1. Statistical Reasoning Intro to Probability and Statistics Mr. Spering – Room 113

2. 1.3 Types of Statistical Study Subjects – people or objects chosen for the sample Participants – when the subjects are people usually referred to as participants “You can observe a lot by just watching” Yogi Berra

3. 1.3 Types of Statistical Study Variables: Variable of interest- Items or quantities that the study seeks to measure Explanatory variable- Cause and effect Response variable- Variable which is a response to the cause and effect relationship

4. 1.3 Types of Statistical Study 3 Basic Types  Observational study – observe and measure statistics, do not influence or modify characteristics  Experiment – apply treatment then observe effects  Meta-analysis – study a topic that considers previous studies to find trends not evident in original study

5. 1.3 Types of Statistical Study Observational Studies: Retrospective study (Case-control) - Uses data from the past.  When do you think this type of study is most prevalent?  Ethics??? Prospective study (Longitudinal) - Set up to collect data in the future from a predetermined sample.

6. 1.3 Types of Statistical Study Case-control study (Retrospective) – observational study that resembles an experiment because the subjects naturally divide into groups.  Cases – engage in behavior  Control – do not engage in behavior  Used many times when an experiment may be deemed unethical, allow subjects to voluntarily exhibit behavior (i.e. Do seat belts save lives? Make sure you wear your seatbelt!)

7. 1.3 Types of Statistical Study Study Groups:  Treatment group – receive treatment  Control group- do not receive treatment Note: Study could involve more than two groups, and the groups should be chosen randomly from larger sample

8. 1.3 Types of Statistical Study Confounding – can not determine the effects of specific factors Confounding factors – factors that lead to confusion

9. 1.3 Types of Statistical Study Strategies For Selecting Groups  Use a randomized experiment – participants assigned randomly  Use a large number of participants – unlikely to differ in significant way

10. 1.3 Types of Statistical Study Placebo – Identical in appearance to the treatment, but lacks active ingredient, participants can not distinguish Placebo effect – patients improve simply because they believe receiving treatment (i.e. power of suggestion) Experimenter effect – when experimenter somehow influences subjects through factors such as facial expression, tone of voice, or attitude (i.e. education: self-fulfilling prophecy)

11. 1.3 Types of Statistical Study Single-blind – participant does not know which group they are part of Double-blind – participant nor experimenters know who belongs to which group

12. 1.3 Types of Statistical Study

13. Which type of Study? a. What is the mean income of stock brokers? Observational b. Can lifting weights improve runner’s times? Experiment, no blinding c. Does skin contact with particular glue cause rash? Experiment, single-blind, not double-blind because experimenter can not cause a rash d. Can a new herbal tea remedy reduce severity of cold? Double-blind experiment, severity of cold may be influenced by experimenter e. Dozens of individual studies have given contradictory results, can exercise increase life span? Meta-analysis

14. 1.3 Types of Statistical Study Summary  Why do we need a control group?  What two strategies do we keep in mind when choosing groups?  What is a placebo?  Actual example of experimenter effect?  When are case-control studies usually used? Class work—pg 32 #9-28 all