The group, who hold senior academic positions at Glasgow, Heriot Watt and Edinburgh universities, have told Holyrood's Culture committee they are concerned with proposed changes to the question on sex, claiming it may reduce the ability of statisticians using Census data to "capture sex-based discrimination and disadvantage".
The Committee will today hear evidence on the Census Order from the National Records of Scotland (NRS) on the testing of guidance on how Census questions should be answered.
There has been controversy over the sex question, as transgender people believe they should be able to answer according to the gender in which they live, rather than the sex they were born.
They point to guidance for the 2011 Census which had said, for the first time in the 218-year history of the data collecting exercise, they could answer the question as their lived gender and say any move away from this would be "rolling back trans rights".
However there have been calls by policy makers, statisticians and women's organisations to ensure the sex question remain as a biological binary one - unless a transgender person has a Gender Recognition Certificate which legally recognises they have changed gender.
And in their letter, the academics say they are unaware of any consultation on the 2011 guidance, and that therefore it "cannot be seen as a precedent for what is being proposed now."
The NRS has yet to decide on the final guidance, but it will have to be approved by MSPs as part of the Census Order. However a voluntary question on people's trans status, including if they identify as non-binary, will be asked for the first time after it was approved by the Scottish Parliament earlier this year.
Professors Nick Bailey, Suzanne Fitzpatrick, Cristina Iannelli, Sarah Johnsen, Susan McVie, Morag Treanor and Drs Jo Ferrie and Beth Watts, say they are writing as a group of "social science researchers" and "regular users of Census data and reports, as well as data and reports from a range of household surveys which are methodologically reliant on the Census."
They say that the believe it is "important that the Census is able to provide statistics on the lives of trans and non-binary people, to measure the size of these groups and to identify the scale of disadvantage and discrimination they may face in education, employment, health and other areas of their lives", and welcome the proposed voluntary question on trans identity.
They add that they support the decision to retain a binary question on sex, but that it needs to ask "about legally-recognised sex, rather than self-identified".
"With a self-identification approach, our ability to monitor sex-based discrimination and disadvantage would be reduced, and to a degree which we cannot assess since the trans identity question is voluntary," they say.
"The evaluation of any change to the Census sex question guidance needs to take into account the impact on our ability to measure sex-based discrimination and disadvantage. The evaluation should not be limited to issues of the public acceptability of any new question or guidance, or impacts on response rates.
"The Census has a unique importance in the statistical system. It is the only source providing full coverage of the population on such a wide range of aspects of social life and therefore it is uniquely well-placed to provide information on smaller population groups. At the same time, it is the foundation on which many other statistics about our society are built.
"When we conduct sample surveys such as the Scottish Household Survey, the Scottish Health Survey, or the Scottish Crime & Justice Survey, we know that some groups are more likely to respond than others. We therefore correct or ‘weight’ those surveys so that they give a more representative picture by ensuring that they match Census-based estimates of the population age-sex structure. Changes to the Census question on sex therefore have implications for many other statistical sources."
They add: "In putting forward these views to the Committee, we are mindful that some trans and non-binary people may regard it as unpleasant, intrusive or upsetting to be asked about their legal sex where that is not the same as their lived identity.
"We would respectfully point out that there are legitimate reasons for asking for this information: we hope that the clear separation of legally-recognised sex and trans identity will enable the Census to provide robust data on inequalities in relation to both."
Professor Susan McVie, chair of quantitative criminology at Edinburgh University's School of Law and a member of the Scottish Government's Board of Official Statistics in Scotland, has already written separately to the Committee raising her concerns. She has said: “I think that the General Register Office for Scotland got it wrong when it redesigned the census in 2011 and conflated sex and gender identity into one question. We are now trying to disentangle those things. Arguably, the measure of sex in the 2011 census data is not accurate.”
Last week the Scottish Trans Alliance held a three-day protest outside Holyrood aiming to raise awareness of transgender people’s concerns about the Census.
James Morton, manager of the Scottish Trans Alliance has said: “In all previous censuses, trans men and trans women have answered using their lived sex, and that has worked well. To change that would fundamentally undermine the long established practice, and internationally established human right, of recognising our lived sex.
“There is no doubt that if those who want this change to be made in the census are successful, they will move on to try to stop trans people being recognised as our lived sex in other areas such as our use of services including the NHS and education, and in government and other equality policies.”
He added: “If the census is changed in this way, it will be the first time that LGBT equality in legislation has gone backwards anywhere in the UK since the introduction of section 28 under Margaret Thatcher in 1988."