In the Case II situation, the df for t equals the df for S x which is N-1. And Student s t is a family of distributions differing in their kurtosis . Like the z test, the critical values are obtained from a table. To determine the critical value of t from the table, you will need to know a , the df, and whether you are using a one or two-tailed test. The average IQ for the school as a whole is 102 with the standard deviation unavailable.
Bad kids have normal IQs.
102 Bad kids do not have normal IQs. Assumptions Sample is randomly selected. Population of IQ is normal. Reason is so that the sampling distribution of the mean will be normal. Although a large sample size would also produce a normally shaped sampling distribution, we will rarely use large samples.