This is the sixth of six segments that show you how to improve the ozone prediction surface.

You can create a prediction standard error surface to examine the quality of the predictions.

Click the layer name to select it, then click it again and change it to "Trend Removed". Right-click the Trend Removed layer that you created and click Create Prediction Standard Error Map.

The prediction standard errors quantify the uncertainty for each location in the surface that you created. A simple rule of thumb is that 95 percent of the time, the true value of the surface will be within the interval formed by the predicted value, plus or minus 2 times the prediction standard error if data is normally distributed. Notice in the prediction standard error surface that locations near sample points generally have lower error.

The surface you created in Exercise 1 simply used the defaults of Geostatistical Analyst, with no consideration of trends in the surface, of using smaller lag sizes, or of using an anisotropic semivariogram model. The prediction surface you created in this exercise took into consideration the global trends in the data, adjusted the lag size, and adjusted for the local directional influence (anisotropy) in the semivariogram.