Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Significance of Findings
Name: Tierra H.
Status: student	
Age:  N/A
Location: N/A
Country: N/A
Date: 5/18/2004


Question:
If a finding is statistically significant, why is it also necessary to consider practical significance?



Replies:
One has to be aware that statistics is a discipline for handling our ignorance. If we know that A causes B, or A and B are correlated (that is, if A changes by so much, then B changes by some amount), we do not need statistics. The language of statistics, especially regarding cause and effect, is very precise, very careful, and a bit daunting.

For example: A fictional statistician might say something like, "If repeated measurement of some variable, X, is normally and randomly distributed about the mean, M, with standard deviation, S, then with a confidence level of 0.YZ (usually 0.95 or 0.99) we can say that any values of X that differ from the mean, M, may be explained by random fluctuations in the variable, X, and hence are not statistically significant.

Now there are a lot of "if" conditions in such a statement: Differences are normally and randomly distributed about M means there are no more than one "hump" in the measurements, that the difference between X and M MAY be due to random fluctuations alone, and some more hidden "ifs". There are also other types of distributions that do not have a "bell-shaped" curve like the above. What statistics does is provide us with a "warning" that something MAY be happening with the variable X that makes its value "significantly" different than M. It's not a certainty. If X differs from M more than what random fluctuations can "explain" then it says, "Hey, you better check this out!" You do not have to, it is just a consistent way of identifying when some X is significantly different than the average, M.

Vince Calder



Click here to return to the Mathematics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory