cut off

[annajowers]

After looking through the examples, I am still confused how you find the cut-off value if sigma is unknown?

[Taeho Kim]

It depends on two information: i) confidence level and ii) degrees of freedom.

i) confidence level can be found in the problem statement and it will be in the bottom margin of the t-table.

ii) degrees of freedom is n-1 for single population mean and n1+n2-2 for comparing two means where n is the sample size, n1 and n2 are the sample sizes of sample 1 and sample 2. This can be found in the left margin of the t-table.

By crossing those to value, the cut-off can be obtained.