Paired samples t - test using R

Data

weight1 = c(89.8, 107.5, 105.7, 81.2, 99.3, 76.7, 100.7, 75.7, 90.3, 105.7, 81.2, 71.7, 71.2, 98, 116.6, 68.5)
weight2 = c(87.1, 102.1, 102.5, 78, 97.1, 73, 95.3, 73, 87.5, 102.5, 78.5, 69.9, 64.9, 93.4, 112.9, 63.5)

1. Normality test of the differences

diff = weight1 - weight2
shapiro.test(diff)

2. Paired samples t - test

t.test(weight1, weight2, paired = TRUE)

3. Wilcoxon Signed Rank Test. Non parametric option for paired samples

wilcox.test(weight1, weight2, paired = TRUE)

The above example is contained in the paragraph 3.6 of the book "Στατιστική ανάλυση με τη γλώσσα R" (in Greek, ISBN: 978-960-93-9445-1) published in Thessaloniki, 2017.