When the Supreme Court struck down race-based admissions at American colleges and universities just over a year ago, many predicted US campuses would become much less diverse. But in part due to students who decide not to disclose their race or ethnicity, coupled with universities’ selective use of statistics, it is not clear how much the decision has affected diversity on campus.

As higher education institutions begin reporting the racial makeup of the class of 2028 – the first to be affected by the 2023 decision – the data is hard to interpret, confusing and inconclusive.

As a sociologist who has studied how institutions of higher education collect and report data on race and ethnicity, I have identified some factors that contribute to this lack of clarity.

Some students may not select a racial or ethnic category because they don’t believe any of the categories really fit. For example, before multi-racial students could select “one or more”, an option that became widely available in 2010, they were more likely to decline to identify their race or ethnicity. Some even boycotted checkboxes entirely.

Other students don’t view their race as important: 67% of the students who choose “race and ethnicity unknown” are white. Of these students, 33% say race and ethnicity are not a relevant part of their identity, a researcher found in 2008.

The number of students who don’t respond to questions about race or ethnicity – and are listed in the “race unknown” category – is increasing. At Harvard University, for example, the percentage of “race-unknown” undergrad students doubled from 2023 to 2024.

As the number of “race unknown” students grows, it not only becomes harder to determine a student body’s ethnic and racial diversity but also the impact of the ban on race-conscious admissions.

Some students believe their race or ethnicity will harm their chances of admission.

This is particularly true at many selective institutions, which have higher non response rates than less selective institutions, about 4% compared with 1% to 2%.

My research shows that students are even more likely to pass on identifying race or ethnicity at selective law schools, where race and ethnicity could be used among a variety of criteria for admissions before the Supreme Court ruled against that practice. An average of 8% of students at those schools chose not to identify, compared with 4% at less selective law schools.

What a university chooses to report will also affect the student body demographic data the public sees. Harvard, for example, does not report its proportion of white students.

Some institutions use statistics strategically to appear more diverse than they are. These strategies include counting multi-racial students multiple times – once for each race selected – or including international students as a separate category in demographic pie charts. The greater the number of different-coloured slices on the chart, the more demographically “diverse” an institution appears to be.

While universities may not all report their student demographics the same way in their own materials, they all have to report it the same way to the federal government – namely, to its Integrated Post Secondary Education Data System, better known as IPEDS. The next IPEDS report on characteristics for the 2024 enrolment class is expected to be released in spring 2025. Once that data is available, a better picture of how the Supreme Court’s decision has affected diversity in college enrolment should emerge.

That clearer picture might not last long. In 2027, the federal government will require colleges and universities to make changes to how they report student race and ethnicity. Among the changes is the addition of a Middle Eastern and North African category. Under the current standard, Middle Eastern and North African students are counted as white. As a result, white enrolment at some colleges and universities will appear to decline after 2027.

The new standards will also change the way universities treat Hispanic or Latino ethnicity on enrolment forms. Today, if students self-identify as Hispanic and white, they will be categorised as Hispanic. If students select Hispanic and white in 2027, they will be categorized as multi-racial. The revised categories will muddy the impact of the Supreme Court’s decision. A drop in the number of Hispanic students reported could be due to the court’s ruling. Or it may result from the new way students will be counted.

Until universities and colleges adjust to the new guidelines about collecting and reporting race – and as long as students decline to provide their racial identities – the full effect of banning consideration of race in college admissions will remain a cloudy picture at best