This AP story says:

Experts estimate that about 5% of all money donated by American Jews — and 20% donated particularly to Jewish causes — goes to Israel …

thus implying that only a quarter of American Jewish charity giving is donated specifically to Jewish causes. However, when you look at the report from which they are quoting and check the definitions, you find that:

Some grants to secular institutions were designated for Jewish purposes, for example, Jewish studies programs at universities. These are classified, nevertheless, as secular. Similarly, grants can be made to Jewish organizations to serve the general public, and these are classified as Jewish, because the grant recipient is a Jewish institution. All giving to Israel, regardless of purpose, is considered Jewish …
http://www.jewishresearch.org/PDFs/Jewish.Foundations.pdf (2007)

The artificially low figure of only 25% of all Jewish-American charity being donated to specifically ‘Jewish’ causes is obtained by not counting donations to non-religiously Jewish causes, such as, for example, Jewish studies programs at (secular) universities. Suppose that we added all the Jewish causes that are not religiously Jewish in the USA, we might reach 50%. Secular Jewish welfare organisations abound overwhelmingly, and none of them are included, from Jewish studies departments at (secular) universities, outwards.