To test whether the difference between the slope of the tropic of cancer and "1" is significant, statistical test is usually needed. A common method is to carry out t-test.

For linear regression model, the estimated value of slope β can be obtained by least square method.

The specific steps are as follows:

The estimated value β of slope is obtained by linear regression model. The calculation formula of t statistic is: t = β-1√ (SE 2 * (1/n)), where se is the standard deviation of slope estimation value and n is the number of samples. If |t| is greater than the critical value, then you deny the original assumption that the slope is not equal to 1, that is, β ≠ 1. If you have multiple regression lines to compare, you may need to use more complicated methods, such as ANOVA or MANOVA analysis.