Post on 01-Jan-2016
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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
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
1.3 Types of Statistical Study
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
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.
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!)
1.3 Types of Statistical Study
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
1.3 Types of Statistical Study
Confounding – can not determine the effects of specific factors
Confounding factors – factors that lead to confusion
1.3 Types of Statistical Study
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)
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
1.3 Types of Statistical Study
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