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\bf{THE ROLE OF RANDOMIZATION IN ESTABLISHING CAUSATION}

R.W. Oldford\\
	Department of Statistics and Actuarial Science\\
        University of Waterloo
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{\em Key Words: Randomization, causation, confounding, lurking variables,
3-d geometry, physical demonstrations, student labs}

The role of randomization in experimental design is often poorly
understood by students of statistics.
Part of the reason for this lies with our traditional presentations.
Randomization is critically important to provide a simple compelling
argument for the existence of a causal relationship from factor to response.
In this talk, I describe and demonstrate a simple physical device that
makes this point.
The device can also be used to demonstrate how simple randomization tests work
but this is far less important.
The device can be used by a speaker on an overhead projector and/or directly
by students in a laboratory setup.
The device has been used in both fashions at Waterloo in a first course in
statistics.
Some of that experience will related.

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