When I graph my slope (3000) and negative y-intercept (-0.001100) using Excel, why do I get different values for the slope and y-intercept in my trendline equation? Did I graph it wrong?
No, you did not graph it wrong. The reason you are getting different values for the slope and y-intercept in the trendline equation is due to the way Excel calculates trendlines.
When Excel adds a trendline to a graph, it performs a linear regression analysis to determine the best-fit line for the data. Linear regression involves finding the line that minimizes the sum of the squared differences between the predicted values and the actual values.
In your case, the slope of your trendline in Excel might be slightly different from the value you entered (3000) due to the nature of the regression analysis. Excel attempts to find the best-fit line that minimizes the overall error and provides the most accurate representation of the data.
Similarly, the y-intercept value in the trendline equation might not match exactly with the value you entered (-0.001100). This difference can occur because Excel rounds the values in the trendline equation to a certain number of decimal places, usually four.
To confirm the exact values of the slope and y-intercept in your graph, you can inspect the trendline equation directly. Right-click on the trendline in your graph and select "Format Trendline." Then, choose the "Options" tab, and check the box that says "Display equation on chart." The equation displayed will show you the specific values of the slope and y-intercept Excel has calculated based on your data.
Note that even though there might be slight differences in the trendline equation values calculated by Excel, these differences are typically negligible and should not significantly impact the overall interpretation of your data.