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A Level · Cambridge (CIE) · 9709

Calculate normal test errors and compare sample-size power

Translate the fixed mean decision region under a specified alternative and compare its sensitivity.

Statistics 2 · Hypothesis tests · 6.5
Exam scope and assessment notes

Probability & Statistics 2 (Paper 6, A Level) · Mathematics 9709, 2026–2027, section 6.5. Paper 6 builds on Paper 5 and assumes Paper 3 calculus. Specify population hypotheses, significance level, test statistic and tail direction before inspecting the result. Calculate tail probabilities under H₀, including the observed discrete value. A p-value is not the probability that H₀ is true. Reject H₀ when the specified tail probability is at most the stated significance threshold; otherwise do not reject. The syllabus term acceptance region means the non-rejection region, not proof of H₀. For two-sided discrete examples here, use an explicitly stated equal-tail allocation; asymmetric discrete models admit different conventions, so do not treat twice the smaller tail as a universal definition. Integer critical regions can have actual Type I probability below the nominal level. Normal approximations need a suitable model and continuity correction for counts; check exact probabilities when approximation could change a close decision. Mean tests use a normal population with known variance or an adequate large independent sample with estimated variance. Small samples with unknown variance do not automatically justify the z method. Type I means rejecting a true null; Type II means not rejecting a false null at a specified alternative. Calculate error probabilities using the fixed decision region under the relevant parameter, not by changing the test after seeing data. Power is one minus Type II probability at that alternative. Quoted normal critical values and table probabilities have rounding limits. Interpret evidence in context without claiming certainty, causation or practical importance. Written practice is self-checked; cumulative assessment and human subject-teacher review remain pending.

Before you begin

  • Use the normal distribution of a sample mean.
  • Standardise using the relevant true mean.

Work on paper. Try each question before revealing help, and explain why your method works.

Quick readiness check

What mean is used to standardise β at true μ = 104?

What you will learn

  • Calculate normal Type I and Type II areas.
  • Compare power while holding level and effect fixed.
Null sample-mean density N(100,4) in blue and specified alternative density N(104,4) in green share a partial 94–110 axis and SE two. The original upper critical boundary remains 103.29. Null probability to its right is Type I; alternative probability to its left is Type II, approximately 0.3612948. Curves omit tails outside the drawing and no shaded-area geometry is asserted.One boundary · two true distributions100104Fixed boundary 103.29Blue null: right tail is Type IGreen alternative: left tail is Type IIβ ≈ 0.3612948 · power ≈ 0.6387052Partial curves · same SE two
Null sample-mean density N(100,4) in blue and specified alternative density N(104,4) in green share a partial 94–110 axis and SE two. The original upper critical boundary remains 103.29. Null probability to its right is Type I; alternative probability to its left is Type II, approximately 0.3612948. Curves omit tails outside the drawing and no shaded-area geometry is asserted.

Fix the mean boundary under the null

For a normal population with known σ = 12, n = 36 gives SE two. The upper 5% test of μ = 100 uses quoted z = 1.645 and rejects when X̄ > 103.29. Under μ = 100 its actual continuous-tail probability is approximately 0.0499849, reflecting critical-value rounding.

At true μ = 104, not rejecting means X̄ ≤ 103.29. Standardise under that true mean: z = (103.29 − 104)/2 = −0.355. Thus β ≈ 0.3612948 and power ≈ 0.6387052. Keep the boundary 103.29 rather than moving it to 107.29.

More independent data can improve this test

With n = 144, SE is one. Keeping the same one-sided 5% level and alternative μ = 104, the new designed null boundary is 101.645. At the alternative, β = Φ(−2.355) ≈ 0.00926135 and power ≈ 0.99073865. This comparison assumes the same normal model and independent observations.

For the n = 36 two-sided 5% test, the non-rejection interval is [96.08,103.92]. At μ = 104, β = Φ(−0.04) − Φ(−3.96) ≈ 0.4840091. Both limits must be used. These calculated powers are specific to the stated models and alternatives, not general guarantees of learner or experimental success.

Pause and explain

What is the two-sided non-rejection event for the n = 36 rule?

Put the idea to work

Worked example

Find β at μ = 104 for the fixed upper boundary 103.29 and SE two.

Show the worked solution
  1. The non-rejection event is X̄ ≤ 103.29.
  2. Under μ = 104, z = −0.355.
  3. β ≈ 0.3612948; power ≈ 0.6387052.

Answer β ≈ 0.3612948.

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From guided practice to a new situation

Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.

1 · Guided

For rejection X̄ > 103.29, SE two and true μ = 104, find β and power.

Give me a hint

Standardise the fixed non-rejection boundary under mean 104.

Compare my reasoning
  1. Non-rejection is X̄ ≤ 103.29.
  2. z = −0.355; β ≈ 0.3612948.
  3. Power ≈ 0.6387052.

β 0.3612948; power 0.6387052.

Look for these in your work

  • Keep the boundary fixed.
  • Use the alternative mean.
2 · Independent

With n = 144, σ = 12 and the same upper 5% test, calculate β at μ = 104.

Give me a hint

First design the null boundary with SE one, then use the alternative model.

Compare my reasoning
  1. SE = 1; boundary = 100 + 1.645 = 101.645.
  2. At μ = 104, z = −2.355.
  3. β ≈ 0.00926135; power ≈ 0.99073865.

β 0.00926135; power 0.99073865.

Look for these in your work

  • Hold the level fixed.
  • Distinguish redesign from evaluating a fixed rule.
3 · Transfer

For n = 36 and two-sided rejection outside [96.08,103.92], calculate β at μ = 104.

Give me a hint

Use the central non-rejection interval under N(104,4).

Compare my reasoning
  1. Lower z = −3.96; upper z = −0.04.
  2. β = Φ(−0.04) − Φ(−3.96) ≈ 0.4840091.
  3. Power ≈ 0.5159909.

β 0.4840091; power 0.5159909.

Look for these in your work

  • Use both limits.
  • Retain the original null-centred region.

Common mistakes

  • The original boundary stays fixed for β.
  • Use the alternative mean when standardising β.
  • Two-sided β uses both non-rejection limits.
Recall without your notes

What can you explain now?

For β, should the upper boundary move with the alternative mean?

Compare with the explanation

No.

That would change the tested procedure instead of evaluating its sensitivity.

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Make it stick

Keep a test’s region fixed, change to the specified true distribution, and integrate the appropriate error event.

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Course scope and assessment

312 sequenced lessons provide 936 guided, independent and application problems covering the 160 objectives in sections 1.1–1.8, 2.1–2.6, 3.1–3.9, 4.1–4.5, 5.1–5.5 and 6.1–6.5. The map lists all 38 sections across six alternative components; all eight Pure Mathematics 1 sections and all six Pure Mathematics 2 sections, from Paper 2 Algebra through Numerical solution of equations, currently have full teaching sequences. Paper 3 Algebra, section 3.1, links the six shared foundation lessons plus six lessons on partial fractions and rational binomial expansions; Paper 3 logarithms, trigonometry and numerical equations use the shared lessons, with the Paper 1 graph foundation linked into trigonometry. Paper 3 differentiation combines the shared methods with its inverse-tangent derivative lesson. Paper 3 Integration links four shared standard and identity lessons plus seven advanced lessons, covering all six section 3.5 requirements. Eight Vectors lessons cover all six section 3.7 requirements, with 2D and 3D line and solid applications. Nine Differential equations lessons cover all four section 3.8 requirements, including Paper 3 integration techniques, initial conditions, equilibrium solutions and conditional model interpretations. Eleven Complex numbers lessons cover all eight section 3.9 requirements, with seven Argand diagrams and explicit argument and boundary checks. All nine Pure Mathematics 3 sections now have teaching linked to every mapped requirement. Nine Forces and equilibrium lessons cover all seven section 4.1 requirements, with six force diagrams, signed incline-friction intervals, reaction-dependent pull and push limits and separate-body third-law checks. Nine Kinematics lessons cover the four official section 4.2 requirements, with the graph requirement mapped to three relationships. Six motion diagrams support directed quantities, graph slopes and signed areas, Paper 1 time-calculus methods, reversal distances, constant-acceleration stages and shared-clock particle meetings. Six Momentum lessons cover both section 4.3 requirements, including signed system totals, conservation assumptions, outgoing velocities, coalescence, unknown masses and successive impacts. Four diagrams show system momentum through the stipulated events, and supplied kinetic-energy checks distinguish conservation of momentum from changes in kinetic energy. Twelve Newton’s laws lessons cover all four section 4.4 requirements, with vertical support and release stages, rough horizontal and incline motion, inferred parameters, hanging and surface pulley systems, rigid tow-bar thrust and slack-string transitions. Seven force diagrams support the separate-particle balances. Nine Energy, work and power lessons cover all five section 4.5 requirements, with angle-dependent work, kinetic and reference potential energy, signed net-work balances, smooth curved slides, rough and driven slopes, ideal connected-system energy and instantaneous power on hills. Five diagrams distinguish the energy inputs, losses and valid positive-speed force model. All five Mechanics sections now have teaching and staged practice linked to their mapped requirements. Thirteen Representation of data lessons cover all five section 5.1 requirements, including choice and limitations of displays, ordered and back-to-back stems, raw summaries and box plots, unequal-width density histograms, cumulative-frequency interpolation, descriptive moment calculations, grouped estimates, coding, combining two datasets and correcting totals. Six accessible diagrams retain repeated observations and distinguish numerical spread, frequency area and estimated readings. Ten Permutations and combinations lessons cover both official section 5.2 requirements, with selection and ordered roles, repeated objects, adjacency blocks, non-adjacency gaps, leading-zero cases, labelled multi-row seating and mixed restrictions. Six accessible diagrams show outcome trees, ordered versus unordered choices, repeated copies, blocks, gaps and distinct row seats. Eleven Probability lessons cover all four section 5.3 requirements, with equiprobable elementary outcomes, selection-based probabilities, complements and disjoint regions, independence tests, restricted sample spaces, two-way tables, replacement and removal trees, reversed conditions and unknown parameters. Seven accessible diagrams show dice outcomes, random subsets, event regions, a conditioned grid, a count table and two probability trees. Twelve Discrete random variables lessons cover all three official section 5.4 requirements, with complete probability tables, moment and parameter checks, binomial assumptions, exact probabilities and moments, geometric first-success probabilities, tails, expectation and integer reliability thresholds. Six accessible diagrams distinguish outcome grouping, weighted moments, fixed trials, discrete probability bars, waiting conventions and integer tail deadlines. Twelve Normal distribution lessons cover all three official section 5.5 requirements, with continuous-area interpretation, MF19 cumulative tables, full standardisation, tail and interval regions, conditional probabilities, percentiles, one- and two-parameter inference, binomial suitability, continuity corrections and approximate integer thresholds. Seven accessible diagrams show model areas, table reading, aligned scales, intervals, quantiles, matched binomial and normal shapes and whole integer cells. All five Statistics 1 sections now have teaching and staged practice linked to their mapped requirements. Fourteen Poisson distribution lessons cover all five official section 6.1 requirements, with homogeneous event-count assumptions, exposure scaling, exact masses and tails, conditional count events, moments, parameter inference, probability duration targets, disjoint and overlapping windows, rare-count binomial approximations, matched normal approximations and continuity corrections. Nine accessible diagrams show event exposures, unit conversions, discrete bars, complete tail complements, population moments, shared windows, approximate count models and integer cells. Exact checks distinguish approximate and exact close-target decisions. Fourteen Linear combinations lessons cover the six listed results in official section 6.2, with affine moments, signed scales and constant cases, expectation without independence, independent squared variance contributions, fixed and random fees, independent copies versus reused values, affine normal events, independent normal sums and differences, weighted and conditional areas, coefficient inference, exact independent Poisson sums and overlapping exposure limits. Nine accessible diagrams distinguish scale changes, variance contributions, component costs, copy mechanisms, aligned normal scales, summed areas, Poisson count pairs and unsupported distribution claims. Fourteen Continuous random variables lessons cover both official section 6.3 requirements, with density validity and units, support-aware intervals, complements and conditional regions, first and second moments, percentiles by direct density areas, symmetry checks, parameter inference, infinite-support power and exponential integrals, divergent-moment limits and combined applications. Nine accessible diagrams distinguish density height from probability, normalisation, negative-density failures, central and conditional areas, mean versus median, percentile locations and partial infinite tails. Explicit cumulative distribution function knowledge is not required. Eighteen Sampling and estimation lessons cover all eight official section 6.4 requirements, with population and frame definitions, random-number selection, sampling-quality limits, independent sample-mean moments, normal means, CLT conditions, SE scaling, raw, summarised and coded unbiased estimates, known-variance and large-sample mean intervals, repeated-sampling interpretation, precision planning, proportion intervals, sparse-outcome limits and contextual applications. Ten accessible diagrams distinguish selection frames, number rejection, repeated sample means, population versus mean density, CLT models, variance divisors, interval targets, illustrative coverage, integer size checks and proportion margins. Eighteen Hypothesis tests lessons cover all five official section 6.5 requirements, with pre-specified alternatives, inclusive count tails, explicit equal-tail conventions, integer critical regions and actual significance, exposure-aware Poisson tests, continuity-corrected count approximations, normal and large-sample mean tests, confidence-interval connections, error classifications, fixed-region binomial, Poisson and normal error probabilities and sample-size power comparisons. Nine accessible diagrams show the testing procedure, exact count regions, unequal Poisson tails, discrete significance jumps, corrected count boundaries, matching mean intervals and alternative error distributions. All shared lessons are counted once in the course total. All 38 sections now link teaching and practice. Eight earlier overview lessons remain available, but do not count as full section coverage. This is a content-availability measure, not full programme completion or exam readiness. Written practice is self-checked, not officially marked. Check the 2028–2030 syllabus separately if sitting an examination from 2028; this teaching map uses 2026–2027 requirements.

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