Are the Gameday data as good as STATS or BIS data?
No. I have already discussed the problem of Gameday giving the location of where the ball is picked up instead of where the ball lands on base hits. But in addition some fielding locations are missing and others seem to be clearly in error. The Gameday data had to be normalized because of differences in the hit recording diagrams and the normalization process will create errors. Won’t this lack of quality in the Gameday data make the BZM numbers much less accurate than UZR or Plus/Minus? Even though the raw Gameday data are less accurate than BIS or STATS raw data, it is still very close. The omissions and errors that I mentioned above are present in only about 1 percent of the raw data and are less in the most recent years. All three data sources depend on human observation and no one knows which of the human observers has been most accurate in the data collection. The variation caused by errors in the Gameday data appears to be very small compared to the variation caused by the human
