Question 22M.2.HL.TZ2.c
| Date | May 2022 | Marks available | [Maximum mark: 1] | Reference code | 22M.2.HL.TZ2.c |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | State | Question number | c | Adapted from | N/A |
A group of students used quadrat sampling and the chi-squared test to find out whether the distributions of two plant species were associated with each other or not. These two species were found in the ground vegetation in a woodland ecosystem.
[Source: (left) Pixabay.
(right) Topic, J., n.d. Veronica montana 2. [image online] Available at: http://www.freenatureimages.eu/Plants/
Flora%20S-Z/Veronica%20montana/#Veronica%2520montana%25202%252C%2520Bosereprijs%252C%2520Saxifr
aga-Jasenka%2520Topic.jpg [Accessed 3 December 2019].
The numbers of quadrats with one, both or neither species present were counted and recorded. The observed frequencies from 150 quadrats are shown in the following contingency table.
State the number of degrees of freedom for this test to determine the critical value of chi-squared.
[1]
1 (df)
OR
(r-1) (c-1);
Calculating the degrees of freedom proved problematic for many.
