| Date | May 2018 | Marks available | 1 | Reference code | 18M.3.SL.TZ2.2 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | Determine | Question number | 2 | Adapted from | N/A |
Question
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.
Using the scale bar, determine the area of quadrat A1, giving the units.
Outline how chi-squared can be used to test for an association between the distributions of the two species.
Markscheme
9.0 m2 / 9 m2
Units required for the mark.
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. \({x^2} = \sum {\frac{{{{\left( {O - E} \right)}^2}}}{E}} \)
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
