RIO DE JANEIRO, Sept 25 (Reuters) - Brazilian President Dilma Rousseff and her main challenger Marina Silva are running neck and neck if the October presidential election goes to a runoff, according to a poll published on Thursday.
Rousseff garnered 42 percent of voter support in an expected runoff while Silva had 41 percent, according to a survey by pollster Vox Populi. The difference is statistically insignificant based on the poll's margin of error.
The previous Vox Populi poll released on Tuesday, which was commissioned by TV Record network, showed Rousseff with a seven-point lead in a runoff, beating Silva by a 46 percent to 39 percent margin.
Vox Populi polls are not as closely watched by political analysts as those by bigger research firms Datafolha and Ibope, which are more frequent and survey more potential voters.
If no candidate wins a majority of valid votes in the Oct 5 first round, there will be a second round between the top, two vote winners on Oct 26.
In the first-round vote survey, Rousseff's support was 38 percent, down from 40 percent in the previous Vox Populi poll on Tuesday. Silva's support rose to 25 percent from 22 percent. Support for centrist candidate Aecio Neves was the same at 17 percent.
The Vox Populi poll surveyed 2,000 voters on Sept. 23-24 and has a margin of error of plus or minus 2.2 percentage points. It was commissioned by the Carta Capital magazine and the results were posted on the news weekly's website. (Reporting by Jeb Blount; Writing by Anthony Boadle and Jeb Blount; editing by Andrew Hay)