I've given the league positions above...

This is pretty much what that graph would look like though:
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You could compare these two years
2005 2nd 83 8
2006 4th 67 24
And say there's a clear decline but then 3 years later it was:
2009 4th 72 18
And then last year:
2017 5th 75 18
That's the first year we finished outside the top 4 and it was only by 2 points. We don't know yet whether that marks the start of a period outside the top 4 or was a blip.
There has been a decline in terms of quality of our play, in terms of league position and points total, not so much.