  Ensembles of random legislative districts are a valuable tool for assessing
whether a proposed district plan is an outlier or gerrymander. Expert witnesses
have presented these in litigation using various methods, and unsurprisingly,
they often disagree.
  Recent open source methods now permit independent validation of expert
witness testimony. Here, we compare ensembles for the Pennsylvania House and
Congressional districts calculated using "Redist" and "Gerrychain" further
incorporating constraints restricting county and municipal boundary splitting,
as required by Pennsylvania for legal plans.
  We compare results to expert witness testimony submitted by Republican and
Democratic parties. We confirm some of the testimony but could not reproduce
all of it, struggling with metrics based on a heuristic "sum of votes index"
rathern than a straightforward average of metrics across multiple elections. We
recommend against relying on analytics based on summing votes from multiple
elections to create vote incides and derivative metrics as these are inherently
poorly behaved. To promote transparency, we recommend that where possible,
expert witness testimony be based solely on publicly available election data as
opposed to proprietary data closely held by political parties.
