MedCalc 22 can read all previous file formats but when saved, the new file format is used. Important: files saved in MedCalc version 22 cannot be read by previous MedCalc versions. (Version 22.Version 22 introduces a new file format. Kirkwood BR, Sterne JAC (2003) Essential medical statistics, 2 nd ed.Altman DG (1991) Practical statistics for medical research. ![]() Note that in MedCalc P-values are always two-sided (or two-tailed). When the P-value is less than 0.05 (P<0.05), the conclusion is that the two means are significantly different. The P-value is the area of the t distribution with n 1 + n 2 − 2 degrees of freedom, that falls outside ± t (see Values of the t distribution table). The significance level, or P-value, is calculated using the t-test, with the value t calculated as: The standard error se of the difference between the two means is calculated as: Where s 1 and s 2 are the standard deviations of the two samples with sample sizes n 1 and n 2. The program first calculates the pooled standard deviation s:
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