Question

Ornithologists conduct three studies to understand why different individual birds lay different numbers of eggs. They wonder whether the species a bird belongs to might explain at least some of the differences. In each study, ornithologists count eggs in 20 nests of each of three different species. These data are summarized in the tables below.


Which study provides the strongest evidence that bird species contributes to the difference in the number of eggs per nest?

Study 1

species	mean	standard deviation
scrub jay	3.1	1.5
crow	5.2	1.5
magpie	7.1	1.5

Study 2

species	mean	standard deviation
junco	3.1	3.2
sparrow	5.2	3.2
mallard	7.1	3.2

Study 3

species	mean	standard deviation
yellowlegs	4.9	3.2
merganser	5.2	3.2
gull	5.1	3.2

Answer 1

Study 1 has the smallest standard deviation for all three species compared to the remaining three studies. Also, the magnitude of difference between the mean values for three species is large for Study 1 compares with Study 3 even if Study 1 has same magnitude for this difference with Study 2. Hence, base on the standard deviation and magnitude for this difference between the means within the studies we can say that Study 1 provides the strongest evidence that bird species contribute to the difference in the number of eggs per nest.