A study into the Scottish election voting fiasco has found the highest proportion of rejected constituency votes came in the most deprived areas.
The probe, by the University of Strathclyde, was triggered by the chaos which saw more than 140,000 spoiled papers in the May poll.
It also found that more votes were discounted in areas where there were a larger number of list candidates.
The Electoral Commission has already launched an inquiry into the problems.
The Strathclyde report said a total of 85,643 constituency and 60,464 list votes were rejected on election night.
That figure was a massive increase on the 15,000 spoiled ballots in the first Holyrood election in 1999.
The study, carried out by the university's department of government, claimed to have uncovered "distinct and disturbing evidence" into what went wrong.
It found that more rejections came in areas with a greater degree of social deprivation. It pointed out that 633 votes were discounted in the Stirling constituency, but the figure rose to more than 2,000 in Glasgow Shettleston.
Other problems, the report added, came as a consequence of altering ballot design to deal with larger numbers of candidates standing on the regional list.
Prof James Mitchell, who carried out the study with Dr Christopher Carman, said: "No constituency was immune from the rejected ballot problem - it was pervasive and infected all Scottish constituencies.
"We found the greater the degree of social deprivation in a constituency, the higher the rate of rejected ballots.
"This finding may highlight a need for a greater degree of clarification of the voting system prior to large-scale changes to ensure everyone knows how to cast their ballots properly."
Some of the problems may have stemmed from the decision to introduce a single-paper ballot design which included both the regional list and first-past-the-post votes.
On the regional list vote, Prof Mitchell added: "It appears that as the number of parties increased, the ballot papers became pressed for space, leading to fewer and less clear instructions on how to vote.
"Our research indicates the different rules or ballot design used in different regions had a very clear and distinct influence on the number of rejected ballots."
A copy of the study's findings has now been sent to the Electoral Commission, which appointed international elections expert Ron Gould to head up its review.
The Strathclyde report's authors said action was needed to restore public confidence in the Scottish election system.