The Iowa Electronic Markets (IEM) is the oldest active prediction market and one of a handful of platforms where U.S. persons can bet on American politics. We’ve previously looked at IEM and a few of its iterations over time.
One thing IEM does not do well is make the data easily accessible. Below is an IEM Presidential election market data dashboard from 2000 to 2020. You can filter share prices by:
- Vote share (VS) and winner-take-all (WTA) markets for each election.
- Contracts offered for that market: typically, REP and DEM, but occasionally other options
- Data ranges
Three prices are visualized:
- The “Low Price” and “High Price” range on a vertical line.
- “Last Price” as a horizontal line.
Below are the Market Codes, Market Titles, and Prospectus for Presidential markets since 2000. Market Code links take you to the respective prospectus, which details the specific contracts offered in that market.
| Market_Code | Full_Title |
| PRES00_VS | 2000 U.S.Presidential Vote Share |
| PRES00_WTA | 2000 U.S. Presidential Election Winner-Takes-All Market |
| Pres04_VS | 2004 Presidential Election Vote Share Market |
| Pres04_WTA | 2004 U.S. Presidential Winner Takes All Market |
| PRES08_VS | 2008 US Presidential Vote Share Market |
| PRES08_WTA | 2008 US Presidential Election Winner-Takes-All Market |
| PRES12_VS | 2012 US Presidential Vote Share Market |
| PRES12_WTA | 2012 US Presidential Election Winner-Takes-All Market |
| PRES16_VS | 2016 US Presidential Vote Share Market |
| Pres16_WTA | 2016 US Presidential Election Winner-Takes-All Market |
| PRES20_VS | 2020 U.S. Presidential Vote Share Market |
| PRES20_WTA | 2020 US Presidential Election Winner-Takes-All Market |
| Pres24_VS | 2024 U.S. Presidential Vote Share Market |
| PRES24_WTA | 2024 U.S. Presidential Winner-Takes-All Market |
There are a few caveats with the above dashboard:
- IEM prices are three decimal places whereas the dashboard rounds to the nearest hundredth.
- In the 2004 Vote Share Market (PRES04_VS), candidates were offered by name rather than party.
- In days with no activity, (that price was listed as 0 for the day) the previous non-zero price was forward filled.
- Some of the data is messy; there are places where the Last Price is greater than the High Price (or lower than the Low Price).
You can directly check market price data for yourself on IEM here.
In the future, it would be interesting to add pre-2000 Presidential election market data, including the 1988, 1992, and 1996 Presidential elections.