Nielsen Media Research Asia-Pacific managing director, Forrest Didier, said Overmyer resigned after a difficult period with the agency, which included its loss of the A$2 million (US$1.1 million) metropolitan TV ratings measurement account.
"Helen has been with Nielsen Media Research Australia for over five years and in the last 12 months has overseen the Australian media business through some challenging times in advertising expenditure measurement, television and radio audience measurement and Panorama multimedia businesses, Didier said. Overmyer will stay in her post until a replacement is found.
In the interim, Didier said he would be actively involved in building the agency's momentum and "bringing new energies to the challenges facing the business in Australia".
Marketing and communications manager, Warren Gillmer, said media speculation that Overmyer's replacement would be drawn from America was "nonsense".
"Nationality is irrelevant, Gillmer said.
"But it would be ideal if we had a suitable candidate from the Australian market."
Nielsen is in the midst of a pitch to retain the lucrative radio ratings contract, and the pay-TV contract which may be merged with the free-to-air measurement contract.
Meanwhile, Tom Markert remains head of sister Nielsen outfit, AC Nielsen.
AC Nielsen also recently appointed Travyn Rhall as managing director of its customised research services.
Rhall is currently based with Nielsen in New York.
