Fraction, by itself, is kind of meaningless. The idiom small fraction, when used in contexts similar to the above, would better fit your intent, I suspect.

Also, "Among the 20,000 members who were..."

Thanks both, "small fraction" seems a good option.

In this case, I might go with tiny fraction.

Thank you so much, is there any single word synonym for "tiny fraction"?

I was just looking for such a word but came up empty. I found a number of words that mean small number or quantity, but not small fraction. You might want to edit or rephrase your question a little bit (no pun intended) to focus more directly on your desire for a single word that means a small, very small, or tiny fraction.

You could use the word Fragment instead.

Thank you. tiny fraction fits my intent. I preferred to use a single word, but not necessarily. That's why I avoid using single-word as a tag.