"a solid indicator of" is a correct and usable phrase in written English.
You can use it to describe something that is a reliable indicator or measure of something else. For example, "Test scores are a solid indicator of a student's academic progress."
The results strongly suggest that grip strength is a solid indicator of one's mental health and could be used to identify problems before other symptoms become noticeable.
Tensions between CHQ and the travelling party is almost a cliche in Australian elections - it's usually a solid indicator of which party is the losing side (although it wasn't in the 1993 election).
It demonstrates our progress and tells us where we are on the unemployment cycle, which is not only predictable, but also has historically been a solid indicator of economic health.
"We cut earnings per share to below consensus to reflect this … we now forecast [ITV] third quarter [ad revenues] at -1.75% (+5% before)." How TV ad spend pans out in September will be key as it is always a solid indicator of the strength of the final three months of the year, when big ITV shows such as The X Factor return.
You can't hand down a conclusion based solely on this test, but it's a solid indicator of performance.
A solid indicator of Randy's primacy amongst lead-guitar-obsessives is a dazzling coffee-table book just released by Velocity Publishing simply titled, "Randy Rhoads".
By computing PR for a percentage of the papers accepted in a conference or journal, a more solid indicator of a venue's selectivity than the paper Acceptance Ratio (AR) can be derived.
Or is a first-class honours degree still a pretty solid indicator of professional potential?
A solid indicator, Days on Market (DOM) the average of 54 metro areas for homes sold in March 2018 was 60, down four days from March 2017.
"This 50-day high is a solid indicator that people are slowly re-entering the market," says Rob Viglione, co-founder of ZenCash.
But a somewhat more solid indicator of unread books emerged in 1985 when Michael Kinsley, then of The New Republic, acted on his suspicions about reading habits in the nation's capital.
