The survey showed that in 2005, 29% of White students and 6% of Black students were considered at or above proficient in math, and by 2013, 33% of White students and 7% of Black students were at or above proficient. The analysis reports that the difference between scores from 2005 and 2013 was "statistically significant" for the White students but not for the Black students. Explain what statistical significance means in this context.