The phrase "a clear decline" is correct and usable in written English.
It can be used to describe a noticeable decrease in something, such as performance, quality, or numbers.
Example: "The report indicated a clear decline in sales over the last quarter."
Alternatives: "a noticeable drop" or "a significant decrease."
The slope is gentle but testifies to a clear decline.
Since the 1960s the nutrient load of Lake Balaton has increased significantly, causing a clear decline in water quality.
A clear decline was evident: In 2005, 19.8 percent of wounded American soldiers died from their injuries.
Soviet public-health statistics show a clear decline from 1965 to the early 1980s, with rising deaths from circulatory diseases (because of poor diet, smoking and, especially, drinking).
There is generally a close correlation between annual precipitation and elevation, and there is a clear decline in annual rainfall toward the northwest.
Even so, the Minnesota Internet Traffic Studies (MINTS) project, which Dr Odlyzko heads, shows a clear decline in traffic growth compared with previous years.
That's a clear decline from the 1990s and the early 2000s, when more than two-thirds of Americans supported such a ban.
Research by the Early Warning Project for example, has shown a clear decline in mass killings in wars and conflicts since 1992.
Between 2004 and 2010 there was a clear decline in the proportion of the public who rated standards of conduct as either 'quite high' or 'very high'.
Children from homes that were demolished showed a clear decline in mental health, with classic signs of trauma: withdrawal, depression and anxiety.
In feed domain the H2 molar fraction showed a clear decline in the axial direction from feed inlet to retentate outlet by 45.34% (for the case of feed fraction 50% H2 and feed flow rate 100 N ml min−1).
