Doing little to polish a reputation and image that has taken a public-relations drubbing this year, CNBC’s documentary “The Oprah Effect” plays like an infomercial for the marketing power of Oprah Winfrey, only conspicuously without the participation of the daytime diva herself.

The result is an hour produced by Bill Kurtis distinguished by its stunning ability to state the obvious — namely, that getting mentioned on Winfrey’s program helps move products — without any serious insight into why that’s the case, other than that Oprah is a trusted brand. Well, duh.

The special includes tips on how to get on Winfrey’s show (good luck with that) and success stories of those who have been featured. As for any of the darker aspects of “The Oprah Effect” — say, whether people spend money they don’t have on the host’s “favorite things,” or the vague cult-like qualities of Oprah worship — that will clearly have to wait for another hour.

Similarly, there’s zero mention of how Winfrey’s support apparatus and vetting process has experienced several much-publicized glitches in recent years, such as touting James Frey’s fabricated memoir or Herman Rosenblat’s bogus story about meeting his future wife at a Nazi concentration camp. Even ABC News was inspired to ask “Is Oprah’s Golden Touch Tarnished?” last December after the latest discredited yarn that was stamped with the Oprah seal of approval.

Not that you’d know about any of this from watching this cheerleading documentary, or learn about Winfrey’s occasional passion for potentially dubious products, persons and self-help regimens, from psychics to the Acai Berry diet.

Hosted by CNBC’s Carl Quintanilla, the special premieres May 28. But for all it’s worth, anybody truly interested in gaining a better grasp of “The Oprah Effect” would be better off simply taping “Oprah” and time-shifting it into primetime.