"If people's worries about security of personal information were eased, the pool of online shoppers would be greater," said John B. Horrigan, associate director at Pew.
The number of US consumers who have purchased online more than doubled from 22% in June 2000 to 49% in September 2007.
Pew said that number extrapolated to 66% of Americans with Internet access having bought something online.
The research center estimated that the percentage of online buyers would be as much as three percentage points higher, or 69%, if people were not as concerned about about sending personal or credit card information over the Web.
Broadband was the most significant common characteristic of online buyers compared with non-buyers. More than three-quarters of online buying US consumers had broadband, while little more than one-half of non-buyers did.
As with many statistics, online buyer numbers can vary greatly depending on methodology. Even an average number can belie variations within a data set.
For example, in a study released this month, Eurostat found that 30% of consumers in the EU27 had made at least one purchase online. But the numbers ranged from 10% for Italy to more than 50% for the UK and Scandinavian countries.
Similarly, The Nielsen Company issued a press release about a study conducted in October and November 2007 which put the world's online purchasing population at roughly 90% of the world's Internet population.
Nielsen told eMarketer that the study was based on custom research, and involved different panels worldwide.
In order to get an apples-to-apples comparison for Canada and the US, eMarketer counted Internet users ages 14 and older when creating 2007 estimates of online buyers. Anyone within that group who had made a purchase within the past year was counted as an online buyer, resulting in a 66.3% online buyer population in the US and 55.5% in Canada.
The eMarketer numbers were very similar to Pew's, although Pew counted only adults who had made an online purchase at some point.
