The phrase "are difficult to compile" is correct and usable in written English.
It can be used when discussing information, data, or resources that are challenging to gather or organize.
Example: "The statistics from various sources are difficult to compile, leading to inconsistencies in the report."
Alternatives: "are hard to gather" or "are challenging to assemble."
Even when such cases reach court, they are difficult to compile because there is often no clear physical evidence linking a stalker to the victim.
Exact statistics are difficult to compile, in part because IDPs may be cut off from international access and assistance or compelled to go into hiding because of threats to their life or safety.
Precise numbers to back that up are difficult to compile, though Shapiro noted that while animal rights groups only conduct an estimated five to 10 investigations each year, abuse is discovered with "troubling frequency".
Furthermore, comprehensive expression profiles are difficult to compile for all cellular conditions.
However, such estimates are difficult to compile and comparison between countries needs careful calibration [ 1].
However, such estimates are difficult to compile and comparison between countries needs careful calibration.
The 115 million figure was difficult to compile because recording criteria differed greatly from country to country.
Estimates of the number of Iraqi military and civilian casualties in the war have been difficult to compile, and vary widely.
While exact data on monitor timeouts is difficult to compile, several coaches and players said that it felt as if officials were using replay more often this season.
An accurate count of the casualties was difficult to compile because more than half the stricken villages had not yet been reached by rescue teams.
Since residents typically bury their dead quickly, in line with Afghan custom and Islamic practice, precise details on the deaths have been difficult to compile.
