Warm UpThe 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 ExampleAfter 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 Lunch1. 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 Lunch4. 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 Lunch5. Who is the actual population?

6. Who would we include in our sample survey that would produce a more unbiased statistic?

BiasFavor occurs in some way for some part of the population.

What were the two types of sampling that we considered biased?

Bias SamplesData 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 #1The 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 #2The 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 SamplesEight citizens are asked their opinions about when the New York City’s trash should be collected.

Is this sample biased?

THINK PAIR SHARE

Bias SamplesThere 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

VariabilityDescribes how spread out the values of the sample statistic are with many samples.

A good sampling method has both low bias and low variability!

ExampleLabel each of the graphs as showing high or low bias AND as showing high or low variability.

To ReduceTo reduce BIASUse random sampling. Begin with the entire population and use SRS procedures.

To reduce VARIABILITYUse a larger simple random sample.

Bias ExamplesWhich question is unbiased?

a) Do you think the mayor is doing a good job in spite of his questionable character?

b) Does the school board have the right to enforce a dress code?

c) Do you prefer daytime or evening television programming?

d) Do you think the government should be allowed to cut down trees willy-nilly to build a new highway?

Bias ExamplesWhich 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 BiasUnder 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 BiasUnder 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 BiasUnder 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 BiasUnder 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.

HomeworkWorksheet

Due Wednesday!