这个，并不矛盾，一个是短期的，一个是长期的；一个是从需求方面来讲的，一个是从供给方面来看的。

能讲清楚点吗

为了使问题简化，让我们假设劳动力是不增长的，所以分析个人收入相当于分析总收入。

其实短期中，由于价格具有粘滞性，所以无法用索洛模型这样的古典模型进行分析(其基本假设就是价格具有伸缩性)，而应该用凯恩斯的短期模型进行分析。根据凯恩斯交叉图.Y=C(Y-T)+I+G，这里T，I，G均作为外生变量给出，所以消费的增长无非就是Y增长或是T减少。在短期均衡状态中，Y增长(实际是背离均衡状态)引起消费增长后会引起存货的减少进而减少投资，最终回到均衡状态。T减少会以一个乘数带动国民收入的增长，达到较高的均衡状态。而索洛模型分析的是长期情况此时，此时Y只决定于K和L，因此其储蓄率越高达到的稳定状态的个人收入也越高的观点是合理的。

当储蓄率达到百分之一百时，引用柯布-道格拉斯函数作为生产函数，同样可以求得一个合理的k，但是没有一个政府会这样做。

 

[此贴子已经被作者于2007-11-29 21:34:39编辑过]

感觉还是没解释到要害呀

1# allen802

AN OVERLOOK AT AFFECTS ON SAVING AND INTEREST RATE THROUGH SUBSTITUTE AND INCOME EFFECTS IN TERMS OF INTERTEMPORAL CONSUMPTION
从跨期消费的替代效应和收入效应看利率、收入对储蓄的影响

One of the major macro policy concerns in China is the higher savings rate. Why is it the savings rate in China is higher than it is in most countries? In this section we will modify our model of choice to examine the decision to save.

Constraints
We begin with the assumptions that the individual earns income (I) today, he can spend his income either today (C1) or one year from today (C2), and any income not spent in the first period will earn r percent interest by the second period. Combining these constraints, we can specify the individual's budget constraint as:

C2 = (I-C1)*(1+r)

With a little reworking of the equation we can get the following linear equation:

C2 = I*(1+r) - C1*(1+r)

From your algebra you can recognize the first term in parentheses as the vertical intercept and the second as the slope. In the diagram below we can attain any of the points within the blue opportunity set and cannot attain anything outside given our existing constraints. At point at E all of the income is being spent in the second year while at F all of the income is being spent in the first year.

We can also look at the model to see how the opportunity set would change. Given the underlying equation, it is no surprise the curve would shift as a result of two possibilities: a change in the interest rate and a change in the level of income. In the left-side diagram we see the graphical representation of an increase in the interest rate. The Y axis of the budget constraint shifts upwards - if we save all of our income in the first period then we will have more to spend in the second period. If we spent all of our income in the first period, however, we would not be able to consume any more since the change in the interest rate would not alter today's income. In the right-side diagram we have the visual representation of an increase in income. The budget constraint shifts outward since both intercepts would now be larger.


Preferences
Now let's look at the other piece of the puzzle - the preferences. At this time we will keep it simple - we will assume the individual gets enjoyment, utility, from both consumption today and next year and the enjoyment increases as we consume more of each. We will also assume the individual can compare all commodity baskets. In the diagram below we can look at point A which represents a basket containing Y* of consumption next year and X* of consumption this year. Point B differs from point A in that the 'basket' contains more consumption today. Point C differs from B in that it has less consumption next year and differs from A in that it has less consumption next year and more consumption today. If we combine all of the commodity baskets that provide us with the same level of utility we obtain the negatively sloped curves U1 and U2, what we will call indifference curves. All of the 'baskets' represented by the line U1 contain points of indifference - you like them equally. The same is true for points on U2, except all points on B are preferred to those on U1 since we know B is preferred to both A and C.

On each indifference curve the slope is equal to the ratio of marginal utilities slope = MU1/MU2, where MU 2 is defined as the additional utility realized as we increase consumption of next year by one unit. If we were to show preferences changed, that our individual now valued consumption today more than before, MU1 would increase and this would increase the slope of the indifference curve.

The Complete Model
It is now time to combine the two pieces keeping in mind the goal is to explain the choice made by the individual attempting to maximize the level of satisfaction given preferences and constraints. If we combine the two graphs we get the diagram below which contains information on the constraints (opportunity set) and preferences (indifference curves U1...U4). What can we say about point B? It is within the budget constraint and on U1, which based on our earlier discussion, makes it clearly an inferior choice to A. Similarly C is obviously a superior choice to A, but it is not attainable. The result is A is the best we can do. Given our existing income and interest rates, this individual would choose Y* of consumption next period and X* of consumption today.

Note: There is a special property of the optimal choice - it is a tangency point between the budget constraint and the indifference curves. Given what we know of the two slopes we have the condition for optimal choice being: MU1/MU 2 = (1+r).

What can alter the choices of the individual? It should be clear from the graph above the choice was determined by the two curves which represented the budget constraint and the preferences. We will look briefly at each.

A decrease in the interest rate. We can see the increase in the interest rate shifts out the budget constraint. Using the same logic as before, we find A is no longer the 'best' choice and in fact now we have V being the optimal choice. The fact that V is directly above A means the individual is buying the same amount next period and this period. The change in consumption this period can be conceptually divided into two separate components - the income and substitution effects. As the price of a good changes, consumers will tend to substitute the cheaper for the more expensive - the substitution effect. As the interest rate increases the level of total income attainable increases which tends to increase consumption in both time periods - the income effect.

What we can see here is the income and substitution effects are often opposite of each other. As the interest rate increases, the substitution effect suggests a lower level consumption this period while the income effect suggests a higher level of consumption in both periods.

If we plotted the relationship between the level of savings and the interest rate we would get the individual's savings supply curve. If the substitution effect dominates, we would have the traditional positively sloped curve - as the interest rate increased individuals would increase their level of saving.

Derivation of Saving Supply Curve


An increase in Income. We can see tat the increase in income shifts out the budget constraint. Using the same logic as before, we find that neither A nor V are the 'best' choice and in fact now we have Z being the optimal choice. The fact that Z is up and to the right of A and V means the individual is consuming more in both periods as a result of a higher level of income.

Before leaving our discussion of intertemporal choice, let's examine a few of the factors that could influence the rate of time preference - the rate at which individual's discount the future.  One factor would be uncertainty about the future - as people became more uncertain about the future they would tend to discount the future more heavily and therefore it would not enter as much into their decisions today. In this case they would tend to save less which is consistent with the findings of an international study of savings rates.  Countries tended to have lower savings rates if their people believed there was a greater chance of nuclear war.  Economist Lowenstein, meanwhile, found evidence of a negative discount rate when a survey revealed people who had been told they won a kiss with their favorite movie star wanted to wait for a few days, while they wanted to receive a painful shock immediately.

retrieved from: http://www.uri.edu/artsci/newecn/Classes/Art/INT1/Mic/Utility/Out.Indchoice4.html