Pennsylvania performs a Traditional Audit, and is moving to require Risk-Limiting Audits by November of 2021. In 2020, Risk-limiting Audits were performed in 63 of PA's 70 counties as part of a pilot project.
What is a Traditional Audit? In a traditional audit, paper ballots from a sampling of precincts are examined and recounted to make sure they match the recorded vote. Traditional audits look at small fraction of the vote. Pennsylvania requires each county to audit 2% or 2000 (whichever is less) of the votes from each county. This type of audit serves as a spot check.
What is a Risk-Limiting Audit? While a traditional audit is complete once the target number of ballots is audited, a risk-limiting audit is complete when enough ballots have been audited to ensure that the recorded election result is correct. How do auditors decide when they've "seen enough?" They use the same kinds of statistical analysis used by medical researchers or forensic investigators to calculate the likelihood that the election results are accurate. If the election is close, or there are significant errors found in the audit, the risk-limiting audit will continue adding ballots to the audit total, and can escalate to a full recount. In 2020 Pennsylvania ran a pilot risk-limiting audit, made possible by the shift to paper ballots.
Is an Audit the Same as a Recount? No. The traditional and risk-limiting audits involve recounting some ballots, but not all. And some audits check other parts of the election process, like polling place practices, or voting equipment standards. Sometimes, information found in an audit can lead to a full recount, and risk-limiting audits are designed to do this when necessary.
In Pennsylvania, an automatic recount is required in an election that is decided by less than 0.5% of the vote. If the margin is wider, a candidate may request (and pay for) a recount.