Student’s t-factor

Table 1.3. Critical Student s t-Factors for the One- and Two-Sided Cases for Three Values of the Error Probability p and 7 Degrees of Freedom f...

Figure 4.47. Drug assay using HPLC respectively UV Spectroscopy. Correlation of HPLC and UV results obtained on four batches of a cream. The vertical error bars each give the mean + standard deviation of 6 HPLC determinations because the Student s t-factor for five d.f. is nearly equal to /6 (see Section 1.3.2), the bars can also be interpreted as 95% confidence limits. The circles connected by a line indicate the corresponding duplicate UV determinations. The proportionality line passes through the origin and the center of mass for the four coordinates. The drug is slightly overdosed (= 103-104% the traditional UV assay apparently is not as selective as it should be an interference adds about 4% to the result.

Using the correlation coefficients, calculate the Student s t factors, and display these (the larger this value, the more probable the correlation values below about 2 are insignificant). 

Using the Student s t factors and the number of degrees of freedom, calculate the probabilities p that correlations are due to chance alone (error probabilities) these are interpreted as follows ... 

Here, the uncertainty intervals are standard deviations multiplied by Student s t factor for 95% probability and 5 degrees of freedom (t = 2.571) [48]. 

Based on these estimates and literature values for the fugacity, Oldani and Bor obtained equation 14.31, from which they derived the reaction enthalpy and entropy at the mean temperature of the experimental temperature range (T = 272 K) Ar//2°72 = 58.6 2.6 kJ mol-1 and ATS 72 = 304 10 J K-1 mol-1. The uncertainty intervals are standard deviations multiplied by Student s t factor for 95% probability and 18 degrees of freedom (t = 2.101) [48]. 

QREDJrBL.dat Table 1.7 Reduced critical -values (division of -values for p = 0.05 by the appropriate Student s t-factor and SQR(2)), as used with the multiple range test in MULTI. 

Number of Degrees of Freedom V Maximum Value of Student s t Factor for the Significance Levels Indicated ... 

The reliability of the result is determined in ISO 1973 by calculating the 95% confidence interval of the mean and expressing this as a percentage of the mean value. If this is greater than 2%, the number of bundles tested is increased. The confidence interval is calculated using Student s t factor taken from statistical tables, but of course it is much easier if one simply uses the tables and equation in ISO 2602. 

The true analysis value is therefore enclosed by the confidence range VB (x) with a confidence level given by Student s t-factor. 

Here, MU is the measurement imcertainty at and t is Student s t-factor, which depends on the number of calibration points. 

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