Ummmmmmmmmmmmmm .... to fool them too?
Security analyst reports are used to make decisions.
If you desire decisions to be made a certain way you would alter the reports appropriately.
So if you want ISIS to have time to take a certain city in Iraq you would write the report underestimating their strength and progress in that area.
Given that some of these reports are read by congress and their staff, If you want Iran to have more time to build their nuclear weapon you would suggest in your report that their centrifuges are not as efficient as you truly believe them to be.