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Applied Statistics Using SPSS, STATISTICA, MATLAB and R

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436 Appendix B - Distributions<br />

For large N, sampling without replacement is similar to sampling with<br />

replacement. Notice the asymptotic behaviour of the finite population<br />

correction in the variance of the hypergeometric distribution.<br />

2. X ~ Bn,<br />

p ⇒ n − X ~ Bn,<br />

1−<br />

p .<br />

3. X ~ Bn1<br />

, p <strong>and</strong> Y ~ Bn2<br />

, p independent<br />

⇒ X + Y ~ Bn1<br />

+ n2<br />

, p .<br />

4. The mode occurs at µ (<strong>and</strong> at µ −1 if (n+1)p happens to be an integer).<br />

0.3<br />

0.25<br />

0.2<br />

0.15<br />

0.1<br />

0.05<br />

0<br />

b (n ,p )<br />

0 2 4 6 8 10 12 14 16 18 20 k<br />

Figure B.5. Binomial probability functions: B8, 0.5 (light grey); B20, 0.5 (dark grey);<br />

B20, 0.85 (black). The double arrow indicates the µ ±σ interval for B20, 0.5.<br />

Example B. 5<br />

Q: The cardiology service of a Hospital screens patients for myocardial infarction.<br />

In the population with heart complaints arriving at the service, the probability of<br />

having that disease is 0.2. What is the probability that at least 5 out of 10 patients<br />

do not have myocardial infarction?<br />

A: Let us denote by p the probability of not having myocardial infarction, i.e.,<br />

p = 0.8. The probability we want to compute is then:<br />

P<br />

10<br />

= ∑ b10<br />

k = 5<br />

, 0.<br />

8<br />

( k)<br />

= 1−<br />

B10,<br />

0.<br />

8 ( 4)<br />

B.1.6 Multinomial Distribution<br />

= 0.9936.<br />

Description: Generalisation of the binomial law when there are more than two<br />

categories of events in n independent trials with constant probability, pi (for i = 1,<br />

2, …, k categories), throughout the trials.<br />

Sample space: {0, 1, …, n} k .

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