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A Room can be affected by the overall stat level of all the Dwellers that are currently assigned to a room. For example, the Water Treatment rooms are affected by Perception.
Now the max stat that a Dweller can have naturally is 10. However, you can give a Dweller an outfit that might boost a certain Stat.
For example, the Armoured Vault Suit grants a +3 to Perception. If a Dweller has 10 Perception already, will this contribute toward the overall "Room Level"? Or would it be better suited giving this to a Dweller who's Perception is below 10?