Argentina Elections: RIWI Intercept Survey Predicted That Undecided Voters Would Play Key Role

By Luan Borges

Last Sunday, millions of Argentinians visited polling stations to determine their next president. Following the unexpected results of the primary elections, in which Javier Milei from La Libertad Avanza emerged victorious, all attention was focused on the potential for his success in the first round.

However, this scenario did not materialize.

With 98.51% of ballots scrutinized, Sergio Massa (Unión por la Patria) led the race with 36.7%, of votes followed by Milei with 30%. Patricia Bullrich (Juntos por el Cambio) came in third place with 24% and is now out of the race.

Now, Argentina will face a second round on November 19th. This runoff round became necessary because none of the two conditions for a first-round decision were met (none of the candidates received 45% of the vote or 40% with a 10% advantage over the runner-up). It is important to note that voting is compulsory for all eligible voters in Argentina, except for those under 18 years of age.

What did the RIWI data show and what can we expect for the second round?

RIWI started tracking Argentina’s presidential election on August 24, 2023 with online survey results available in real-time.

On October 20, 2023, RIWI data showed that:

  • Milei led the race but was technically tied with Massa.
  • A victory for Milei in the first round would be unlikely.
  • Milei had lost ground while Sergio Massa (Unión por la Patria) had gained more support. Patricia Bullrich (Juntos por el Cambio) had remained in third place with around 17% of the voting intentions since September 24th.
  • Undecided voters were more likely to vote for Massa than Milei.

What explains this change of seats in the last two days prior to the elections? Did the data provide any indications of this scenario?

We will delve into these key insights below, but the short answer is YES.

REASON 1 – VOTING INTENTIONS: Milei had lost ground while Massa progressively gained more support, compared to the beginning of data collection.

On October 20, 2023, Javier Milei (La Libertad Avanza) led the race according to RIWI intercept survey data. However, the data also made it clear that Massa’s ascension was possible because:

  1. The data revealed that Milei had lost ground while Massa had gained more support compared to the beginning of data collection. This movement was observed as the percentage of undecided voters decreased on a weekly basis.
  2. When considering a 4% margin of error, Milei and Massa were technically tied. Milei led the race with 27% and, based on a margin of error of plus or minus 4%, could have up anywhere from 23% to 31% of the votes. Massa held second place with 23% of the votes and could have received anywhere from 19% to 27% of the votes according to the data.
  3. Patricia Bullrich (Juntos por el Cambio) had remained in third place with around 17% of the voting intentions since September 24th.

Note: Those who reported staying at home, or voting null or blank were removed from analysis.

REASON 2 – REJECTION RATES: Milei and Massa faced similar rejection rates.

According to RIWI’s online survey data, 50% of respondents reported that they were inclined not to vote or would never vote for Massa. Milei closely followed him in terms of rejection, with a 49% rejection rate.

This indicates that those who had already made up their mind would be unlikely to change their votes and gaining more support would depend on votes from undecided voters.

REASON 3 – UNDECIDED VOTERS: The undecided voters certainly played a key role in the Argentinian elections.

As of October 20, 2023, RIWI data showed that 16% of the electorate were still undecided on who they would vote for.

So what explains Massa’s victory? His rejection rate among the undecided.

Massa faced the lowest rejection rate among undecided voters. Of this cohort, 22% reported that they would definitively vote or could vote for him. Massa was followed by Milei, with 10%. This is a possible explanation as to why the Unión por la Patria’s candidate took the lead last Sunday.

What can we expect in the second round?

Run-off scenarios

RIWI tested possible run-off scenarios by asking respondents who they would vote for in a second round.

As of October 20, 2023, Massa and Milei were technically tied in a possible run-off in the second round. 34% of respondents reported that they would vote for Massa while 33% said they would vote for Milei. A quarter of respondents were undecided.

These run-off scenarios also allowed for the testing of possible voting migration.

RIWI web-intercept data shows that Bullrich supporters are more likely to vote for Milei over Massa. The graph below shows results for a run-off between Milei and Massa when considering only Bullrich’s electorate. Of this cohort, 40% said they would vote for Milei, compared to only 6% who reported voting for Massa. 16% reported being undecided and a high percentage also reported voting blank or null in that situation. 

On the other hand, Juan Schiaretti and Myriam Bregman’s voters are more likely to vote for Massa over Milei. RIWI data revealed that 70% of Schiaretti’s supporters would likely vote for Massa in a second round and 65% of Myriam Bregman’s voters would do the same.

In conclusion, the elections in Argentina will be hard-fought. According to RIWI data, the success of each candidate will depend on their ability to form alliances and gather votes from the undecided and the voters of the defeated candidates.

RIWI is looking forward to tracking the second round of the Argentina Presidential Elections and delivering key predictive insights.

Luan Borges is an expert in foreign affairs and policy research and a project manager at RIWI. Luan holds a Master’s degree from the Graduate School of Public and International Affairs at the University of Ottawa, with expertise in Latin American issues and research methods. 

For more information about RIWI’s election tracking online surveys or to access this data, send us an email at