请问c选项是哪种方法的weakness？

问题如下：

Susan Clark is a research analyst with Billingham Associates, an international investment advisory firm. Clark is responsible for informing the investment committee of current events in foreign economies. The investment committee relies on the information Clark provides to help in their asset allocation decisions. Clark obtains a considerable amount of information through her contacts with colleagues around the world.

The investment committee is seeking new ways to project economic scenarios and assess their effects on local stock markets. Clark explains to the investment committee that there are three major methods of economic forecasting:

Ÿ econometric models, which are the most formal and mathematical of the three,

Ÿ indicators, which are variables that may lead, lag or be concurrent with shifts in the economy, and

Ÿ the checklist approach, in which an analyst considers an array of economic data.

The investment committee informs Clark that its members are interested in increasing allocations to bonds and real estate in a number of client investment portfolios. However, there is also a concern regarding forecasts of rising global inflation and the effects of this inflation on bond and real estate asset classes. Clark has been asked to analyze these effects.

Billingham is considering investments in four countries that are new to its investment portfolio. The investment committee asks Clark to provide research on the following countries:

Country A

Clark has learned that Country A has a government program that uses grants, subsidies and tax incentives to encourage competition and to nurture new product development. However, some politicians in Country A are reluctant to endorse the program and would like the grants, subsidies and incentives to be reduced or eliminated. The investment committee wants to know what effect a cancellation of the program may have on Country A’s economy.

Clark’s knows that there are three types possible outcomes if the government program is reduced or eliminated:

Type 1: A persistent (permanent, one-time) decline in the level of output, but the subsequent trend rate of growth is unchanged.

Type 2: No persistent decline in the level of output, but the subsequent trend rate of growth is reduced.

Type 3: Both a persistent decline in the level of output and a reduction in the subsequent trend rate of growth.

Country B

The investment committee is considering increasing exposure to Country B’s equity market. Clark’s analysis of Country B’s economy shows that the country’s central bank is pursuing an independent monetary policy and is allowing unrestricted capital flows. She also knows that despite the country maintaining a floating exchange rate, there is increasing pressure to establish a fixed exchange rate.

Country C

The investment committee is considering investing in fixed income instruments issued by companies domiciled in Country C and denominated in Country C’s currency. Bill Johnson, a member of Clark’s research group, has been asked by Clark to analyze interest rates in Country C. Johnson’s report indicates that the consensus opinion within the country is that, in the near term, interest rates are expected to rise.

Country D

Country D is categorized as an emerging market. The investment committee has little experience in emerging market investments and has asked Clark for more information. Ralph Norwood, another member of Clark’s research team, studied Country D’s economy and compiled the economic ratios listed in Exhibit 1.

A limitation of the econometric model approach for forecasting that Clark might conclude is:

选项：

A.Past forecast errors can be ignored as an additional explanatory variable into the model.

B.Econometric models require the user to find adequate measures (which may be unavailable) for the real-world activities and relationships to be modeled.

C.Relationships among the variables rarely, if ever, change over time because of changes in economic structure and/or because the model may have been based on faulty assumptions as to how the economy works.

解释：

Econometric models require the user to find adequate measures (which may be unavailable) for the real-world activities and relationships to be modeled.

Answer Choice (A) is incorrect. Past forecast errors are incorporated into the model as an additional explanatory variable. Answer Choice (C) is also incorrect. Relationships among the variables may change over time because of changes in economic structure and/or because the model may have been based on faulty assumptions as to how the economy works.