Testing a single time-series for changing variance structure (Heteroscedasticity and Volatility Clustering) I would like to assess a single time-series for a changing variance structure that might be leading to spurious variance estimates when that time-series is used in regression. 
In my head two terms come to mind: (1) Heteroscedasticity and (2) Volatility Clustering
Here are my related questions on this:


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*(True/False) Heteroscedasticity is related to non-constant variance of the errors while Volatility Clustering is related to non-constant variance of the levels of the time-series. As such Heteroscedasticity can only be tested for using residuals from a regression. Variance Clustering on the other hand could be tested for on the levels themselves without the need for regression. 

*How could I test an individual time-series for Volatility Clustering?

*Can Volatility Clustering lead to spurious regressions? If so is this effect enacted through inducing Heteroscedasticity in the regression?

 A: 1. I would say, heteroskedasticity can characterize original series, too. Suppose the variance of the original series was $\sigma_1^2$ from time $t_1$ to $t_k$ and turned to $\sigma_2^2$ since $t_{k+1}$. I would call that heteroskedasticity. Conversely, volatility clustering can characterize model residuals as well as the original series.
2. A popular specific type of volatility clustering is autoregressive conditional heteroskedasticity (ARCH). There is a Lagrange multiplier test known as ARCH-LM test.
3. The question is quite broad; let us consider the base case. Recall that OLS estimates are consistent (even) under heteroskedasticity. Consider two variables $x$ and $y$ that are linearly independent and mean-stationary but one or both of them have volatility clustering. The OLS estimate of the slope coefficient from a regression of $y$ on $x$ should (still) converge to zero as sample size increases. Aside from the base case, I cannot quickly come up with a situation where volatility clustering alone would yield spurious correlation between two linearly independent series (I do not claim it is impossible, but I do not see how it could work).
A: 1) Heteroscedasticity is related to non-constant variance of the errors GIVEN that Volatility Clustering does not exist or has been remedied via Level Shift Detection Procedures ( Intervention Detection Procedures ) and model parameters are found to be inavariant over time and that other error mean-adjustment procedures have been used as necessary.
2) Given that you have accounted for autoregressive structure AND anomnaly detection such as Pulses , Seasonal Pulses , Time Trend changes , parameter changes over time and either Box-cox transformations of deterministic error variance cjanges THEN if it can be proven that there is one pr more level/step changes then you can conclude about Level Changes  
3) Lots of things can lead to spurious regression.
