Slots in Vegas looser during the week?

[AndysDaddy]

In another thread, fishyak made this observation:

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Trish & I have noticed that slots payout is a lot looser M-Th. than Fri-Sun. Call it soak the tourist or attract the local yokel mid-week, the result is the same. My wife doesn't win as much during the weekend trips and you don't see others winning at slots as well. Any confirmations or denials?

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Is this true? I'm sure its possible, but is it practical? How easy/hard/labor intensive is it to alter the payout rate for one machine, or a group of machines, or all machines?

Just wondering...