Linear trend function: 5 year increment

[Angie]

I am using the trend function to trend utilization rate. My known x's are
the utilization rate, and my know y's are the years. I have data on an
annual basis for 2000-2015, and then it jumps to 5-yr increments for 2015 to
2030. Can I just trend this out despite the increment change, or do I need
to make an adjustment. I was trying to manually calculate y=mx +b, but
couldn't quite figure out how to manually calculate this given that I have a
year, and not an actual number for my y value. So, for example, if
utilization for 2000 is 200, would you use the following to calculate the
utilization for 2001: 2001=((2001-2000)/(x-200))200 + 2001

Thanks!

 

[Gary''s Student]

Consider treating the years as the x-variable and utilization as the
y-variable. Becasue the years are evenly spaced within ranges, the
interpolation or extrapolation may be easier.

 

[Angie]

Thanks Gary,

I tried that, but the trended data comes back much higher than what I would
expect, so I don't think I can do that in this case.