# Use Excel to find the similarity between functions.

#### 24forChromium

I am writing a paper and I came up with a function that uses a hypothetical relationship to predict the value of one variable at different points in time, I graphed it, and then graphed the actual readings from an experiment. How can quantitatively describe how close the two trends are? In other words, how can I quantitatively describe the amount of support the hypothetical relationship get from the experiment? See image for more ideas, predictive function gives values in blue, actual readings are orange.

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#### DrClaude

Mentor
You could perform a χ2 test. You can also calculate the R2 for your model, since you already have the value for the linear regression.

If you don't know what any of that means, you can start with https://en.wikipedia.org/wiki/Goodness_of_fit

#### FactChecker

Gold Member
2018 Award
You can get the confidence intervals for the slope and intercept of the regression line. For a given confidence level, your theoretical parameters will be in or out of the confidence interval. Just eyeballing the data, the regression line, and your theoretical line, I think there is something missing from your theory. I think it is likely to be statistically rejected.

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