when we do a 2 sample t test ... where we are estimating the population
variances ... in the context of comparing means ... the test statistic ...
diff in means / standard error of differences ... is not exactly like a t
distribution with n1-1 + n2-1 degrees of freedom (without using the term
non central t)
would it be fair to tell students, as a thumb rule ... that in the case where:
ns are quite different ... AND, smaller variance associated with larger
n, and reverse ... is the situation where the test statistic above is when
we are LEAST comfortable saying that it follows (close to) a t
distribution with n1-1 + n2-1 degrees of freedom?
that is ... i want to set up the "red flag" condition for them ...
what are guidelines (if any) any of you have used in this situation?
_________________________________________________________
dennis roberts, educational psychology, penn state university
208 cedar, AC 8148632401, mailto:[EMAIL PROTECTED]
http://roberts.ed.psu.edu/users/droberts/drober~1.htm
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