significant(ly)?

Not necessarily. That is why the word "significantly" was used.

Good answer. But if I had to put a figure on it, talking about stocks, I'd say more than 10%.

Early on when my wife and I were dating, as a joke we defined a significant change as 3%. Anything less than that wasn't worth mentioning. In your case, it depends on how much something regularly changes. In this case, if stocks routinely move up and down 5%, then 5% is not significant. 10% is probably a good number in this case. If you are talking about the birth rate in a country where the number is usually pretty stable, then a 3% move would be very significant.