13. The results in this section are based on daily data due to the fairly short time period of relevance. The relative spread volatilities reported here thus seem to be much higher than those reported earlier for credit markets. Assuming that all daily spread changes are independent, and that a month contains about 20 business days, a 6% daily volatility would correspond to a monthly relative spread change volatility that is greater by a factor of , or more than 26%. This apparent discrepancy reflects in part the fact that the analysis in this section directly examines the spread volatilities of individual issuers, without any attempt to separate systematic from issuer-specific effects. If we compute the total spread volatility for an issuer using our estimates of systematic and idiosyncratic spread volatility updated through the 2007–2008 credit crisis (15% per month), the implied total spread volatility of about 21% per month is not so different from the daily results (converted to a monthly frequency) shown here for euro sovereigns. It also underscores the approximate nature of this square root rule and the difficulty of comparing daily and monthly volatilities.