From a post-Oscar story in The Daily News: Anne Hathaway released a statement saying that she simply couldn’t stand to look like any other girl on the red carpet. . . . “And so I decided it was best for all involved to change my plans.” 

Shouldn’t there be another that in there? Or is there one too many? It’s the kind of question that often comes up in work by  international students. No, this is not a rerun of That? Which? WHAT???  (Oct. 3, 2012). In that post, that was a relative pronoun; here it’s a conjunction joining two clauses. Consider these sentences:

I suggest that Japanese students can polish their English by using “News de Eigo.”

The agency has also reminded airlines that they cannot exclude items like computers.

They found that women who achieved success were at times likely to oppose the rise of other women.

Notice that what follows that is a clause, expressing a complete thought, with subject, verb and object.

Sometimes, especially in speech, that is omitted because it’s understood:

They told us (that) it was time to vacate the room.

She told me that she was applying for an internship.

The deciding factor should be clarity. For example, from a recent student blog post:

On Tuesday S&P Dow Jones Indices released its Case-Shiller 20-city index, which showed the value of residential real estate rose 6.8 percent in 2012.

In this case, I’d insert that: . . . which showed that the value . . . Otherwise, it’s a little too easy for a reader who may not have had her second cup of coffee yet to read it as showed the value.

Let’s take another look at this sentence: They found that women who achieved success were at times likely to oppose the rise of other women. They found women? They found women who achieved success? No, they found that those women did something. If you read the sentence aloud, you might notice your voice dropping on that. It’s not so much a content word as a signal, a transition between one thought (they found something) and another (what they found). Some copy editors, especially those on pare-it-to-the-bone publications, would disagree, but I vote for clarity every time, even if that means an extra word or two.

To test whether your sentence needs that, read it aloud. If you stumble, chances are you need that; if it’s smooth and clear, you can probably do without.

So: Anne Hathaway released a statement saying that she simply couldn’t stand to look like any other girl on the red carpet. . . . “And so I decided (that) it was best for all involved to change my plans.” In this case, it wouldn’t be wrong to say that in both places. But it’s not necessary in either.