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Paired t Test

Paired t Test. t value is calculated in a slightly different form difference between each of the paired measurements on each sample is computed. Average difference D is calculated and individual deviations of each from D are used to compute a standard deviation, s d

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Paired t Test

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  1. Paired t Test t value is calculated in a slightly different form difference between each of the paired measurements on each sample is computed

  2. Average difference D is calculated and individual deviations of each from D are used to compute a standard deviation, sd • t value is calculated from :

  3. Example You are developing a new analytical method for the determination of blood urea nitrogen (BUN). You want to determine whether you method differs significantly from a standard one for analyzing a range of sample concentrations expected to be found in the routine laboratory. It has been ascertained that the two methods have comparable precisions. Following are two sets of results for a number of individual samples.

  4. Solution :

  5. 95% confidence level is considered significant • 99% level is highly significant • Smaller the calculated t value, more confident that there is no significant difference between the two method

  6. Too low confidence level (e.g. 80%), likely to conclude erroneously that there is a significant difference between two methods (type I error) • On the other hand, too high confidence level will require too large a difference to detect (type II error) • If a calculated t value is near tabular value at the 95% confidence level, more tests should be run to ascertain definitely whether the two methods are significantly different

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