When you are citing a statistic or another specific fact, a signal phrase is often not necessary. In most cases, readers will understand that the citation refers to the statistic or fact (not the whole paragraph).

Of 295 white troops garrisoned at Fort Pillow, 168 were taken prisoner. Black troops fared worse, with only 58 of 262 captured and most of the rest presumably killed or wounded.¹²

There is nothing wrong, however, with using a signal phrase.

Shelby Foote notes that of 295 white troops garrisoned at Fort Pillow, 168 were taken prisoner but that black troops fared worse, with only 58 of 262 captured and most of the rest presumably killed or wounded.¹²