Ask a data guru what they want more than anything, and they'll probably say: more data.

To put it crudely, the more samples you take and the longer you spend gathering data, the more useful the results become. Hopefully all of this leads to better decisions.

But therein lies a problem, especially when it comes to collecting data on education. It can be decades before data from students and schools begins to paint an accurate picture. 

For example, in order to understand data collected from a cohort of P1 pupils, researchers will need similar data from a separate cohort. And in order to understand how students' early primary school experiences impact their time after, you'll need at least two groups of students who have progressed from P1 to high school.

It can be challenging to create a sense of urgency for policymakers up for election every few years and for families whose children will be out of the system before the data they helped collect is the most useful.

Lindsay Paterson, professor emeritus of education policy at Edinburgh University, said that it can take at least two decades for data to become useful.

"A 20-year horizon seems to me to be the minimum time at which properly thought-through data can have a real impact on our understanding of the education system and of our evaluation of policies to change the education system."

He spoke as one of the authors of a new paper about the lack of useful data about Scottish education and how it limits decision-making on reform. 

Again, 20 years feels like a long time for parents and politicians, and climate activists can attest to the challenges of convincing people and elected members to make changes that won't pay off until they've died or left office. 

That long timeline creates two equally problematic tendencies.

First, with plenty of pressing economic and social issues, it's easy to put off enacting a new survey or study that we know won't pay off in full for 20 years. 

But if the wheels are set in motion, it can also be tempting to sit back and take the excuse to remain dormant for 20 years until we have all the information we need.

Part of what Prof Paterson and the other members of the lobbying group Reform Scotland's education arm are calling for is a way to help students and families feel that they are taking ownership of the education system. It's also about accountability for politicians who love to make big, headline grabbing claims but all-too-often have little interest in being held to their grand, election-friendly promises.

And let's just be absolutely clear: education data in Scotland is hugely problematic. We collect lots of it, but in so many cases it is of questionable value, and in some instances is downright misleading. The more you know about how to read it, the less useful it often appears.

Literacy and numeracy stats are based on individual teacher judgments that are then negotiated and aggregated. The result is that we don't really know how well pupils across the country can read, write and 'rithmetic. School leaver data tells us who goes to things called 'positive destinations', but the breakdowns are either entirely lacking in detail or, in the worst case, hiding major socio-economic divides, making the overall publication of limited actual use.

But it's not just what's missing - it's also what we've lost. The SNP decision to scrap the excellent and well-respected Scottish Survey of Literacy and Numeracy - which was sacrificed for entirely political reasons because it threatened to produce data that the government didn't like - is a particularly good example, robbing us of both annual and long-term data about the state of education provision in the country.

Reform has been the buzzword in Scottish education for years now. Whether spurred by perceived system failures or by changes in what students, employers and families need, the majority of stakeholders in education agree that something needs to change.

And yet, change has ground to a halt, despite nearly £1m spent on education reviews and consultations in recent years. 

Part of the issue is that decision-makers can't fully agree – or commit – on the direction we should be headed. However, an equally problematic concern is that in cases where we can identify a problem, we are often missing the information we need to put together a lasting solution.

And getting it could take years.