252rubric 10/4/06
Possible Rubric for Statistics Exams and Papers
I have been hearing a lot about rubrics lately, and have taken a while to be assured that they are not
the materials that the third pig built his house out of. My first attempt at this came to me in an assessment
meeting. It is slightly expanded here.
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Did the student make a good effort to understand the question? This would include asking
the instructor and consulting notes and texts if he/she did not understand what was
desired.
Was the method used to solve the problem the best and most appropriate for the problem?
Was the method used correctly?
Did the student present the solution in such a way that the instructor can understand how
the student got the answers presented? This should include all formulas, equations and
tables used. If there are parts to a problem, are they clearly labeled? Is it evident from the
way the work is presented that the student understood what he/she was doing? Is it
legible?
Was the conclusion stated clearly? Was the null hypotheses rejected or not rejected? Was
a valid null and alternate hypothesis clearly stated at the beginning? What were the
implications of the conclusion for a relevant goal, for example the decision to buy a new
product?
Did the student demonstrate knowledge of the difference between sample statistics and
population parameters? Was a statistical test using sample statistics used to evaluate a null
hypothesis containing population parameters and an equality?
In view of what was said here, it is incredible that, on every exam I give, students give me confidence
intervals and tests for means when I ask for confidence intervals and tests for medians, variances and even
proportions. Check the wording on the questions that you misunderstood. Can you identify what wording in
the question made you think it was about a mean? Can you tell me what it was? It is also remarkable that
there are any people out there who do not know that proportions, probabilities and p-values (which are
probabilities) must be between one and zero. It is also amazing to me that that so many of you cannot
express the difference between t and z . In the most practical sense a value of t  comes from the t table
and must be used with s , the sample standard deviation, in confidence intervals and in tests for the
population mean. There are a few other cases where we use t  and they will be discussed later in the
course. On the other hand z  , which comes only from the bottom line of the t table, but can be calculated
using the table of the standardized Normal distribution, must be used with  , the population standard
deviation, in confidence intervals and tests for the mean. z  is also used in large sample tests for the
population proportion, population mean, population standard deviation, population median and the means
of the Poisson and Binomial distribution if the correct formulas are used, but don’t push it. The Normal
distribution should not be used if more accurate methods are available. In any case, look at Things You
Should Never Do on and Exam or Anywhere Else before you do another assignment and frequently
thereafter.
Roger Even Bove
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