N​‌‍‍‍‌‍‍‍‌‍‍‍‌‌‌‌‌‌‍‍​o plagiarism How does the teeth statistic differ from the z statistic? 

What degree of freedoms? 

Why were there not necessary when d​‌‍‍‍‌‍‍‍‌‍‍‍‌‌‌‌‌‌‍‍​iscussed z scores?

 And why does one use in-1 rather than just in when calculating the standard deviation as estimated from a sample​‌‍‍‍‌‍‍‍‌‍‍‍‌‌‌‌‌‌‍‍​?