In its recent Banking Analytics Blog FICO explains why there were significant swings in credit scores.

In the worst part of the recession from 2008 to 2009, the FICO® 8 Scores for approximately 50 million people declined by more than 20 points. Two-fifths of this group (nearly 21 million) saw their scores decline by more than 50 points. Clearly many of those shifts reflected increased risk brought about by credit delinquencies, loan defaults and other indicators of financial trouble.

The picture then began to improve. By 2010-2011, approximately 40 million consumers experienced a score drop of more than 20 points, 20 percent fewer than in 2008-2009. Similarly, the scores for roughly 15 million people dropped by more than 50 points in 2010-2011, 28 percent fewer than in 2008-2009.

While this was going on, the FICO® 8 Scores of many other people were moving upward. During 2010-2011, the scores of approximately 49 million people increased by more than 20 points. Even at the peak of the recession in 2008-2009, nearly 44 million people experienced a score increase greater than 20 points. Actions by both consumers and lenders likely contributed to this score improvement. In part, it is a natural consequence of people treating credit more carefully in a time of uncertainty by paying down their card balances, postponing new loans, and continuing to pay bills on time.

Setting aside the recession’s impact, a healthy chunk of the population remains very true to their credit behavior. During 2008-2011, nearly a third of consumers (approximately 65 million) maintained a FICO® Score within 10 points from year to year. Particularly consistent in their habits are those consumers with very high (800-850) and very low (300-499) scores on the FICO Score range of 300-850. Approximately 6 out of 10 consumers with a score under 500 in 2010 remained in this group 12 months later. For the very high scoring population, nearly 8 out of 10 consumers with a score of 800 or better in 2010 still had a score of 800 or better in 2011.

Source: FICO Banking Analytics Blog