Table 2.

The advantage of PSI over PSS, $\varnothing$, HSS, and CSS in differentiating between the level of difficulty in forecasting rare or extreme event and random event.

Events	Forecasted/observed outcomes				PSI	PSS	$\varnothing$	HSS	CSS
	Yes/Yes $(\mathit{a})$	Yes/No $(\mathit{b})$	No/Yes $(\mathit{c})$	No/No $(\mathit{d})$	[-1, 1]	[-1, 1]	[-1, 1]	[-1, 1]	[-1, 1]
Rare or extreme	1	0	0	399	0.550	1.000	1.000	1.000	1.000
Random	193	0	0	207	1.000	1.000	1.000	1.000	1.000