# Threshold to consider the daily change of a bond price unusual?

In the context of compliance and market abuse monitoring, what relative change threshold would you choose to decide if transactions should be looked into?

For example, if a bond price had a relative price change of +/- X% and the bond was sold or bought around the time the price move occurred, there could be a market abuse (for example, insider knowledge).

I am trying to get a decent level in order to avoid false positives (the desk is mainly trading EM bonds).

How about using either option-implied or historically derived daily $$\sigma$$ and then setting a threshold of $$\pm 2\sigma$$ or what may seem reasonable to you?
I think you would also have to scan for a pattern. If the price jumped up by say $$+2\sigma$$ and then remained at that level, that would likely indicate some new information becoming generally available.
However, if there was a single trade up by $$+2\sigma$$ and the subsequent trades were again at the price level prevailing before the potentially suspicious trade, then that is clearly something you would want to look into further.