<Tr> <Th> 30 </Th> <Td> 0.683 </Td> <Td> 0.854 </Td> <Td> 1.055 </Td> <Td> 1.310 </Td> <Td> 1.697 </Td> <Td> 2.042 </Td> <Td> 2.457 </Td> <Td> 2.750 </Td> <Td> 3.030 </Td> <Td> 3.385 </Td> <Td> 3.646 </Td> </Tr> <Tr> <Th> 40 </Th> <Td> 0.681 </Td> <Td> 0.851 </Td> <Td> 1.050 </Td> <Td> 1.303 </Td> <Td> 1.684 </Td> <Td> 2.021 </Td> <Td> 2.423 </Td> <Td> 2.704 </Td> <Td> 2.971 </Td> <Td> 3.307 </Td> <Td> 3.551 </Td> </Tr> <Tr> <Th> 50 </Th> <Td> 0.679 </Td> <Td> 0.849 </Td> <Td> 1.047 </Td> <Td> 1.299 </Td> <Td> 1.676 </Td> <Td> 2.009 </Td> <Td> 2.403 </Td> <Td> 2.678 </Td> <Td> 2.937 </Td> <Td> 3.261 </Td> <Td> 3.496 </Td> </Tr> <Tr> <Th> 60 </Th> <Td> 0.679 </Td> <Td> 0.848 </Td> <Td> 1.045 </Td> <Td> 1.296 </Td> <Td> 1.671 </Td> <Td> 2.000 </Td> <Td> 2.390 </Td> <Td> 2.660 </Td> <Td> 2.915 </Td> <Td> 3.232 </Td> <Td> 3.460 </Td> </Tr>

Which of the following is not the purpose of student's t-distributions