The phrase "narrower categories" is correct and usable in written English.
It refers to subgroups or more specific classifications within a broader category. Example: In this research, we will group the data into five broader categories and then analyze the findings within each of these categories by breaking them down into narrower categories such as age, gender, and education level.
Human rights belong to all humans on account of their humanity rather than membership of narrower categories such as citizenship, ethnicity or class.
They are given to people on account of their humanity rather than membership of narrower categories such as state or nation.
In the same way that television networks and general magazines have given way to cable channels and special-interest magazines, and even radio stations have shifted their programming to serve narrower and narrower categories, cars aimed at small segments of the market have eaten away at the midsize sedans that once filled the highways.
Sections of data were coded according to the main themes which were subsequently refined into narrower categories (Table 2).
Ethnicity was self-reported in narrower categories than most studies but still did not include specific nationality of origin.
By progressively restricting the analyses to narrower categories of sites, we further seek to characterize sites with predictable mutational effects, that is, unconditionally deleterious, neutral or beneficial.
And what about the somewhat narrower category of "video film history" (376 entries)?
Mr. Ricketts started the American Film Company to make movies from the rather narrower category of stories from American history.
According to KPMG the narrower category of farmland and agribusiness deals account for less than 1% of total Chinese investment in Australia in 2014, being worth $140m.
Esterases include lipases, which break ester bonds (between a carboxylic acid and an alcohol) in lipids, and phosphatases, which act analogously upon phosphates; a narrower category comprises the nucleases, which are phosphatases that hydrolyze nucleic acids.
In contexts where he can only be taken to be interested in the narrower category of fine art, Hume variously mentions painting, statuary, architecture, dance, poetry, and music.
