The Traffic Accident Reconstruction Origin Article

Special Studentt Table *
It is recommended that the reader print this page to work the example problems.
Probability Percent 
t(50%) 
t(90%) 
t(95%) 
t(99%) 

Number of Tests n * 

5 
0.741 
2.13 
2.77 
4.61 

10 
0.703 
1.83 
2.26 
3.25 

15 
0.692 
1.76 
2.15 
2.98 

20 
0.688 
1.73 
2.10 
2.86 

30 
0.683 
1.70 
2.04 
2.75 

40 
0.681 
1.68 
2.02 
2.70 

50 
0.680 
1.68 
2.01 
2.68 

Infinite 
0.674 
1.65 
1.96 
2.57 
This table is used to find the testimator . For example the testimator for 5 tests (n=5) at 99% probability is 2.13. Similarly =2.70.
Several observations can be made from simply examining the table.
Recall that the testimator is a factor for that is used to multiply Standard deviation to determine uncertainty. It should then be apparent that choosing a smaller probability will result in a smaller value for uncertainty. For example the testimator for 20 samples at 50% probability is .688, while the 99% testimator for 20 samples is 2.86. Similarly, trials with more samples will also reduce the range of uncertainty. This is illustrated by the observation that is greater than (4.61>2.68).
The lesson offered by the table is that high probability estimates result from repetitive measurements.
* This table may be used accurately with the equations supplied within this article. The reader may note that this abbreviated Studentt table has values slightly different that other such tables. This difference arises from the simplifying step listing Number of Tests rather than (degrees of freedom) in the left column. Other tables typically list (= n1) in the left column. Cell values in this table have been adjusted to the index n rather than .
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