# Understanding Strength and Correlation in Random Forest

In the original paper of Random Forest, the author introduces a concept of strength and correlation. In the appendix section, a step by step guide to calculating these values are given for the bootstrapping case. I have few doubts in this section.

1. What does $$sd(\theta)$$ signify? (equation A2).
2. As suggested by this paper, how the variance of margin is the correlation of two trees? From RF paper the equation of correlation is given by

$$\bar{\rho} = \frac{var(margin)}{(E_{\theta}(sd(\theta)))^2}$$

where $$\theta$$ is a tree in a random forest.