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Mathematics · unit version 1

Mathematical statistics: derivation and model criticism

Twenty-two lessons deriving estimators, tests, intervals and regression from probability models. Exact finite-sample results, regular asymptotic approximations and model-dependent decisions are distinguished. Mixed assessment, independent analysis and proof review remain separate requirements; topic coverage alone does not establish semester equivalence.

Open any lesson. Completion records participation; automatic practice checks and human judgment of written arguments are separate. This unit retains its own versioned requirements.

Readiness and preparation

Check your starting point

Try these short questions on paper, then compare your reasoning. They are optional self-checks, not a placement score or a navigation requirement. Use a targeted review when useful and return with your browser’s Back control.

For independent Bernoulli(p) observations, what are the expectation and variance of their sample mean?

Estimator risk begins with a sampling distribution under stated assumptions.

Compare reasoning and find a refresher

The expectation is p and the variance is p(1−p)/n. Independence removes covariance terms; identical success probabilities make the common parameter p meaningful.

Review expectations and covariance of sums

What is random in a frequentist confidence procedure?

Parameter, statistic and random interval have different roles in mathematical inference.

Compare reasoning and find a refresher

The data and resulting interval vary under repeated sampling; the target parameter is fixed. Coverage is a property of the procedure under a specified model, not a probability assigned to that fixed parameter after observing one interval.

Review confidence and coverage

Why does conditioning a square-integrable random variable reduce its mean squared prediction error?

Conditional expectation underlies Rao–Blackwell improvement and several statistical decompositions.

Compare reasoning and find a refresher

The conditional mean is the orthogonal squared-error predictor among functions of the conditioning information. Expanding the square yields an irreducible conditional-variance term plus the squared difference from that mean.

Review conditional prediction and total variance

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Mathematical statistics: derivation, decisions and model checks

The mixed assessment has separate response history and review criteria; it does not change lesson participation records.

Statistical investigation: vehicle efficiency, model revision and changed targets

Sustained investigation with separate transfer evidence, saved revisions and human review. It does not change lesson participation requirements.

Lesson sequence

Each linked lesson opens on its own page. Expand its details here when you want to check the objectives before choosing.

  1. Specify the experiment before estimating

    Lesson details and objectives

    Separate the sample space, parameter, statistic and sampling design.

    • Write a dominated statistical model.
    • Distinguish parameter from statistic.
    • Explain how design changes the joint law.

    6 practice tasks.

  2. Compare parameter values for fixed data

    Lesson details and objectives

    Use likelihood ratios and distinguish observationally equivalent parameters.

    • Compute likelihood ratios.
    • Prove or refute identifiability.
    • Distinguish likelihood from a posterior law.

    6 practice tasks.

  3. Compare estimators through expected loss

    Lesson details and objectives

    Derive MSE and distinguish pointwise risk from universal preference.

    • Prove the bias–variance decomposition.
    • Compute risks under squared loss.
    • Explain why unbiasedness is not optimality.

    6 practice tasks.

  4. Connect sample moments to population parameters

    Lesson details and objectives

    Use convergence arguments and identify weak points in moment matching.

    • Prove consistency using LLN.
    • Apply continuous mapping correctly.
    • Distinguish consistency from unbiasedness.

    6 practice tasks.

  5. Optimize the whole parameter space

    Lesson details and objectives

    Handle support constraints, boundary maxima and nonexistence.

    • Derive MLEs with support indicators.
    • Check stationary points against boundaries.
    • Use invariance without assuming unbiasedness.

    6 practice tasks.

  6. Compress data without losing model information

    Lesson details and objectives

    Use conditional distributions and dominated factorization.

    • State sufficiency in conditional-law terms.
    • Apply the factorization theorem.
    • Explain model dependence of sufficiency.

    6 practice tasks.

  7. Recognize a common likelihood architecture

    Lesson details and objectives

    Derive moments from the log normalizer and respect the natural parameter space.

    • Identify canonical statistics and natural parameters.
    • Differentiate the log partition under stated conditions.
    • Distinguish full from curved families.

    6 practice tasks.

  8. Improve an estimator by conditioning

    Lesson details and objectives

    Derive risk reduction and show where sufficiency enters.

    • Prove conditional-expectation variance reduction.
    • Keep the improved statistic parameter-free.
    • Characterize squared-loss equality.

    6 practice tasks.

  9. Turn unbiasedness into uniqueness

    Lesson details and objectives

    Prove a complete-family example and the Lehmann–Scheffé conclusion.

    • Define completeness with integrability.
    • Prove binomial completeness.
    • Derive UMVU optimality among unbiased estimators.

    6 practice tasks.

  10. Measure local likelihood sensitivity

    Lesson details and objectives

    Derive an information bound and inspect regularity failures.

    • Compute score and information.
    • Prove the scalar Cramér–Rao inequality.
    • Identify support and boundary failures.

    6 practice tasks.

  11. Derive the regular large-sample approximation

    Lesson details and objectives

    Use score expansion and distinguish a theorem from a diagnostic.

    • Explain the score Taylor expansion.
    • State essential asymptotic regularity.
    • Diagnose boundary and unidentified cases.

    6 practice tasks.

  12. Propagate asymptotic uncertainty through a transformation

    Lesson details and objectives

    Use first- and second-order expansions where appropriate.

    • Derive the scalar delta method.
    • Compute transformed variance s.
    • Diagnose a zero derivative.

    6 practice tasks.

  13. Derive exact normal-model inference

    Lesson details and objectives

    Use orthogonal decomposition to prove t and chi-square pivots.

    • Derive independence of mean and residual variation.
    • Construct t and chi-square pivots.
    • Distinguish exact normality from approximation.

    6 practice tasks.

  14. Optimize a test against a specified alternative

    Lesson details and objectives

    Prove the likelihood-ratio ordering and handle randomization.

    • Define test size and power.
    • Prove the Neyman–Pearson lemma.
    • Randomize at a discrete boundary when required.

    6 practice tasks.

  15. Build one test for a one-sided family

    Lesson details and objectives

    Use monotone ratios and stochastic ordering to control a composite null.

    • Verify an MLR ordering.
    • Prove one-sided size control.
    • Explain the limits of UMP claims.

    6 practice tasks.

  16. Compare constrained and unconstrained fits

    Lesson details and objectives

    Derive a likelihood-ratio statistic and mark the limits of Wilks calibration.

    • Compute a constrained likelihood ratio.
    • Explain regular chi-square asymptotics.
    • Identify boundary and nuisance failures.

    6 practice tasks.

  17. Invert tests into coverage statements

    Lesson details and objectives

    Connect acceptance sets, confidence sets and prospective power.

    • Prove test–confidence duality.
    • Distinguish pointwise coverage from conditional probability.
    • Analyze power under a specified effect.

    6 practice tasks.

  18. Choose an action by posterior expected loss

    Lesson details and objectives

    Derive conjugate updating and separate prior-sensitive decisions from sampling guarantees.

    • Derive a beta–binomial posterior.
    • Choose Bayes actions under specified loss.
    • Distinguish credible and confidence sets.

    6 practice tasks.

  19. Use geometry to derive sampling laws

    Lesson details and objectives

    Whiten normal vectors and identify independent orthogonal quadratic forms.

    • Derive normal projection independence.
    • Compute chi-square rank s.
    • Explain why uncorrelated normal blocks are independent.

    6 practice tasks.

  20. Derive regression inference from projections

    Lesson details and objectives

    Separate fixed-design algebra from normal-error inference.

    • Derive least squares and coefficient covariance.
    • Prove residual chi-square and F laws.
    • State nested-model assumptions.

    6 practice tasks.

  21. Find the assumptions that drive a reported standard error

    Lesson details and objectives

    Use leverage and residual covariance to diagnose model departures.

    • Derive residual variance s and leverage constraints.
    • Explain heteroskedastic covariance.
    • Distinguish diagnostic evidence from assumption proof.

    6 practice tasks.

  22. Approximate a sampling law without forgetting its model

    Lesson details and objectives

    Derive empirical resampling and diagnose nonsmooth or dependent failures.

    • Compute a bootstrap distribution in a finite case.
    • State when permutation calibration is exact.
    • Explain failures for extrema and dependent samples.

    6 practice tasks.