I am having trouble figuring out what the monthlyReturn command is doing.

That is, consider SPY

getSymbols("SPY")

I then do monthlyReturn(SPY)

2011-10-31     0.109147150
2011-11-30    -0.004063745
2011-12-30     0.004080326
2012-01-19     0.047490040

hmmm. November is negative.....
On Nov 1, Spy closed at 121.23 (adjusted close)
On Nov 30, Spy closed at 124.20 (adjusted close)

This gives a return for November of (124.2/121.23)-1 = 2.45%

For October
Oct 3, SPY = 109.24
OCT 31, SPY = 124.71

This gives a return for October of (124.71/109.24)-1 = 14.17%

Can anyone please explain the discrepancy? Am I defining monthly returns
incorrectly?

Thanks!

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