Question 18M.3.SL.TZ2.b
| Date | May 2018 | Marks available | [Maximum mark: 3] | Reference code | 18M.3.SL.TZ2.b |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Outline | Question number | b | Adapted from | N/A |
White sage (Salvia apiana) is a native Californian shrub. Slender oat (Avena barbata) is a grass, originally from the Mediterranean, which was introduced to California. The map shows the distribution of the two species in relation to one another in an area near Santa Ynez, California.
Outline how chi-squared can be used to test for an association between the distributions of the two species.
[3]
a. in each quadrat determine the presence/absence «of plants» of each type
b. null hypothesis is that the presence of one is random/independent in relation to the presence of the other plant
OR
alternate hypothesis is that the presence of one is associated with the presence or absence of the other
c.
Equation may be written out in words.
d. accept alternative hypothesis / reject null hypothesis if the difference between observed and expected is statistically significant / p<0.05 /calculated X2 higher than tabulated X2 / critical value
OR
it supports the association between the two species if the difference between observed and expected is statistically significant / p<0.05 /calculated X2 higher than tabulated X2 / critical value
