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Philosophy of Science & Experimental Design

Lecture Notes


Experimental design “A planned interference in the natural order of events.”
Subject(s) Means the subject under study, which can be people, technology and natural phenomena.
Sample Typically you can't study all the individuals of a particular subject pool, so in your experiment you use a sample and hope that the results generalize to the rest of the subjects.
Between subjects vs. within subjects design Between subjects: Two separate groups of subject/phenomena measured.
Within subjects: Same subjects/phenomena measured twice, on different occasions
Quasi-Experimental When conditions do not permit an ideal design to be used and a controlled experiement is impossible, there are other techniques that can be used. These are called quasi-experimental designs.
Internal validity How likely is it that the independent variables caused the dependent variables?
External validity How likely is it that the results generalize to other instances of the phenomenon under study?

Correlational Studies & Quasi-Experimental Design

Correlation Some factors/variables co-vary when changes in one variable are related with changes in the other, negative or positive.
Correlation: Powerful tool Any variables in the world can be measured for correlation. Only two variables are needed (independent and dependent) for doing correlation studies.
Main operating principle behind correlation There is no causation without correlation.
Correlation: Pitfall Correlation does not imply causation
between the variables measured!
Quasi-experimental designs Purpose: Where true experimental design is not possible, approximate it.
If direct control over dependent/independent variables is not possible.
How it works 1. One-shot case study (no control group).
2. Single group pre- and post-test (minimal control)
3. ABAB: Single-group repeated measures (slightly less minimal control).
Limitations Much greater uncertainty as to the internal and external validity of the quasi-experiments than true experimental designs.


What is it? A more loose, pre-study using the intended experimental design to tune it.
A pre-study intended to gauge the nature, scales or other factors of the variables to be measured, or the subject to be measured.
Why and when Pilots are much more useful than you might think. Yes, it will increase the duration and effort of your experiment BUT: It can significantly improve the quality of the subsequent experiment in many cases. It will certainly clarify and sharpen the experimenter's understanding of one or more of: the experiment, experimental procedure, variables and subjects.
Bottom line Do not try to “save time” by skipping a pilot if a pilot study seems to makes sense.


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