Hello,
From the tutorial, the stats you mentioned are described as:
Atrophy is the rate at which all a crew's skills, except for Morale, will decline per league race. Training or increasing salary can counteract atrophy.
Variance is also affected by salary and determines the amount of variance in a pit crew's performance. Higher variance means they may less reliably deliver their peak performance.
Pit crew
morale behaves differently to driver morale and even skills of the other Pit Crew. In each league race, higher salaried crews gain morale, whereas lower paid crews lose it.
On a side note, all iGP Manager tutorials can be re-enabled by following this link -
https://igpmanager.com/app/p=help&tab=support