The most common and most likely answer to this crossword clue is the 10 letter word PSEPHOLOGY
I've seen this crossword clue in The Daily Telegraph
P
S
E
P
H
O
L
O
G
Y
Buddy explains!

The straight part
We know that "Making cross a subject in this study?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case making cross a subject in this study? = psephology.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PSEPHOLOGY mean?
PSEPHOLOGY noun- The predictive or statistical study of elections.
- An ancient Greek method of numerology, similar to gematria.