For a compound, you have accurate G data for all values of P that are in the range 1 – 5 MPa, and also in the range P = 7 – 13 MPa. A model exists, but it only agrees with the data below 10 MPa, and not at all above 10 MPa. You need to make a continuous plot for G that covers the entire range from 2 to 15 MPa. Which of the following is most reasonable course of action?

Question

A. Extrapolate from the 1 – 5 MPa data range up to 15 MPa.
B. Interpolate between the 1 – 5 MPa data range and 7 – 13 MPa data range.
C. Interpolate between the 1 – 5 MPa data range and 7 – 13 MPa data range and then extrapolate the data up to 15 MPa.
D. Use the data from 1 to 5 MPa, then the model from 5 to 7, then the data from 7 to 13 MPa. Finally extrapolate the data up to 15 MPa.
E. Use the data from 1 to 5 MPa, then the model from 5 to 7, then the data from 7 to 13 MPa. Finally, model the data up to 15 MPa.

Answer 1

A. Incorrect. We have data and models for the 6 to 13 MPa range which should be used instead of extrapolation, which is fraught with risks.
B. Incorrect. This does not complete the requirements.
C. Incorrect. Simple interpolation, while more accurate than extrapolation, is not as accurate as a validated model used within its appropriate range of conditions.
D. Correct. If good data is available it should be used in preference to everything else. Models are appropriate where they closely follow the data and extrapolation is a last resort if nothing else is available, which is the case from 13-15 MPa.
E. Incorrect. The model is stated as totally unreliable at this pressure, so using it is worse than having no data.