'primary indicator' is correct and usable in written English.
For example, "The market's ability to absorb imports is a primary indicator of economic health."
Using race as the primary indicator of criminal activity is a lazy substitute for looking for real clues.
Consumer spending, which economists often look to as a primary indicator of recovery, grew 2 percent.
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.
"We believe the capacity for empathy is the primary indicator of how successful volunteers will be in building strong relationships with their clients," explained Lodal.
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.
The primary indicator in many Asian economies compares prices with those of a year earlier, not those of the previous month, as is common in the United States and Europe.
Hence, explosive signatures represent the robust primary indicator of landmines.
No matter what your board says, remember revenue is NOT the primary indicator; it is simply an indicator.
High wetness state levels can be considered as a primary indicator for potential river flooding.
It is a primary indicator of suitability of water for consumption.
