The phrase "a decrease in the proportion of" is correct and usable in written English.
You can use it when discussing statistical changes or trends, particularly in contexts related to demographics, economics, or research findings.
Example: "The study revealed a decrease in the proportion of smokers among young adults over the past decade."
Alternatives: "a reduction in the share of" or "a decline in the percentage of".
Addition of HGH caused a decrease in the proportion of insulin bound to antibody.
Miliband, meanwhile, has suffered from a decrease in the proportion of people who approve of him – from 22% to 21%.
As the economy improves and more parents find work, this leads to a decrease in the proportion of pupils eligible for free school meals".
A decrease in the proportion of further education colleges offering physics may reflect the economic pressures they are under not to offer classes for small numbers of students.
The DCMS report also revealed a decrease in the proportion of working adults using public library services over the last two years, from 33.4% in 2013/2014 to 31% in 2015/2016.
Over the same period, there was also a decrease in the proportion of adults in Britain who binge drank at least once in the week before interview, from 18%to15%5%.
In the same manner that companies of all sizes are moving away from the combined CEO-Chair, all sectors have also seen a decrease in the proportion of companies with a CEO-Chair.
In the technology industry, there has been a rapid growth of Asians among professionals and, to a lesser extent, among managers, coincident with a decrease in the proportion of Whites, particularly White females.
Moreover, the imported oligoribonucleotide designed to target a pathogenic point mutation in mitochondrial DNA was able to induce a decrease in the proportion of mutant mitochondrial genomes.
If one thinks about polarization in partisan terms, one would expect to see an increase in the proportions of Democrats and Republicans and a decrease in the proportion of independents.
Similarly, flow cytometry analysis of aldehyde dehydrogenase (ALDH) activity, a well-characterized marker of colon CSC subpopulations45, demonstrated a decrease in the proportion of ALDH-positive cells upon XMD8-92 treatment (p < 0.05) (Fig. 3c).
