Cook's distance chart threshold

[aravindhebbali]

User should be able to choose from the below formulas:

• 4/n
• 4/(n - k - 1)
• ~1 (as per Cook's original paper)
• 1 / (n - k - 1) where k = number of regressors
• 3 * mean(vectors of values of cook's distance)
• Critical value of median from F-distribution

n - number of observations k - number of predictors

for calculating the threshold in

• ols_plot_cooksd_bar()
• ols_plot_cooksd_chart()