Is it OK to use this expression in an academic text?
The given charts represent ball-park figures of mortality rates in European countries.
Is ball-park formal enough to be used in an academic context?
Formal Language – Is Ball-Park Figure Formal or Informal?
formal-languageformality
Best Answer
There is no single authority to which one would turn to determine whether phrasing is "formal" enough for a situation; sometimes, even in an academic paper or a public address, colloquial phrasing is more communicative of tone, region, familiarity, and so forth. Whether it is acceptable is a judgment your audience makes.
Merriam-Webster does not mark the noun or adjective uses of ballpark to mean approximation or approximately correct as informal. It does mark the verb use, to make a rough estimate, as informal. So in Webster's eyes, the first two have become normalized for broad usage, but the latter has not.
The American Heritage Dictionary, which is historically a more conservative dictionary — it was created in part because Webster's Third International Dictionary was criticized as too permissive — marks the noun and adjective sense of ballpark meaning approximate not merely as informal, but as slang, suggesting it be avoided in serious writing.
For another consideration, the principal meaning of ballpark is a field used to play baseball, and as a metaphor it was first popularized in U.S. military slang. As you might expect, it is much more commonplace in American English compared to other varieties, borne out by the NGram. The OED marks the term as originally and chiefly U.S.
Given this, you might prefer ballpark as a more colorful term, or one familiar to U.S. audiences, but if you want to maintain a drier tone, synonyms like approximate, estimated, or on the order of might be suitable, with roughly, or simply around also possibilities.