How can I fix round-off errors in Excel when using trendline equations?

[wjp1982]

Hi, I am attempting to find an equation to fit a curve that I have plotted in Excel. I use the trendline function and get an equation but when i place that formula in excel and with the values they are different. I have attached the spreadsheet to show you. The yellow columns are my original data. The blue columns are the numbers i get from the trendline equation. My R-squared value is 1.0 for both too. Any help is beneficial thanks.

 

[TheoMcCloskey]

You are most likely suffering from round-off errors. You are using the displayed coefficients in your formula, however, those displayed coefficients are only showing one significant digit.

Increase the number of displayed digits in the trendline label (right click label, select "format data labels", set Number tab, select Scientific, select number of digits - use at least three).

The displayed coefficients will reveal themselves with more precision. Use these coefficients in your formula.

 

[quicknote]

Hello,

I understand your frustration with round-off errors in Excel when using trendline equations. These errors can occur due to the limitations of computer calculations and can affect the accuracy of your results. There are a few steps you can take to minimize these errors and improve the accuracy of your trendline equation.

1. Increase the number of decimal places: By default, Excel displays only a limited number of decimal places in cells. You can increase the number of decimal places displayed by selecting the cells containing your trendline equation and adjusting the decimal places in the formatting options. This will give you a more precise result.

2. Use the LINEST function: Instead of relying on the trendline function, you can use the LINEST function to calculate the trendline equation. This function allows you to specify the number of decimal places you want in your result, giving you more control over the accuracy of your equation.

3. Increase the data points: The more data points you have, the more accurate your trendline equation will be. If possible, try to increase the number of data points in your dataset to get a more precise result.

4. Use a higher order polynomial: Sometimes, using a higher order polynomial (such as a quadratic or cubic function) can improve the accuracy of your trendline equation. This is because higher order polynomials can better fit complex curves.

Overall, it is important to keep in mind that trendline equations are only an approximation and may not perfectly fit your data. It is always a good idea to visually inspect your trendline and make sure it accurately represents your data. I hope these suggestions help you improve the accuracy of your trendline equation. Good luck with your research!