Nested IF Functions for Ranges

[vaccines]

Hi - I am trying to forecast percentages for the years 2010-2050 based on 2000-2009 historical data. I would like to forecast years 2010-2050 based on the following rules:

• If the % in years 2000-2009 (i.e. 2000, 2001, 2002..etc) are increasing steadily, continue up to 90%.
• If the % in years 2000-2009 are decreasing, flat, or up and down, increase 1% per year to 90%.

If the % difference between the 2000-2009 numbers are all positive, then I think I am apply the 1st rule and if there are any of the % differences are negative, I think I can apply the second rule. I tried the formula below but it's not working.
Columns C-M in the function below = 2000-2009 data

=IF((C17:M17<0),M17*1.01,MAX(0.9))

I also tried the following:
(C14>D14>E14>F14>G14>H14>I14>J14>K14>L14>M14,MAX(0.9),IF(C14<D14<E14<F14<G14<H14<I14<J14<K14<L14<M14,OR(C14=D14=E14=F14=G14=H14=I14=J14=K14=L14=M14),OR(C14<D14<E14<F14<G14<H14<I14<J14<L14<M14, font MAX(0.9)))< M14*1.01,>

I know there is something missing in these formulas, but am having a hard time figuring out the best way to do this...

Thanks so much for the help in advance!!