It claims that nearly half of Scots who do not regard themselves as British in any way still wish to remain in the UK.
The study by the Scottish Centre for Social Research (ScotCen) also found widespread optimism about the impact of independence did not translate into majority support for leaving Britain.
The analysis, How will Scotland answer the referendum question?, was co-authored by Professor John Curtice of Strathclyde University, the country's leading polling expert.
The findings are based on the long-running Scottish Social Attitudes Survey, which monitors changing public opinion on a range of topics.
According to the latest figures, just 53% of those who describe themselves as "Scottish, not British" support independence.
The category accounts for about one-third (29%) of Scots and is the group most likely to back a split.
The latest social attitudes survey put overall support for independence at 32%, up from 23% in 2010 and the highest level since 2005. It also showed people were more inclined to be optimistic than pessimistic about an independent Scotland's prospects on a range of issues , including 51% who believed leaving the UK would give the country a stronger voice in the world.
However, there was less optimism about the economy.
A total of 34% of people said independence would make the Scottish economy stronger, compared with 29% who believed it would become weaker.
The report said: "As yet, a majority of people in Scotland are not convinced that independence would be of positive economic benefit.
"People's willingness to support independence does not solely depend on whether or not they have a strong sense of Scottish identity. It would appear that the eventual outcome of the referendum could well turn on which side is thought by the Scottish public to have the better of the economic argument ."
Scottish Liberal Democrat leader Willie Rennie said: "The report shows that the economy is the key factor but the SNP simply haven't shown a credible case, despite all the time they have had to prepare one.
"Strikingly, most people think that taxes would go up in an independent Scotland."
The Yes Scotland campaign seized on figures showing that, when presented with a range of constitutional options, 43% of Scots wanted Holyrood to take "all decisions for Scotland".
Leader Blair Jenkins said: "A key finding of this research is that far more people hold the view that the Scottish Parliament should be taking all the decisions for Scotland."
The study follows a report this week by macroeconomic think-tank Capital Economics which warned that the UK would demand a "near veto" over an independent Scotland's budget as the price for keeping the pound.
It sparked a fresh row over the economics of independence. Alistair Darling, leader of the pro-UK Better Together campaign, said it showed "the wheels continue to fall off the Nationalist bandwagon".
SNP Finance Secretary John Swinney dismissed the research as "deeply flawed".