Warm Up
The GMC teachers decide to get rid of pizza
for lunch. After a survey of all teachers,
counselors, and administrators, it was
overwhelmingly decided that pizza would
be replaced with broccoli w/ ranch
dressing.
What is your initial reaction? Why?
Warm Up Cont.
1. Who would be pleased with the results of the
survey? Why?
2. Who would not like the results of the survey? Why?
3. Who is the population?
4. What characteristic of this survey could we change
to make the situation fair?
5. What could we do to make the survey more fair or
accurate?
Early Lunch Example
After surveying 83 students in three
classes, 70% responded that girls
should be allowed to go to lunch ten
minutes early every day and boys will
continue to go at the regular time.
Early Lunch
1. Do you think this is an accurate (fair)
statistic? Why or Why not?
2. Based on the results, who would the
statistic be biased towards?
3. What could have made this
inaccurate (unfair)?
Early Lunch
4. Based on the results of the study
which three classes do you think the
sample population was made of?
What if I told you the 3 classes that
were surveyed were the girl’s gym class,
the home economics class, and teacher
cadets. Do the results make sense now?
Early Lunch
5. Who is the actual population?
6. Who would we include in our
sample survey that would produce
a more unbiased statistic?
Bias
Favor occurs in some way for some
part of the population.
What were the two types of sampling
that we considered biased?
Bias Samples
Data was obtained from LHS High School
using 582 students from the Freshman
class who carried backpacks.
The data pertains to the color of backpacks
the students carry to school (Black, Brown,
Red, Yellow, Green, Pink and Purple).
Example #1
The first sample of students that were
surveyed were the freshmen guys who had
4th period gym class.
Is this sample biased?
THINK PAIR SHARE
Example #2
The second sample of students that were
surveyed were the students in four Algebra
classes. 14 students were absent on the
day of the survey.
Is this sample biased?
THINK PAIR SHARE
Bias Samples
Eight citizens are asked their opinions
about when the New York City’s trash
should be collected.
Is this sample biased?
THINK PAIR SHARE
Bias Samples
There are fifteen boys and fifteen girls in a
math class. Each student’s name is placed
in a hat and the names are thoroughly
mixed. Seven names are drawn and all
names correspond to the boys in the class.
Is this sample biased?
THINK PAIR SHARE
Variability
Describes how spread out the values of the
sample statistic are with many samples.
A good sampling method has both low bias and low variability!
Example
Label each of the graphs as showing high or low
bias AND as showing high or low variability.
To Reduce
To reduce BIAS
Use random sampling. Begin with the
entire population and use SRS procedures.
To reduce VARIABILITY
Use a larger simple random sample.
Bias Examples
Which question is unbiased?
a)
b)
c)
d)
Do you think the mayor is doing a good job in
spite of his questionable character?
Does the school board have the right to
enforce a dress code?
Do you prefer daytime or evening television
programming?
Do you think the government should be
allowed to cut down trees willy-nilly to build a
new highway?
Bias Examples
Which question is biased?
a) Do you prefer daytime or evening
television programing?
b) Should there be a school dress code?
c) Do you prefer news or mindless sitcoms?
d) Do you think a new highway should be
built?
Exploring Bias
Under the following examples, determine
whether the survey sample is biased or
unbiased. Be prepared to explain your answers.
Survey Question: What is your favorite sport?
Sample is chosen from people attending a soccer
game.
Exploring Bias
Under the following examples, determine
whether the survey sample is biased or
unbiased. Be prepared to explain your answers.
Survey Question: Should more money be put
into athletic programs or music programs at
school?
Sample is chosen from students in the band
program.
Exploring Bias
Under the following examples, determine
whether the survey sample is biased or
unbiased. Be prepared to explain your answers.
Survey Question: What is your favorite vacation
destination?
Sample is chosen by asking every student in the
class
Exploring Bias
Under the following examples, determine
whether the survey sample is biased or
unbiased. Be prepared to explain your answers.
Survey Question: What is your favorite soft drink?
Sample is chosen by picking random names out
of a telephone book.
Homework
Worksheet
Due Wednesday!