The phrase "a primary indicator of" is correct and usable in written English.
It can be used when discussing something that serves as a main sign or signal of a particular condition or trend.
Example: "The increase in temperature is a primary indicator of climate change."
Alternatives: "a key sign of" or "a major signal of".
Consumer spending, which economists often look to as a primary indicator of recovery, grew 2 percent.
Limnologists and hydrobiologists are attentive to the dissolved oxygen content of the water because it is a primary indicator of water quality.
The progress of such mapping in the various parts of the world is therefore a primary indicator of the status of cartography in general.
Rising margin debt was once seen as a primary indicator of financial speculation, and the Federal Reserve controlled the amount that could be borrowed by each investor as a way to damp excess enthusiasm when markets grew frothy.
In 1901, for instance, in the United Kingdom the expectation of life at birth, a primary indicator of the effect of health care on mortality (but also reflecting the state of health education, housing, and nutrition), was 48 years for males and 51.6 years for females.
It is a primary indicator of suitability of water for consumption.
Eye jerks and saccade oscillations are a primary indicator for a wide array of neurodegenerative diseases in addition to Parkinson's disease (e.g. progressive supranuclear palsy, multiple sclerosis, and cerebellar degeneration ).
After a brief introduction to the wind power energy as a reliable alternative in comparison to fossil fuel, the paper focuses on concept of natural frequency as a primary indicator in designing the foundations of OWTs.
Getting to a call within the allotted time – a major target discussed by every borough's senior management as the primary indicator of a day's successful policing – has become more important than the reason for attending the call in the first place.
In its report, the committee cited the real gross domestic product -- the value of all goods and services in the economy, adjusted for changes in prices -- as the primary indicator of a recovery.
Population size in a geographical area is the primary indicator of need [ 13].
