1. Problem Definition
Indonesia is still importing 75% of the domestic soybean demand of 2.5 million tons. The high dependence on imported soybeans make the government was powerless when soybean prices rose due to the weakening of the rupiah against the U.S. dollar (U.S.). As we know that soybean is the basic ingredients for tofu and tempe which are the most popular food here. Now I try to made 6 months future cost estimation of imported soybean price and use a new alternative currency reference with gold that consider as stable currency.
2. Development of Feasible Alternatives
The predicted price will estimate by trendline from soybean price in oz gold value and by analyze SPC (Statistical Process Control).
3. Development Outcomes for Alternative
Below are the historical data of the average price of gold, exchange rate and soybean per month from Jan 2012 to Oct 2013:
Here is a picture that shows the graph of data above.
4. Selection of Criteria
Convert the soybean price (Rp/gram) into gold equivalent (oz or troy-ounce), so that soybean price will refer to gold price. The historical data and its 6 months trendline of monthly average price of soybean in gold equivalent (gram soybean/oz Gold) from Jan 2012 to October 2013 (actual data) is presented in below.
From 6 trendline model which close to describe the forecast, below are the R-squared :
5. Analysis of the Alternatives
Using observed data from January 2012 to Oct 2013 (22 data) the equation for forecasting Soybean value in gold equivalent is displayed below, in which y is Soybean Equivalent and x is monthly time unit 22 + n. Selection to the 4th order polynomial models based on the most moderate value among other models and also has quite large value of R-squared (0.8868).
y = 0.0587x4 – 2.7655x3 + 40.216x2 – 195.4x + 1750.8
Now, the SPC analysis show the result below :
So thus obtained control chart graph as below :
From control chart above, we can say that the data are out of control since the data are match one of the “out of control” criteria . To make adjusted control chart, some data have to be taken out.
6. Selection of Preferred Alternative
But in this blog, the control chart is better in term of data matching and more comfortable to be used in forecast purpose since it allows plus/minus sigma as a value range . Therefore, the value of soybean for 6 months onward will be between 1214.65 and 1712.54 Gram / gold oz.
7. Performance Monitoring & Post Evaluation of Results
At this time, the value of the Rupiah continues to fall against the USD to make soybean import prices go up. If the price of imported soybean based on the price of gold, the price of soybeans will be relatively more stable. Control chart analysis could be made better by predict the price range in the coming months with daily data.
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