Sampling Methods and Sampling Bias

Why do we randomly select our samples?

• for control

• reduce bias

• so we don't get the same answers from everyone

• to eliminate confounding results

Disneyland often surveys its guests as they exit a restaurant during their visit. The surveyor stands at the restaurant exit, counts the number of people leaving, and surveys every 25th guest.
This is a form of:

• Simple Random Sample

• Stratified Random Sample

• Voluntary Response

• Systematic Random Sampling

A teacher wants to know the average time spent doing homework by the students in her class of 20 girls and 5 boys.
She picks the student in every 5th seat.

• Simple Random

• Systematic Random

• voluntary response

• convenience

Which of the following is TRUE?

• In a multi-stage random sample, all individuals and all subsets of the sample size have an equal chance of being selected.

• In a stratified random sample, all individuals and all subsets of the sample size have an equal chance of being selected.

• In a cluster random sample, all individuals and all subsets of the sample size have an equal chance of being selected.

• In a simple random sample, all individuals and all subsets of the sample size have an equal chance of being selected.

A student wants to know which type of pizza the students at his high school prefer. Which option would give an unbiased sample?

• Asking all the students in the hot lunch line.

• Asking 10 students from each homeroom

• Asking 100 random students, chosen by drawing names from a hat

• Asking all the 10th graders

Tanya wants to know the percent of people likely to attend the upcoming musical at school. She asks each person in the musical how many people they know who are coming to make a prediction. Why is this sample biased?

• Drama students are more likely to lie.

• Musicals are better attended than plays.

• The drama teacher was not asked.

• The sample is not random and not representative of the entire school population.

Answer explanation

The sample is not random and not representative of the entire school population, as it only includes people involved in the musical, leading to bias.

In order to estimate the proportion of students that text while driving, a school administrator selects a simple random sample of students from a list of all students at the school who have parking permits. The students are called to the office, one at a time. The administrator asks each student, “Do you text while driving, even though you are not supposed to?” Based on the survey, the administrator estimates that only 2% of students with parking passes text while driving. What potential bias is present in the design of this survey and what is the likely direction of the bias?

• The sample proportion is likely an underestimate of the population proportion due to response bias.

• The sample proportion is likely an underestimate of the population proportion due to undercoverage.

• The sample proportion is likely an underestimate of the population proportion due to nonresponse.

• The sample proportion is likely an overestimate of the population proportion due to response bias.

• The sample proportion is likely an overestimate of the population proportion due to undercoverage.

The School Dance Committee conducts a survey to find what type of music students would like to hear at the next dance. Which sampling method is least likely to result in a biased sample?

• Call the top 20% of the senior class. 

• Interview every 10^th student as they enter the school.

• Ask every 5^th person leaving a school jazz band concert.

• Set up a hip-hop only website where students can list their 3 favorite songs if they open up the link.

Farmer Joe's apple tree farm is set up in 100 rows.  He counts the number of apples produced on every 10th row to estimate the number apples produced on the whole farm.  This is _____________ sampling.  

• Random

• Stratified

• Voluntary-Response

• Systematic

Assign each car in a dealership a number and then use a random-number table to select the cars to be inspected. 

• systematic

• random sample

• convenience

• volunteer response