* Definition of "away": Does this mean out of state, out of the county, or simply away from their family home? The definition greatly impacts the statistic.
* Country: The percentage will differ drastically between countries with varying higher education systems and demographics. The US, for example, will have a different rate than a country with a more centralized higher education system.
* Socioeconomic factors: Students from wealthier families are more likely to attend college farther from home.
* Type of college: Students attending community colleges are much more likely to remain near home than those attending four-year universities, particularly private ones.
To get a meaningful answer, you'd need to specify these factors. For instance, you might ask, "What percentage of US students attend a four-year college outside of their home state?" Even then, finding precise, up-to-the-minute data can be challenging. The National Center for Education Statistics (NCES) in the US, or equivalent organizations in other countries, would be the best source for such information.