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I have a graph below where I put my data into an Excel sheet and try to obtain a linear equation for it using the trendline function. The equation that I obtained shows that the y-intercept is -105.09. However, if I really extrapolate the line until it crosses the y-axis, I don't think I will cross at -105.09. This is really weird and I think I overlooked something. Can someone please explain this to me?

enter image description here

ryang
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mike
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    This seems to me more like a stackoverlfow question. Please include the excel file in your question or a minimal reproducible example – Gábor Pálovics Oct 03 '21 at 08:52
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    Can you show the specific extrapolation that you did which disagrees? Note that the left-most $x$ value in the graph is $x=100,$ so the $y$-axis is quite off the left side of the screen. – Thomas Andrews Oct 03 '21 at 08:55
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    @Thomas' comment has just answered your (possibly duplicate) Question. I consider this a Mathematics rather than Programming question, as it is about how to properly/carefully read graphs (checking the axis labels & truncation, etc.). His comment should be converted to an Answer. – ryang Oct 03 '21 at 09:07
  • If you apply $y=0.8867x-105.09$, then when $x=120$ you get $y=1.314$, while when $x=200$ you get $y=72.25$. This seems consistent with the dotted line on your chart. Where do you think the intercept should be (i.e. $y$ when $x=0$ on the regression line)? – Henry Oct 03 '21 at 09:30
  • @RyanG the only reason I haven’t posted an answer is that I’m not sure that is the mistake OP is making. It was the first possible one that jumped out at me, but the term “extrapolate” is vague. – Thomas Andrews Oct 03 '21 at 09:46

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