1. Surveys/Experiments Observation 2 sample project instructions

2. Avoid Bias Results What makes a sample bad? – Voluntary Response Sample Biased towards those with strong opinions

3. 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

4. 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

5. Avoid Bias Results What makes a sample bad? – Convenience Sample

6. Avoid Bias Results What makes a sample bad? – Convenience Sample Heights of the first person in each row

7. How can I obtain non biased results? Good sampling methods – Simple random sample Lottery drawing – Systematic Every 10 th person in an alphabetical list – Cluster Survey 2 freshman HR and 2 senior HR

8. 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 3 rd period on Friday to pick up the completed surveys. Sincerely,

9. 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