Centuries Used Adjectivally: Hyphenated?

[Allthatjazznj]

Which is the correct punctuation for centuries, when spelled out, used adjectivally--for example, "This is a twentiety-century phenomenon" or "This is a twentieth century phenomenon"?

I cannot find this answer in the Chicago Manual of Style.

Any help would be appreciated. :?

[Susie Smith]

Which is the correct punctuation for centuries, when spelled out, used adjectivally--for example, "This is a twentiety-century phenomenon" or "This is a twentieth century phenomenon"?

I cannot find this answer in the Chicago Manual of Style.

Any help would be appreciated. :?

This is a twentieth-century phenomenon.

Use a hyphen to connect two or more words functioning together as an adjective before a noun.
She is not yet a well-known candidate.

Generally, do not use a hyphen when such compounds follow the noun.
After our television campaign, she will be well known.

Source: A Writer's Reference by Diana Hacker

[Allthatjazznj]

Thanks. That would have been my judgment as well, though I find inconsistencies with the use of centuries. Also, what about percentages. "A 15-percent increase"? I often see "A 15 percent increase." Do percentages follow your same rule?

Use a hyphen to connect two or more words functioning together as an adjective before a noun.
She is not yet a well-known candidate.

Generally, do not use a hyphen when such compounds follow the noun.
After our television campaign, she will be well known.

[Susie Smith]

Thanks. That would have been my judgment as well, though I find inconsistencies with the use of centuries. Also, what about percentages. "A 15-percent increase"? I often see "A 15 percent increase." Do percentages follow your same rule?

Use a hyphen to connect two or more words functioning together as an adjective before a noun.
She is not yet a well-known candidate.

Generally, do not use a hyphen when such compounds follow the noun.
After our television campaign, she will be well known.

I'd say "a 15 percent increase".

[MikeNewYork]

Thanks. That would have been my judgment as well, though I find inconsistencies with the use of centuries. Also, what about percentages. "A 15-percent increase"? I often see "A 15 percent increase." Do percentages follow your same rule?

Use a hyphen to connect two or more words functioning together as an adjective before a noun.
She is not yet a well-known candidate.

Generally, do not use a hyphen when such compounds follow the noun.
After our television campaign, she will be well known.

Most style manuals I have seen do not recommend a hyphen in percents, even when they appear before a noun.