Comparatively is similar to relatively. When using relatively it is common that you are comparing against general knowledge or an aforementioned entity(ies). When using comparatively, do you need to include the things getting "compared"?
The use of relatively and comparatively is the same; in both cases, the two 'entities' must either be stated or be obviously inferrable for the sentence to make sense. Note the definition of relatively and comparatively:
In a relative manner; in comparison with something else (TFD)
Relating to, based on, or involving comparison; in a relative manner; by comparison to something else. (TFD)
In the following, it's implied that the Democratic presidential field is perceived (by the Democrats) to be stronger than that of the Republicans:
Most Democratic strategists believe the Republican presidential field is comparatively weak. - NYT
Here, both entities are identified.
While growth is relatively weak today, prices in financial markets — even if not the housing market — have already rebounded from their levels at the nadir of the financial crisis. - NYT
This sentence makes no sense without knowing what bowling is being compared to. It's not general knowledge, and must be explained by a preceding sentence.
It might be argued that the award comes in a period when bowling is comparatively weak. - NYT
Likewise, this sentence would make no sense without knowing what Ohio is being compared to (implied: other states). It must be inferred:
The A.F.L.-C.I.O. is relatively weak in Ohio, and some tensions exist between public and private sector unions. - NYT
Here, relatively is self-referential:
Powerful turbines are able to capture power even when the wind is relatively weak... NYT