Professor John Curtice of Strathclyde University said that of the 48 MSPs newly elected in 2011, only one had ever served in the Scottish Parliament before.
In 1999 – the first Scottish Parliament elections – there were vastly more experienced figures who had served for years at Westminster, such as Donald Dewar and Henry McLeish.
The new intake saw 30 new SNP MSPs arrive at Holyrood and 15 new Labour members.
Prof Curtice claimed the lack of experience on the governing party’s back-benches and in the opposition ranks meant the SNP would be held to account less than if more experienced parliamentarians had been elected.
He said the loss of high-profile Labour figures such as former health minister Andy Kerr and ex-justice spokeswoman Pauline McNeill on election night had weakened the opposition.
However, Prof Curtice said the Labour intake included some talented figures, such as North East MSP Jenny Marra, who has been widely viewed as one of her party’s top performers at Holyrood since the election.
He said: “Although there will be experience on the SNP backbenches, the large number of new MSPs elected mean it’s inevitable that there are lots of inexperienced figures also. Overall, it’s the most inexperienced parliament since 1999.
“The loss of some of Labour’s big figures means the party has less experience than is needed. It’s bound to mean that the opposition is less effective. Of course, at the same time, there have been one or two new people elected as Labour MSPs who’ve made an impact, like Jenny Marra, but we’re talking about small numbers at the moment.
The Electoral Reform Society Scotland report said: “Given the change in the partisan balance of the parliament, it was of course inevitable that the newly elected body would have a relatively large number of new and thus inexperienced MSPs.
“In the event, no fewer than 48 of hose elected in 2011 fell into this category, though one had previously been a MSP in an earlier parliament, while two had previously been MPs at Westminster. This figure is higher than the equivalent figures in both 2007 (41), of whom six had been MSPs between 1999 and 2003 and three were former MPs) and 2003 (just 26).”
Prof Curtice’s report said Labour suffered the loss of senior figures by not allowing people to stand as both list and constituency candidates, in the way the SNP had done. The report said: “More than half of its incumbent constituency MSPs crashed to defeat, and, lacking a place on the party’s list, saw themselves replaced in the chamber by parliamentary novices who unexpectedly won on the list.”