Chapter 1
Psychological Science
Statistical Reasoning
Statistical Reasoning
Percentage
still functioning
after 10 years
100%
99
98
97
96
95
Our Brand Brand Brand
Brand
X
Y
Z
Brand of truck
Statistical Reasoning
Percentage
still functioning
after 10 years
100%
90
80
70
60
50
40
30
20
10
0
Our Brand
Brand
X
Brand Brand
Y
Z
Brand of truck
Statistical Reasoning

Mode


the most frequently occurring score in a
distribution
Mean

the arithmetic average of a distribution
 obtained by adding the scores and then dividing
by the number of scores

Median

the middle score in a distribution
 half the scores are above it and half are below it
Statistical Reasoning
A Skewed Distribution
15 20 25 30 35 40 45 50
90
475
70
Mode Median
One Family
Mean
Income per family in thousands of dollars
710
Statistical Reasoning

Range


Standard Deviation


the difference between the highest and lowest
scores in a distribution
a computed measure of how much scores vary
around the mean
Statistical Significance

a statistical statement of how likely it is that an
obtained result occurred by chance
Since 9% said that Nader was the only
candidate worth voting for, one would have
expected
to getstatistic
at leastbecause
9% of the
vote in
There
was him
a biased
the
the 2000
election.
He only
got from
aboutthe
3%. What
sample
wasn't
randomly
drawn
happened? A disproportionate number of
population.
Nader supporters participated in the poll in
order to make him appear more viable as a
candidate.
Solution:
The airlines
 Can weNo.
conclude
that
that
had the
most
United,
American,
and
complaints also had the
Delta are the worst
most passengers.
airlines and Alaska,
Southwest, and
Continental are the
best?
Solution:
This clipping
from USin
The difference
the
abuse
rates
probably
News
and
World
stems
from
Report
ondifferent
1/29/01
definitions for abuse in the
suggests that
various states. For example,
Alaskans
are terrible
Alaska
(the "worst"
state)
parents.
Is this
says
that a child
is true?
abused if
his or her health or welfare is
harmed or
threatened. Pennsylvania
(the "best" state) defines it as
a recent act or failure to act.
Solution:
No. Drunk
drivers
have a fatality
 Can we conclude
risk 7.66 times the
from
the non-drunk
following
norm,
while
drivers
havethat
a risk
diagram
it's safer
only about .6 of the
to drive
norm.
Onlywhile
a veryunder
small
thepercentage
influence?of
drivers in New York
City drive while under
the influence, but they
account for a
disproportionate
number of accidents.
Solution:
The following
No. As the
following
graph
shows,
the
statistics
suggest
that
reason
16-year-old
16-year-olds
areand
safer
octogenarians appear to
drivers than people in
be safe drivers is that they
theirdrive
twenties,
don't
nearly and
as much
octogenarians
asthat
people
in other age
are very safe. Is this
groups.
true?