# Series Filter The Series Filter model partitions the full historical asset sample conditioned on the time series properties of a single reference asset within the portfolio. ![Series Filter Model Parameters](/files/-MEyCEwuPPf8Fu4aZqQi) For example, a client can use this risk model to test the hypothesis that the correlation between an asset pair increases when the S\&P 500 has a negative return. The investor must first specify which asset is the reference asset. Second, the investor must specify the threshold, or filter, to apply. The WPA allows users to specify filters in return or standard deviation units. Using the model parameters, the WPA estimates risk and correlations based on the sub-sample of asset returns. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://wpahelp.windhamlabs.com/expected-risk/series-filter.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.