Fundamentals of Surveying (FS) Practice Exam

When calculating vertical accuracy using NSSDA, the RMSE is multiplied by what value?

1. 1.5

2. 1.75

3. 1.96

4. 2.0

The correct answer is: 1.96

The value that the RMSE (Root Mean Square Error) is multiplied by when calculating vertical accuracy using the National Standard for Spatial Data Accuracy (NSSDA) is based on the desired confidence level in the data. The coefficient of 1.96 corresponds to a 95% confidence level in a normal distribution. This means that if you have a normally distributed set of errors, approximately 95% of the errors will fall within 1.96 standard deviations from the mean. By multiplying the RMSE by this factor, you are providing a more meaningful representation of the accuracy by illustrating that most of the points can be expected to fall within this range. This method is often used in statistical analyses to establish confidence intervals and enable users to gauge the reliability of the measurements. Using any other multiplier would indicate a different confidence level, which may not align with the standard practices for reporting vertical accuracy according to NSSDA. Hence, 1.96 is the appropriate constant to use in this context.