S2 Definitions

Question 1

When do you use a Binomial Distribution?

Answer 1

1. When there a fixed number of trials
2. Each trial must be success or failure
3. The trials must be independent
4. The probability of success is constant

Question 2

When do you use a Poisson Distribution?

Answer 2

1. When the event occurs singling in time
2. the events must be independent of each other
3. the event must occur at a constant rate in the sense that the mean number of occurrences in the interval is proportional to the length of the interval.

Question 3

When is it suitable to approximate poisson by normal?

Answer 3

1. when the parameter is greater then 10

Question 4

When can you approximate binomial by normal?

Answer 4

1. When the number of trials is large and p is close to 0.5

Question 5

When can you approximate Binomial by Poisson?

Answer 5

When the number of trials is large and the probability is small,
and when np is less then or equal to 10.

Question 6

Population

Answer 6

this is a collection of individual items

Question 7

sample

Answer 7

a sample is a selection of individual members or items from a population

Question 8

a finite population

Answer 8

a finite population is one in which each individual member can be given a number

Question 9

an infinite population

Answer 9

an infinite population is one in which it is impossible to number each member

Question 10

Sampling unit

Answer 10

a sampling unit is an individual member of a population

Question 11

sampling frame

Answer 11

this is a list of the sampling units used in practice to represent a population

Question 12

statistic

Answer 12

this is a quantity calculated solely from the observations in a sample

Question 13

Sampling distribution

Answer 13

a statistic has a sampling distribution that is defined by giving all possible values of the statistic and probability of each occurring

Question 14

Census

Answer 14

a survey of the entire population

Question 15

advantages of a census

Answer 15

1. every single member of the population is used
2. it is unbiased
3. it gives an accurate answer

Question 16

disadvantages of a census

Answer 16

1. it takes a long time to do
2. it is costly
3. it is often difficult to ensure that the whole population is surveyed

Question 17

advantages of sampling

Answer 17

1. cheaper than a census
2. better when testing items results in their destruction
3. data is usually for readily available

Question 18

disadvantages of sampling

Answer 18

1. uncertainty, as there will be a natural variation between samples
2. the sample may not be representative of the population and therefore will be biased,
   bias occurs if a person has personal feelings about the topic being surveyed, or a greater interest in it then the average person.

Question 19

What is the actual significance?

Answer 19

The probability of rejecting the null hypothesis