Surveys/ExperimentsObservation

2 sample project instructions

Avoid Bias Results

• What makes a sample bad?– Voluntary Response Sample• Biased towards those with strong opinions

Avoid Bias Results

• What makes a sample bad?– Voluntary Response Sample• Biased towards those with strong opinions• What would you be more likely to respond to:

– Raise the license age to 25 and revoke current licenses from younger drivers

Avoid Bias Results

• What makes a sample bad?– Voluntary Response Sample• Biased towards those with strong opinions• What would you be more likely to respond to:

– Raise the license age to 25 and revoke current licenses from younger drivers

– Change school dress code policy

Avoid Bias Results

• What makes a sample bad?– Convenience Sample

Avoid Bias Results

• What makes a sample bad?– Convenience Sample• Heights of the first person in each row

How can I obtain non biased results?

• Good sampling methods– Simple random sample• Lottery drawing

– Systematic • Every 10th person in an alphabetical list

– Cluster• Survey 2 freshman HR and 2 senior HR

Example

• Sample Letter to HR teacher:Dear Senior Homeroom Teacher,

Our Probability and Statistics class is collecting research for a statistical study. It is important that all students fill out the attached survey so that I can obtain accurate results. Please encourage your students to complete the survey honestly and accurately. Thank you for your time. I will be stopping by during 3rd period on Friday to pick up the completed surveys.

Sincerely,

Probability and Statistics Survey

Dear Student,Our Probability and Statistics class is collecting research for a statistical study. Please complete the following questions honestly and accurately. All responses are anonymous.

• How many times do you eat in a day? _____• Circle one: I am a male / female