## 10.8Optional: $$P$$-values

(Answers available in Sect. A.10)

An ecologist is studying two different grasses to help combat soil salinity, by comparing to a new grass (Grass A) to a native grass (Grass B).

She uses 50 different sites, allocating the two grasses at random to the sites (25 sites for each grass).

After 12 months, the ecologist records whether the soil salinity at each site has improved, and hence computes the odds that each grass will improve the salinity.

She finds a statistically significant difference between the odds in the two groups.

Which of these statements is consistent with this conclusion?

1. The $$\text{OR}=4.1$$ and $$P=0.36$$
2. The $$\text{OR}=4.1$$ and $$P=0.0001$$
3. The $$\text{OR}=0.91$$ and $$P=0.36$$
4. The $$\text{OR}=0.91$$ and $$P=0.0001$$

How would the other statements be interpreted then?