Table 3. List of early-warning signals and estimators.

EWS	Estimator
Mean	${\displaystyle {\widehat{\mu }}_t=\sum _{s=t_0}^t{\displaystyle \frac{e^{-\kappa (t-s)}{C}_s}{Z}}}$
Variance	${\displaystyle {\widehat{\sigma }}_t^2=\sum _{s=t_0}^t{\displaystyle \frac{e^{-\kappa (t-s)}{(C_s-{\widehat{\mu }}_s)}^2}{Z}}}$
Coefficient of variation	${\widehat{\text{CoV}}}_t={\displaystyle \frac{{\widehat{\sigma }}_t}{{\widehat{\mu }}_t}}$
Index of dispersion	${\widehat{\text{IoD}}}_t={\displaystyle \frac{{\widehat{\sigma }}_t^2}{{\widehat{\mu }}_t}}$
Skewness	${\displaystyle {\widehat{\text{Skew}}}_t={\displaystyle \frac{1}{{\widehat{\sigma }}_t^3}}\sum _{s=t_0}^t{\displaystyle \frac{e^{-\kappa (t-s)}{(C_s-{\widehat{\mu }}_s)}^3}{Z}}}$
Kurtosis	${\displaystyle {\widehat{\text{Kurt}}}_t={\displaystyle \frac{1}{{\widehat{\sigma }}_t^4}}\sum _{s=t_0}^t{\displaystyle \frac{e^{-\kappa (t-s)}{(C_s-{\widehat{\mu }}_s)}^4}{Z}}}$
Autocorrelation at lag δ	${\displaystyle {\widehat{\text{AC}}}_t=\frac{1}{{\widehat{\sigma }}_t{\widehat{\sigma }}_{t-\delta }}\sum _{s=t_0}^t{\displaystyle \frac{e^{-\kappa (t-s)}(C_s-{\widehat{\mu }}_s)(C_{s-\delta }-{\widehat{\mu }}_{s-\delta })}{Z}}}$