single?

[Eway]

"Stop smoking. This is the single most important factor in preventing a further heart attack."

The article I'm reading also suggests other factors to prevent heart attacks. Why does it use "single" here?

[curmudgeon]

"Stop smoking. This is the single most important factor in preventing a further heart attack."

The article I'm reading also suggests other factors to prevent heart attacks. Why does it use "single" here?

I think the author is saying that, although there are other preventative measures that can be taken to reduce the risk of a heart attack, the most important one is to stop smoking.