From a July 30 New York Observer article:

To wit: According to The Observer's analysis of Nielsen data, in recent weeks, as criticism of Mr. Dobbs has continued to go up, his ratings at CNN have continued to go down.

Mr. Dobbs' first began reporting on Obama birth certificate conspiracy theories on the night of Wednesday, July 15. In the roughly two weeks since then, from July 15 through July 28, Mr. Dobbs' 7 p.m. show on CNN has averaged 653,000 total viewers and 157,000 in the 25-54 demo.

By contrast, during the first two weeks of the month (July 1 to July 14) Mr. Dobbs averaged 771,000 total viewers and 218,000 in the 25-54 demo. In other words, Mr. Dobbs' audience has decreased 15 percent in total viewers and 27 percent in the demo since the start of the controversy.

Arguably, interest in cable news has slumped across the board since early July when attention over Michael Jackson's death was still at a fever pitch.

But, that said, Mr. Dobbs' ratings over the past two weeks, during the height of the “birthers” controversy, are also down significantly compared to his overall numbers during the second quarter of 2009 when he averaged 769,000 total viewers and 222,000 in the 25-54 demo.

In summary, if Mr. Dobbs' affinity for “birthers” is a ratings ploy, it's a pretty ineffective one.

Previously:

Fox's Chris Wallace: Lou Dobbs looking like “grassy knoll nut,” wonders if CNN would advance flat earth theories

Goldberg on Dobbs' birther coverage: “If ratings would go up by doing this, [CNN Pres. Klein would] have no problem about the image”