From PeHub:

[Angelsoft] reported that valuations for funded startups in Q4 of 2008 fell by 24% when compared to Q3 of the same year

This data is based on a relatively small sample size (c120 companies) and is drawn from Angelsoft’s software which is used by angels and some (mainly smaller) VCs – so whilst I think this datapoint is directionally correct I’m treating the it with some caution.