Turnout Rates by Type of Election (Maricopa County)
The Maricopa County Recorder’s Office has a wonderful archive of past election results going back to 2000, and local elections going back to 2003. I dug through them to find patterns in voter turnout rates. Here’s a quick tour of what I found. (Note: all turnout rates are based on a denominator of total registered voters eligible to vote in each election).
Below is the first-cut of findings. The bars reflect the full range of turnout rates by election type:

Some quick definitional notes:
- “Local” includes all election dates when only local jurisdictional elections were held, including any and all combinations of local candidate and ballot measure elections.
- “Primary” is the state primary in August (or September, in early periods) and the CD special primary in February 2018.
- “Special” includes both the CD8 special general election in April 2018 and the statewide referendum elections in May 2010 (Jan Brewer’s one-cent sales tax) and May 2016 (Doug Ducey’s land trust and pension reform measures).
- The other categories are hopefully self-explanatory.
Impact of the Permanent Early Voter List
After the County Recorders created the Permanent Early Voter List (PEVL) in the summer of 2007, turnout in local, primary and presidential preference elections increased notably. The variation within all three election types narrows when you isolate PEVL period elections:

(General and special election turnout doesn’t appear to have been affected much, if at all).
Local elections are held throughout the election cycle, in the spring and the fall, and in both odd- and even-numbered years. I was curious if local election timing affects turnout, and I found one notable dichotomy: between odd and even year elections in the pre-PEVL period. That difference seems to have vanished after the introduction of the PEVL.

Revised Chart
Here’s a final chart, showing PEVL period data only for local, primary, and presidential preference elections, but all data for general and special elections:

The ranges are all pretty narrow now, with the largest variation in turnout rates coming among local elections and midterm general elections. All other election types see turnout rates that vary only within fairly narrow bands, and suggesting turnout in those elections should be fairly predictable within a few percentage points.