How often do they normally occur during a year?
There is not really a 'schedule' to corrections. Right now, we would view this as more sector-rotation than a correction, as some sectors are seeing money flows. Year-end can be an unusual time for trading, and this year this combines with renewed AI fears to see a lot of stocks taking big hits. But we were close to new all time highs less than two weeks ago, and some consolidation was due. Investors seem very fearful despite forecasted earnings growth, which leads us to believe this decline will not turn into something worse. But, no one can really predict these things. Psychology can take markets further than fundamentals, but only in the short term. We have not yet seen a big spike in the volatility index (VIX) that usually accompanies major corrections.