Math 2.0

Statistics Definition

Confidence interval

Builds on StatisticNormal distributionSample meanStandard score

Definition

Let XX be a sample whose law PθP_\theta depends on an unknown parameter θ∈Θ\theta \in \Theta. Let τ ⁣:Θ→ℝ\tau \colon \Theta \to \mathbb{R} be a function and let γ∈(0,1)\gamma \in (0, 1). A confidence interval for τ(θ)\tau(\theta) with confidence level γ\gamma is a random interval [L(X),U(X)][L(X), U(X)], where L≤UL \le U are statistics, such that Pθ(L(X)≤τ(θ)≤U(X))=γfor each θ∈Θ.P_\theta\big(L(X) \le \tau(\theta) \le U(X)\big) = \gamma \quad \text{for each } \theta \in \Theta. If only "≥γ\ge \gamma" holds for each θ\theta, the interval is a conservative confidence interval.

Remarks

Example: let X1,…,XnX_1, \dots, X_n be i.i.d. 𝒩(μ,σ2)\mathcal{N}(\mu, \sigma^2) with σ\sigma known. Then Xˉn±1.96 σ/n\bar{X}_n \pm 1.96\, \sigma / \sqrt{n} is a confidence interval for μ\mu with level approximately 0.950.95. If σ\sigma is unknown, one replaces σ\sigma with the sample standard deviation and 1.961.96 with a quantile of Student's t-distribution with n−1n - 1 degrees of freedom. The probability refers to the random interval, not to θ\theta. After one computes the interval from data, it either contains τ(θ)\tau(\theta) or it does not. The confidence level is often written as 1−α1 - \alpha, for example 95%95\% for α=0.05\alpha = 0.05.

Reading path

To understand this page from the ground up, read these 73 pages in order. The foundations come first.

  1. Construction of the reals from Cauchy sequences concept
  2. Element definition
  3. Integers object
  4. Ordered field definition
  5. Proposition concept
  6. Random experiment concept
  7. Rational numbers object
  8. Real numbers object
  9. Set definition
  10. Ring of integers statement
  11. Disjunction definition
  12. Implication definition
  13. Predicate definition
  14. Ordered pair definition
  15. Union definition
  16. Sample space definition
  17. The rationals form a field statement
  18. Existential quantifier definition
  19. Universal quantifier definition
  20. Cartesian product definition
  21. Subset definition
  22. The rationals form an ordered field statement
  23. Uniqueness quantifier definition
  24. Binary relation definition
  25. Universal set definition
  26. Order on the reals definition
  27. Power set definition
  28. Complement definition
  29. Function definition
  30. Interval definition
  31. Indicator function definition
  32. Injective function definition
  33. Preimage of a set definition
  34. Sigma-algebra definition
  35. Countable set definition
  36. Event definition
  37. Borel sigma-algebra definition
  38. Probability axioms concept
  39. Probability measure definition
  40. Dirac measure definition
  41. Probability distribution definition
  42. Probability space definition
  43. Conditional probability definition
  44. Random variable definition
  45. Discrete random variable definition
  46. Cumulative distribution function definition
  47. Independence of two events definition
  48. Law of a random variable definition
  49. Standard score definition
  50. Random variable with a density definition
  51. Joint probability distribution definition
  52. Independence of two random variables definition
  53. Mutual independence of events definition
  54. Expected value definition
  55. Identically distributed random variables definition
  56. Probability density function definition
  57. Marginal distribution definition
  58. Variance definition
  59. Independent sigma-algebras definition
  60. Linearity of expectation statement
  61. Density of the normal distribution definition
  62. Independence means the joint law is the product of the marginals statement
  63. Independence of random variables definition
  64. Covariance definition
  65. Normal distribution definition
  66. Expectation of a product of independent random variables statement
  67. Variance of a sum statement
  68. Independent and identically distributed random variables definition
  69. Independent random variables are uncorrelated statement
  70. Statistic definition
  71. Variance of a sum of independent random variables statement
  72. Sample mean definition
  73. Confidence interval definition

Where this leads

4 pages build on this one.

Further reading

  1. Web https://en.wikipedia.org/wiki/Confidence_interval, Definition
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URIm2://0K4NMMJBG2
Kinddefinition
WritingW1 stated
MSC62F25
DefinesConfidence interval
UsesStatistic, Normal distribution, Sample mean, Standard score

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