
resting pulse rates than women do.
or disprove that? Would it be sufficient
of each sex? Two members of each sex?What information about mens andwomens pulse rates would help youdecide how man eo le to measure?
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Th h i n
Su ose ou were to learn that the lar e
state university in a particular state
went on to become millionaires than any of
.
Would that be a fair comparison?
ow s ou t e num ers e presentein order to make it a fair comparison?
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Th h i n 4In its March 35, 1995 issue, USA Weekend
magazine asked readers to return a surveywith a variety of questions about sex andviolence on television. Of 65,142 readers
who responded, 97% were very orsomew at concerne a out v o ence on(USA Weekend, 24 June 1995, p. 5).
about 97% of U.S. citizens are concernedabout violence on TV? Wh or wh not?
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1 1 i i
procedures and principles for
gaining and analyzing
information in order to helpeople make decisions when
ace w uncer a n y.
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Statistics in Your Own LifeWhich route to go to school,
class, work?Tr each a few timesThen choosebest one.
Sampling routes and comparing them
information to make a decision.
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Case Study 1.1: Heart or
ypo a amus
Hypothalamus plays role in emotion, yet most
people think about the heart. Psychologist LeeSalk studied role of heart in human relationships.
Observations:
,by the heart, on 40 out of 42 occasions.
of giving birth), 237 or 83% held babies
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Case Study 1.1: Heart or
ypo a amus
More Observations:
Out o 438 s oppers eav ng store w t onebag, exactly half carried bag on the left.
Denta pat ents as e to o a 5- nc a
while teeth worked on. Substantially more
Salks conjecture:
.
Must be survival value to having a newborn
placed close to sound of mothers heartbeat.
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Case Study 1.1: Heart or
ypo a amus
Controlled Experiment:
Baby nursery at NY City hospital. 1st rou of newborns: Continuous sound
of human heartbeat over loudspeaker.
2ndgroup of newborns: no sound played.Response: weight gain (or loss) after 4 days.
u :Infants treated to heartbeat sound gained
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more we g os ess an cr e ess.
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1.2 Detecting Patterns
and Relationships
Obvious or Not? Average man taller than average woman.
Taking aspirin helps prevent heart attacks.
More likel to bu blue eans in certain monthsthan others.
Men have lower restin ulse rates than women.
Listening to Mozart improves spatial reasoning.
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Statistical StudiesTo conduct a statistical study
1. Get a representative sample.
,
2. Get a large enough sample.
3. Decide whether the stud shouldbe an observational study or
a randomized ex eriment.
Example: Assess if men have lower
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.
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1. Get a representative sample.
Sample = those actually studied
=
sample was chosen
esearc ers wan o ex en resu s
beyond just the sample.For pulse rates:
Convenient sample = members of your class.
Not valid, e.g., if entire track team in class.Couldnt extend to other age groups.
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2. Get a large enough sample.
How large is large enough?
.
More variable within each grouplar er sam le needed to detect a difference.
For pulse rates: a men a ra e o an a women a ra e
of 75, then just need afew to see the difference.
rates ranged from 52 to 82, then would take
more measurements to see a difference.
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3. An observational Study
or Randomized Experiment?
Observational Study: merely observe thingsa out our samp e.
Randomized Experiment: randomly assignartici ants to one of various treatment
groups.
Sufficient to measure or observe both pulse
rates and ender of eo le in sam le.
To learn if aspirin helps prevent heart attacks,
a randomized experiment would be better.
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Case Study 1.2: Does Aspirin Prevent
eart ttac s
Physicians Health Study (1988)
5-year randomized experiment22,071 male h sicians 40 to 84 ears old .
Group 1: took ordinaryaspirin tablet
every other day. Group 2: tookplacebo (looked like aspirin
but no active ingredients).
Subjects did not know which group they
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.
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.Heart Attacks?
C o n d it i o n H ea r t A t ta c k N o H ea r t A t t a c k A t ta c k s p er 1 00 0A sp irin 1 0 4 1 0 ,93 3 9 .4 2P lacebo 189 10 ,845 17 .13
Results:
Heart attack rate in as irin rou onl 55% of ratein placebo group.
Randomization other factors, such as amount of
exerc se, expecte to e s m ar or ot groups. Subjects were male physicians. Results may not
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, .
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1.3 Dont Be Deceived By
Improper Use of Statistics
xamp e
Business Magazine sent 2000 questionnaires torea ers a ou epu can pr mary: rys erpresident Lee Iacocca vs. VP George Bush.
,Iacocca would beat Bush 54% to 47%.
people likely to vote: those who feel stronglyabout an issue most likely to respond.
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Improper Use of Statistics
Example 2
U.S. EPA study led to report that New Jerseyranked 22ndin its release of toxic chemicals.
Problem: wrong units ranking was based
on total pounds released. Using appropriate rate of pounds releasedper
s uare mile, New Jerse ranked 4th on the list.
Figures were misleading until adjusted for size.
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Improper Use of Statistics
Example 3
Article headline:Stud : Smokin Ma Lower Kids I s
Headline implication: a causal connection.
study (since experiment would be unethical).
ora : an t ma e causa connect onsfrom observational studies.
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Improper Use of StatisticsNew study confirms too much pot impairs brain
More evidence that chronic marijuana smoking impairs mental
ability: Researchers at the University of Iowa College of Medicine
say a test shows those who smoke seven or more marijuana joints
per week had lower math, verbal and memory scores than non-marijuana users. Scores were particularly reduced when marijuana
Example 4
users e a o n s smo e n e r ungs or onger per o s. SanFrancisco Examiner, 13 March 1993, p. D-1.
Headline implication: a causal connection.
Can concludethere is a relationshipbut
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.
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Case Study 1.3: A Mistaken Accusation
o eat ng
Two students accused of cheating on multiplex ue o w sper ng ur ng one
part and wrong answers often matched each other. Licensin board estimated odds of havin answers
as close as these two were < 1 in 10,000.
At trial, statistician showed agreement in this examwas no g er t an n ot er exams.
Key: two students were husband and wife, both.
they were just guessing. Instead, common mistakeswere often the right answers for India background.
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Whispering had to do with status of sick child.
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1.4 Summary and Conclusions
using statistical methods.
You need to know how data were collected,, .
Over the next several chapters, you will
ecome an e uca e consumer o s a s cainformation.
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Tutorial Questions
,
such as movies, sports events and concerts,
cousins to survive the next eight to nine
years, even w en e uca on an ncome are
taken into account, according to a survey by
t e n vers ty o mea n we en(American Health, April 1997, p.20).
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Tutorial Questions
.
randomized experiment? Explain.b. On the basis of the stud that was conducted can
we conclude that attending cultural events causes
people to be likely to live longer? Explain.c. The article continued No ones sure how Mel
Gibson and Mozart help health, but the activities
may enhance immunity or coping skills.Comment on the validity of this statement.
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