The phrase "a proportion less than" is correct and usable in written English.
It can be used when discussing quantities, statistics, or comparisons where one value is smaller than another.
Example: "The study found that a proportion less than 20% of participants reported experiencing side effects."
Alternatives: "a fraction smaller than" or "a percentage below".
As part of its financial settlement with the chancellor in July, the BBC agreed to take on a proportion (less than 25%) of the cost of providing free TV licences to the over-75s between 2015 and 2020 (Letters, 29 December).
For example, the federal deficit for fiscal year 2013 is expected to be $642 billion, a proportion less than half as large as in the fiscal year 2009 budget, at the height of the recession.
If the detection time is variable, tracing may be effective even if a proportion less than 1−1/R 0 pre is traced (SARS if δ<0.4, panel 3C).
More than a million refugees and migrants arrived in Europe in 2015, but that's a tiny proportion – less than 0.2% – of the EU's total population.
Germany has taken more than 40% of the Syrian refugees who have reached Europe (and those, it should be recognised, are only a tiny proportion, less than 5%, of the total number of Syrians who have fled the civil war).
Only a small proportion (less than 1%) of human cord blood cells was nestin positive (Figure 2, A1 A3).
Nevertheless, abortions based on medical indications appear to constitute a small proportion (less than 3%% in 2010).
Each of the significant predictors of beliefs identified only explained a small proportion (less than 5percentnt) of the overall variance associated with the belief variables.
Of the final sample of 2,229 respondents, only a small proportion (less than 3% of the sample) failed to provide valid responses for 2 of the variables in the present analyses.
To minimize the impact of these gaps on the outcome of our analyses, we used two alignment algorithms (ClustalW and Bali-Phy) and excluded regions where only a small proportion (less than one-third) of sequences shared insertions.
It is now known from natural history studies performed using frequent MRI scanning that clinical relapses represent only a small proportion (less than 20%) of CNS inflammatory events, indicated by the presence of contrast enhancing lesions [ 2- 4].
