Question

1. migrating sandhill cranes sometimes suffer injuries or death from powerlines. to minimize these collisions, the acme power company started installing highly visible markers for any new powerline installed in the past two years. a recent investigation found that the number of injured and dead cranes found under the wires with markers is statistically significantly smaller than the number found under the wires without markers. which of the following can be concluded from this study?

a) the use of the highly visible markers decreases the risk of powerline collision.
b) there is an association between markers and the number of powerline collisions, but not necessarily a causal relationship.
c) there is an association between the presence of markers and the number of powerline collisions, but not a correlation.
d) there is no association between markers and the number of powerline collisions.
e) these conclusions can be extended to migrating whooping cranes.

Explanation:

In observational studies (like this one where markers were installed and the number of injured/dead cranes was observed), we can establish an association. However, without a controlled experiment (where all other variables are strictly controlled), we cannot be certain of a causal relationship. Just because there are fewer injured/dead cranes under wires with markers doesn't mean the markers are the sole cause (there could be other factors like the location of the new power - lines, etc.).

• Option A claims a causal relationship (decreases the risk) which is too strong for an observational study.
• Option C is incorrect because an association implies a correlation.
• Option D is wrong as the data shows a difference (so there is an association).
• Option E is incorrect as the study is about sandhill cranes and there is no basis to extend it to whooping cranes.

Answer:

B. There is an association between markers and the number of powerline collisions, but not necessarily a causal relationship.