How Economist predict Price Using the Theory of Supply and Demand?

First trader should look for supply and Demand to predict the price

In Currency Supply is considered from Economic Indicators M0 & M1 Money supply rising or droping. 

    Currency Demand when Central banks comments to hike interest rates or rising inflation etc. 

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In Commodities ,

     Gold supply is considered production from various gold mines,silver mines etc

     Gold Demand when economy of large gold consumers rises like china economy. 

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     Crude oil supply is considered production from largetest oil producers.

     Crude oil demand ,when economy starts to rise of  major countries.