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PDF Essentials of Statistics

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Nguyễn Gia Hào

Academic year: 2023

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Probability space, probability function, sample space, event

Conditional probability

In the French Open final, Nadal will play the winner of the semi-final between Federer and Davydenko. The chance that Nadal can beat Federer is estimated at 51%, while the chance that Nadal can beat Davydenko is estimated at 80%.

Independent events

The Inclusion-Exclusion Formula

We want to calculate the probability P(B) of the event that all four suits appear among the 5 selected cards. To this end, let A1 be the event that none of the chosen cards are spades.

Binomial coefficients

For example, the number of subsets with 5 elements (poker hands) of a set with 52 elements (a deck of cards) is equal to 52. An easy way to remember the binomial coefficients is to arrange them in Pascal's triangle where each number is equal to the sum of the numbers immediately above:.

Multinomial coefficients

P(X =x): the probability that X takes on the value x∈R, P(X < x): the probability that accepts, etc.

The distribution function

Discrete random variables, point probabilities

Continuous random variables, density function

Continuous random variables, distribution function

Independent random variables

Roll a red die and a black die and consider the random variables X: the number of cups on the red die,. In contrast, X and Dice are not independent since information about Z provides information about X (if, for example, Z has the value 10, then X must have one of the values ​​4, 5, and 6).

Random vector, simultaneous density, and distribution function

Variance and standard deviation of random variables

Example (computation of expected value, variance, and standard deviation)

Estimation of expected value µ and standard deviation σ by eye

Addition and multiplication formulae for expected value and variance

Covariance and correlation coefficient

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The Law of Large Numbers

The Central Limit Theorem

Example (distribution functions converge to Φ)

Mean value

Empirical variance and empirical standard deviation

The larger the empirical standard deviations, the more "spread" the observations are around the mean valuex.¯.

Empirical covariance and empirical correlation coefficient

Significance probability and significance level

If P is greater than α, then H0 is accepted (and we say "H0 is accepted at significance level α" or "H0 cannot be rejected at significance level α").

Errors of type I and II

Example

Description

Point probabilities

Expected value and variance

Significance probabilities for tests in the binomial distribution

The normal approximation to the binomial distribution

Can the company now reject the manufacturer's claim that the probability of failure is at most one sixth.

Estimators

Assuming it is within two standard deviations of , we can conclude that it is between 10% and 50%.

Confidence intervals

So we can say with 95% certainty that between 52% and 72% of the electorate will vote for the Green Party in the next election.

Description

Point probabilities

Expected value and variance

Addition formula

Significance probabilities for tests in the Poisson distribution

Example (significant increase in sale of Skodas)

The binomial approximation to the Poisson distribution

The normal approximation to the Poisson distribution

Example (significant decrease in number of complaints)

Estimators

Confidence intervals

Description

Point probabilities and tail probabilities

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Expected value and variance

Description

Point probabilities and tail probabilities

Expected value and variance

The binomial approximation to the hypergeometrical distribution

The normal approximation to the hypergeometrical distribution

Parameters

Description

Point probabilities

Estimators

Description

Point probabilities

Expected value and variance

Estimators

Description

Density and distribution function

Expected value and variance

Description

Density and distribution function

The standard normal distribution

Properties of Φ

Estimation of the expected value µ

Estimation of the variance σ 2

Confidence intervals for the expected value µ

Confidence intervals for the variance σ 2 and the standard deviation σ

Addition formula

Student’s t distribution

In practice, the density is not used, but the distribution function is found in Table B.3. The graph below shows the density of this distribution with df = 1,2,3 degrees of freedom and the additional density ϕ(x) of the standard normal distribution.

Fisher’s F distribution

In practice, one does not use the density, but instead looks up the distribution function in table B.4. The significance probability now appears from the following table, where Φ is the distribution function of the standard normal distribution (table B.2).

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2) Table B.4, under df = 10 − 1 = 9 degrees of freedom, shows that t 0.975 = 2.26 (see also section 15.8)
2) Table B.4, under df = 10 − 1 = 9 degrees of freedom, shows that t 0.975 = 2.26 (see also section 15.8)

Example

The probability of significance is read from the table below where Φ is the distribution function of the standard normal distribution (Table B.3).

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Example (comparison of two expected values)

Two examples (comparison of mean values from three samples)

The assumption of normal distribution

Standardized residuals

Example (women with five children)

Test the hypothesis H0 that, at each birth, the probability of a boy is the same as the probability of a girl. We note that it is the figures of women with five children of the same sex that are extreme and make the statistic large.

Example (election)

By looking up in Table B.3 under the χ2 distribution withdf = 8−1 = 7 degrees of freedom, it is only seen that the significance probability is below 50%. So we have no statistical evidence to conclude that the popularity of the parties has changed.

Example (deaths in the Prussian cavalry)

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Standardized residuals

Example (students’ political orientation)

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Fisher’s exact test for 2 × 2 tables

The conditional probability of obtaining exactly the 2×2 table above, given that the row sums are R1 and R2, and that the column sums are S1 and S2, is It is then necessary that the 2×2 table be written in such a way that the observed numbers in the diagonal are greater than the expected numbers (this can always be achieved by switching the rows if necessary).

Example (Fisher’s exact test)

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Example

If we do not test H0 against a certain alternative hypothesis, the null hypothesis is rejected if the minimum := min{t+, t−} is extremely small. Conclusion: The test shows that the null hypothesis H0 must be rejected against the alternative hypothesis H1 at a significance level of 5%.

The normal approximation to Wilcoxon’s test for one set of observations

Wilcoxon’s test for two sets of observations

If we do not test H0 against some alternative hypothesis, the null hypothesis is rejected if it is the minimum. If it is less than or equal to the table value, H0 is rejected at significance levelα= 10%.

The normal approximation to Wilcoxon’s test for two sets of observations

Estimation of the parameters β 0 and β 1

The distribution of the estimators

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Predicted values y ˆ i and residuals e ˆ i

Estimation of the variance σ 2

Confidence intervals for the parameters β 0 and β 1

The determination coefficient R 2

Predictions and prediction intervals

Overview of formulae

Example

How to read the tables

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Table B.8 and Table B.9 give critical values for Wilcoxon’s tests for one and two sets of observa- observa-tions
Table B.8 and Table B.9 give critical values for Wilcoxon’s tests for one and two sets of observa- observa-tions

The standard normal distribution

Student’s t distribution (values x with F Student (x) = 0.600 etc.)

Fisher’s F distribution (values x with F Fisher (x) = 0.90)

Fisher’s F distribution (values x with F Fisher (x) = 0.95)

Fisher’s F distribution (values x with F Fisher (x) = 0.99)

Wilcoxon’s test for one set of observations

Wilcoxon’s test for two sets of observations, α = 5%

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Gambar

2) Table B.4, under df = 10 − 1 = 9 degrees of freedom, shows that t 0.975 = 2.26 (see also section 15.8)
Table B.8 and Table B.9 give critical values for Wilcoxon’s tests for one and two sets of observa- observa-tions

Referensi

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