This article is part of our The Z Files series.
The MLB season will likely be delayed at least two months. One of the repercussions is that the coldest two months will be excluded from the schedule. Granted, if the regular season extends past September, cooler weather will return. That said, one of the possibilities is for the extended schedule to be contested at neutral sites. Not to mention, there's a chance the whole season (whatever that ends up looking like) is played in warm weather sites. Regardless of what happens, losing April and May has a potentially big impact on park factors when they're broken down on a monthly basis.
The park factor calculation is designed to flesh out all biases, so the sole factor being measured is how the venue plays. As has been discussed previously, the bias isn't eliminated, but until alternate means of computing park indices are perfected (they're coming, likely based on Statcast data), using the indices as conventionally determined is better than not using them.
Park factors for any metric can be calculated. Runs, hits and homers are the most common examples, with strikeouts and walks underrated in their utility. Many assume runs and homers track proportionally. As will soon be illustrated, homers and runs are mutually exclusive. Hits and runs correlate better and many venues favor homers but suppress hits, and vice versa.
In order to reduce the variance from the residual bias, park factors are expressed as a three-year average. When a venue undergoes a major renovation, or a team moves to