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7. The Sampling Distribution

7.3.1 The Law of Large Numbers

  • The Law of Large Numbers states that, as the sample size becomes larger, the sampling distribution of the sample average becomes more and more concentrated about the expectation.
  • the variances decrease with the increase of the sample sizes. The decrease is according to the formula Var( ¯X ) = Var(X)/n.
  • The variance is a measure of the spread of the distribution about the expectation. The smaller the variance the more concentrated is the distribution around the expectation. Consequently, in agreement with the Law of Large Numbers, the larger the sample size the more concentrated is the sampling distribution of the sample average about the expectation.

7.3.2 The Central Limit Theorem (CLT)

  • The Law of Large Numbers states that the distribution of the sample average tends to be more concentrated as the sample size increases. The Central Limit Theorem (CLT in short) provides an approximation of this distribution.