A city experiences a sudden increase in unemployment after a factory closes. Two analysts apply STL decomposition.
Analyst P argues that robust=True should always be used because it removes all abnormal values.
Analyst Q argues that robust decomposition can reduce the influence of isolated extreme observations, but a sustained economic shift may represent a meaningful change that should not automatically be discarded.
Which evaluation is most appropriate?

Question

A city experiences a sudden increase in unemployment after a factory closes. Two analysts apply STL decomposition.

Analyst P argues that robust=True should always be used because it removes all abnormal values.
Analyst Q argues that robust decomposition can reduce the influence of isolated extreme observations, but a sustained economic shift may represent a meaningful change that should not automatically be discarded.

Which evaluation is most appropriate?

Accepted Answer

Q is correct because persistent structural changes and isolated outliers should not necessarily be treated in the same way.

Answer

Neither is correct because robust weighting affects only the seasonal period.

Answer

Both are correct because robust STL guarantees accurate separation of outliers and structural changes.

Answer

P is correct because robust decomposition deletes every unusual observation before estimating the trend.

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