statistical reasoning intro to probability and statistics mr. spering – room 113

Statistical Reasoning

Intro to Probability and Statistics

Mr. Spering – Room 113

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


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


3 Basic TypesObservational 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


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.


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!)


Study Groups:Treatment group – receive treatmentControl group- do not receive treatment

Note: Study could involve more than two groups, and the groups should be chosen randomly from larger sample


Confounding – can not determine the effects of specific factors

Confounding factors – factors that lead to confusion


Strategies For Selecting GroupsUse a randomized experiment – participants

assigned randomlyUse a large number of participants – unlikely

to differ in significant way

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)


Single-blind – participant does not know which group they are part of

Double-blind – participant nor experimenters know who belongs to which group


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


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

statistical reasoning intro to probability and statistics mr. spering – room 113

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