OTTAWA — Efforts to keep the last federal census on time and within budget could affect accuracy of the resulting numbers, the federal auditor general warned Tuesday.

In her latest report, Sheila Fraser said that Statistics Canada generally managed the 2006 census successfully.

But she said the agency's decision to stop field collection activities at the end of August 2006 was a tradeoff between accuracy and the cost of completing data-gathering as well as the need to stay on schedule.

The national response rate to the 2006 census of population was 96.5 per cent, slightly lower than the 98.4 per cent achieved in 2001 _ consistent with general trends in surveying.

There were two reasons cited: a higher-than-expected number of houses failing to return a completed questionnaire, and challenges recruiting and training field staff in some locales.

Governments use census data to plan programs and make decisions.

Fraser's report says that while 96.5 per cent is a high response rate by survey standards, even small increases in failure to respond "could have an impact on data accuracy for small geographic areas and sub-populations.''

However, Fraser did not examine the resulting census data and therefore could not gauge possible effects.