T-test paired

Paired t-tests Changes in constitutive calcitonin receptor responses with 100 nM AC512. 

As can be seen from the analysis in Table 11.3, the paired t-test indicates that the effect of AC512 on the constitutive activity is significant at the 99% level of confidence (p<0.01 and AC512 is an inverse agonist and does decrease the constitutive receptor activity of calcitonin receptors). 

Example 7. The -test using samples of differing composition (the paired t-test). 

If you do not have the change-from-baseline variable, ldl change, calculated but you have the baseline variable, ldl base, and post-treatment variable, ldl post trt, then you can run this comparison as a paired t-test, like this ... 

The data were statistically analyzed using the SOLO Statistical System (BMDP Statistical Software, Inc., Los Angeles, CA) on a personal computer. Differences between groups were tested by the Mann-Whitney test or a paired t-test in cases where paired data sets were tested. Possible relationships were studied with (multiple) linear regression using least-square estimates. 

The wheat bran used in these studies was milled for us from a single lot of Waldron hard red spring wheat. Other foods and diet ingredients were purchased from local food suppliers. Data from HS-I was analyzed statistically by Student s paired t test, each subject acting as his own control. A three-way analysis of variance (ANOVA) was performed to test for significant differences betwen diet treatments, periods and individuals in HS-II and HS-III. 

The two-sample t-test is only applicable, if the data are collected from analysing the same sample several times. If the data come from the analysis of different samples where the differences between the samples are much greater than the differences between the two methods or the two laboratories, it is necessary to apply the paired t-test. 

The data are used to perform a paired t-test (see Basic Statistics ). 

FIGURE 5.10 Intracellular CoQio content in BMC pre- and postsupplementation (14 days). Values are expressed as mean SD. Volunteers with baseline levels <12 pmol/pg DNA were pooled (n = 41) p < 0.05 paired t-test. 

The paired t-test also known as the one-sample t-test was also developed by Cosset. This test is primarily used for the analysis of data arising from within-patient designs, although we also see it applied when comparing a baseline value with a final value within the same treatment group. 

The final column above has calculated the A — B differences and as we shall see, the paired t-test works entirely on the column of differences. Again we will follow through several steps for the calculation of the p-value for the A versus B comparison ... 

Paired t-test of baseline with week 8 in the active A group, p 0.001 (this means the p-value is very much less than 0.001)... 

Comments as above for the between-patient designs apply also for the within-patient designs and in many cases the best approach will be to focus on a sequence of pairwise comparisons using the paired t-test. 

For the paired t-test, the standard deviation of the within-patient differences for the primary endpoint needs to be specified and again, the level of effect to be detected. 

In the paired t-test setting it is the normality of the differences (response on A — response on B) that is required for the validity of the test. The log transformation on the original data can sometimes be effective in this case in recovering normality for these differences. In other settings, such as ANOVA, ANCOVA and regression, log transforming the outcome variable is always worth trying, where this is a strictly positive quantity, as an initial attempt to recover normality. 

This test is the non-parametric equivalent of the paired t-test. Recall from Section 11.3 that the paired t-test assumes that the population of differences for each patient follows the normal shape. If this assumption is violated then the paired t-test does not apply although, as with the unpaired t-test, the paired t-test is fairly robust against modest departures from normality. 

By June 11 all of the field load Insects had died or left the trees. Leaf damage to the test trees when measured on June 3 was relatively light. Leaves exhibiting noticeable damage averaged 27.6 i 2.1% (S.E.) for the control trees and 49.0 i 4.7% for test trees (p < 0.01, one-tailed paired t test). Estimated leaf area loss averaged 2.5 + 0.2% for controls and 11.3 i 2.1% for test trees (p < 0.005, one-tailed paired t test). Damage to control trees was due to unidentified insects other than tent caterpillars. 

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