An inference question about a study tests which conclusion follows from the researchers’ comparisons. Read the lead-in to see whether you need a conclusion, prediction, or limit. When the study gives both overall averages and results within smaller groups, keep those comparisons separate and name what each shows. Then ask what changed between the groups and what stayed the same, so you can predict the smallest supported conclusion. An overall difference doesn’t always mean the same difference exists within every group.
Hints
- Hint 1
Separate the two comparisons: all city nests versus all rural nests, and city versus rural nests within each species. What does each comparison show?
- Hint 2
Read the warm-spring finding on its own. What does it test that the city-versus-countryside comparison doesn’t?
- Hint 3
Look for how the findings fit together. What can you conclude from the overall dates, the dates within each species, and the warm-spring results?
Step-by-step
Compare the overall average with each species
Step 1Separate the overall result
The average date across all city nests was earlier than the rural average, so we need to explain that gap using the whole analysis. Does it show the same birds nesting earlier, or different kinds of birds being counted? Because this average combines species, the overall gap doesn’t settle what happened within each species.
- Step 2
Find what differs between habitats
Within each of 18 species, the median nesting dates, or middle dates, differed by no more than one day across habitats. What could still make the overall averages differ? Cities had a much larger proportion of year-round resident species, which typically nest earlier than migratory species in both habitats. That larger share can pull the citywide average earlier without any species changing its own schedule much.
- Step 3
Account for the warm springs
What does the warm-spring result add? The text says unusually warm springs advanced nesting by similar amounts for city and rural populations of a given species. So temperature can move nesting dates earlier in both habitats. Birds can nest at nearly the same time in cities and the countryside and still both start earlier in a warm spring.
- Step 4
Keep the conclusion small
Which wording stays within those findings? The phrase mainly reflects which species are common explains the citywide average without claiming that this is the only possible cause. And not a substantial urban shift allows the small differences between habitats instead of claiming an exact match. Choice A.