3.4 Optional application 2 – statistics

3.4.1 SA: Discrete random variables (DRVs) and expectation

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SA1Understand DRVs with distributions given in the form of a table or function.
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SA2Evaluate probabilities for a DRV.
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SA3Evaluate measures of average and spread for a DRV to include mean, variance, standard deviation, mode and median.
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SA4Understand expectation and know the formulae: EX=xipi ; EX2=xi2pi ; VarX=EX2-(EX)2
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SA5

Understand expectation of linear functions of DRVs and know the formulae:

EaX+b=aEX+b and VaraX+b=a2Var(X)

Know the formula EgX=g(xi)pi

Find the mean, variance and standard deviation for functions of a DRV such as E5X3,E18X-3,Var(6X-1)

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SA6

Know the discrete uniform distribution defined on the set 1,2,,n . Understand when this distribution can be used as a model.

3.4.2 SB: Poisson distribution

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SB1

Understand conditions for a Poisson distribution to model a situation. Understand terminology X~Po(λ) .

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SB2Know the Poisson formula and calculate Poisson probabilities using the formula or equivalent calculator function.
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SB3

Know mean, variance and standard deviation of a Poisson distribution.

Use the result that, if X~Poλ then the mean and variance of X are equal.

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SB4Understand the distribution of the sum of independent Poisson distributions.
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SB5

Formulate hypotheses and carry out a hypothesis test of a population mean from a single observation from a Poisson distribution using direct evaluation of Poisson probabilities.

3.4.3 SC: Type I and Type II errors

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SC1

Understand Type I and Type II errors and define in context. Calculate the probability of making a Type I error from tests based on a Poisson or Binomial distribution.

Calculate probability of making Type I error from tests based on a normal distribution.

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SC2

Understand the power of a test. Calculations of P(Type II error) and power for a test for tests based on a normal, Binomial or a Poisson distribution.

3.4.4 SD: Continuous random variables (CRVs)

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SD1Understand and use a probability density function, f(x) , for a continuous distribution and understand the differences between discrete and continuous distributions. Understand and use distributions of random variables that are part discrete and part continuous.
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SD2Find the probability of an observation lying in a specified interval.
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SD3Find the median and quartiles for a given probability density function, f(x) .
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SD4

Find the mean, variance and standard deviation for a given pdf, f(x) . Know the formulae

EX=xfxdx , EX2=x2fxdx , VarX=EX2-(EX)2

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SD5

Understand the expectation and variance of linear functions of CRVs and know the formulae:

EaX+b=aEX+b and VaraX+b=a2Var(X)

Know the formula EgX=gxf(x)dx

Find the mean, variance and standard deviation of functions of a continuous random variable such as

E5X3,E18X-3,Var(6X-1)

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SD6

Understand and use a cumulative distribution function, F(x) . Know the relationship between f(x) and F(x) .

Fx=-xftdt and fx=ddxFx

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SD8

Know that if X and Y are independent (discrete or continuous) random variables then EX+Y=EX+EY and VarX+Y=VarX+Var(Y)

3.4.5 SE: Chi squared tests for association

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SE1Construction of n × m contingency tables.
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SE2

Use of (Oi-Ei)2Ei as an approximate χ2 statistic with appropriate degrees of freedom.

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SE3Know and use the convention that all Ei should be greater than 5.
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SE4Identification of sources of association in the context of a question.
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SE5Knowledge of when and how to apply Yates’ correction.

3.4.6 SF: Exponential distribution

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SF1Know the conditions for an exponential distribution to be used as a model. Know the probability density function, f(x) , and the cumulative distribution function, F(x) , for an exponential distribution.
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SF2Calculate probabilities for an exponential distribution using F(x) or integration of f(x)
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SF3Know proofs of mean, variance and standard deviation for an exponential distribution.
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SF4Understand that the lengths of intervals between Poisson events have an exponential distribution.

3.4.7 SG: Inference – one sample t- distribution

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SG1

Test for the mean of a normal distribution with unknown variance using a

t with appropriate degrees of freedom.

3.4.8 SH: Confidence Intervals

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SH1

Construct symmetric confidence intervals for the mean of a normal distribution with known variance.

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SH2Construct symmetric confidence intervals from large samples, for the mean of a normal distribution with unknown variance.
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SH3Make inferences from constructed or given confidence intervals.
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SH4Construct symmetric confidence intervals from small samples, for the mean of a normal distribution with unknown variance using the t -distribution.