What are the methods for estimating correlation?

Correlation can be estimated using several methods, with the most common being Pearson's correlation coefficient, which measures the linear relationship between two variables. Spearman's rank correlation coefficient is another method that assesses the strength and direction of monotonic relationships based on ranked values. Additionally, Kendall's tau is used for ordinal data to measure the association between two variables. Each method has its specific applications and assumptions, making them suitable for different types of data.