"direct indicator" is correct and usable in written English.
It is a term often used to refer to a signal or measure that provides information about a particular fact or situation. For example, "Sales figures are a direct indicator of customer demand."
Western blot analysis was used to visualize the phosphorylation of ERK1/2, a direct indicator of RAS pathway activation.
Diluted blood reperfusion as a model for transplantation of ischemic rat livers: alanine aminotransferase is a direct indicator of viability.
The precipitation is a direct indicator for the complexation between PAA and Ln ions.
Grassland desertification is the most direct indicator of the effect of the grazing ban.
Shipping is a direct indicator of whether people want goods, and softness in shipping prices is therefore a sign of weakness in manufacturing and construction.
Measuring a more direct indicator of neural activity, such as concentrations of neurotransmitters (brain chemicals that carry messages between neurons) could be much more valuable.
Benzyl succinic acid (BSA) was for the first time identified in a leachate plume as a direct indicator, and as the only intermediate of toluene degradation.
The engineering demand parameters were selected as the crest displacement, the maximum crest acceleration and the crack extent, a direct indicator of the damage on the monoliths.
For neighbourhood search methods, one direct indicator of problem difficulty is the number of local optima that exist in the problem landscape.
Bypassing volumes provide a direct indicator of annual longshore sediment transport rate over this most recent cycle of 30 40 × 103 m3 yr− 1.
Cryostructure or the pattern of ice inclusions within a frozen soil is a direct indicator of the geologic and cryogenic genesis of permafrost soils.
