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If \({\bf{X}}\)has the \({\bf{p}}.{\bf{d}}.{\bf{f}}.\)\({\bf{1/}}{{\bf{x}}^{\bf{2}}}\)for\({\bf{x > 1}}\), the mean of \({\bf{X}}\) is infinite. What would you expect to happen if you simulated a large number of random variables with this \({\bf{p}}.{\bf{d}}.{\bf{f}}.\) and computed their average?

Short Answer

Expert verified

The mean would increase as number of observations increases.

Step by step solution

01

Definition for simulation

  • Simulation is model-based experimentation.
  • The model's behaviour imitates some salient aspect of the system under study's behaviour, and the user experiments with the model to infer this behaviour.
  • This broad framework has proven to be an effective tool for learning, problem solving, and design.
  • A probability density function (PDF) is a statistical expression that defines a probability distribution (the likelihood of an outcome) for a discrete random variable (for example, a stock or ETF) rather than a continuous random variable.
02

Determine the computation of average

  • Random variable\(X\)takes values which for large\(x\)get smaller.
  • By simulating large number,\(n\)of such variables, the average would get bigger as\(n\)increases.
  • This is because some values would be much larger then the others, which would appear more frequently when the number of observations increases. When the large observations appear, the mean increases.

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Most popular questions from this chapter

For each of the exercises in this section that requires a simulation, see if you can think of a way to use control variates or antithetic variates to reduce the variance of the simulation estimator.

Let \({\bf{Y}}\) be a random variable with some distribution. Suppose that you have available as many pseudo-random variables as you want with the same distribution as \({\bf{Y}}\). Describe a simulation method for estimating the skewness of the distribution of \({\bf{Y}}\). (See Definition 4.4.1.)

Let \(U\) have the uniform distribution on the interval\([0,1]\). Show that the random variable \(W\)defined in Eq. (12.4.6) has the p.d.f. \(h\)defined in Eq. (12.4.5).

Use the data in Exercise 16 of Sec. 10.7.

a. Use the nonparametric bootstrap to estimate the variance of the sample median.

b. How many bootstrap samples does it appear that you need to estimate the variance to within .005 with a probability of 0.95?

The \({\chi ^2}\) goodness-of-fit test (see Chapter 10) is based on an asymptotic approximation to the distribution of the test statistic. For small to medium samples, the asymptotic approximation might not be very good. Simulation can be used to assess how good the approximation is. Simulation can also be used to estimate the power function of a goodness-of-fit test. For this exercise, assume that we are performing the test that was done in Example 10.1.6. The idea illustrated in this exercise applies to all such problems.

a. Simulate \(v = 10,000\) samples of size \(n = 23\) from the normal distribution with a mean of 3.912 and variance of 0.25. For each sample, compute the \({\chi ^2}\) goodness of fit statistic Q using the same four intervals that were used in Example 10.1.6. Use the simulations to estimate the probability that Q is greater than or equal to the 0.9,0.95 and 0.99 quantiles of the \({\chi ^2}\) distribution with three degrees of freedom.

b. Suppose that we are interested in the power function of a \({\chi ^2}\) goodness-of-fit test when the actual distribution of the data is the normal distribution with a mean of 4.2 and variance of 0.8. Use simulation to estimate the power function of the level 0.1,0.05 and 0.01 tests at the alternative specified.

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