10.1 Quick revision

We strongly recommend trying these Quick revision questions before your tutorial.

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?

The $\text{OR} = 4.1$ and $P = 0.36$ .
Consistent with conclusion NOT consistent with conclusion
The $\text{OR} = 4.1$ and $P = 0.0001$ .

Consistent with conclusion NOT consistent with conclusion
The $\text{OR} = 0.91$ and $P = 0.36$ .

Consistent with conclusion NOT consistent with conclusion
The $\text{OR} = 0.91$ and $P = 0.0001$ .

Consistent with conclusion NOT consistent with conclusion

How would the other statements be interpreted then?

0 of 4 correct

Statements 2 and 4 are **both* consistent with the information (small $P$ -value).