I I have an Excel scatter chart with x and y values. I set the logarithmic scale in x-axis and y-axis.
When I add a linear trend line to the graph, the line is not linear but appears like a curve.
How can I make a linear trend line on a logarithmic-scaled chart?
Sample data:
x:
18449
22829
25395
36869
101419
125498
208144
2001508
14359478
17301785
y:
269,09
273,89
239,50
239,50
175,13
176,73
151,94
135,15
131,55
121,551 Answer
Adding a Power Trendline seems to have worked. tusham has kindly saved me the trouble of explaining why:
The power trendline is given by y=c*x^b. Believe it or not, you can use LINEST to calculate the parameters. Here's how.
Take the log of the above equation to get ln(y)=ln(c)+b*ln(x). This is a linear equation!
and
A log-log display of the data doesn't change the underlying analysis. If you plot a bunch of X,Y pairs and ask for a power trendline, you will get the same result irrespective of whether the plot shows either or both of the axes on a log scale.
