Flashcards in Statistics As Deck (90)

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## Population

### The whole set of items that are of interest

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## Census

### Observes/Measures every member of a population

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## Sample

### A selection of observations taken from a subset of the population which is used to find out information about the population as a whole

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## Ad, Disad: Census

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Ad: It should give a completely accurate result

Dis: Time consuming and expensive

Cannot be used when the testing process destroys the item

Hard to process large quantity of data

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## Ad, Disad: Sample

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Ad: less time consuming and expensive than census

Fewer people have to respond

Less data to process than census

Dis: The data may not be as accurate

The sample may not be large enough to give information about small subgroups of the population

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## Sampling units

### Individual units of a population

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## Sampling frame

### Sampling units of a population that are named/numbered to form a list

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## What are the 3 methods of random sampling?

###
1) Simple random

2) Systematic

3) Stratified

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## What does random sampling do?

### Every member of the population has an equal chance of being selected. Therefore should be representative of the population. Also helps to remove bias from a sample.

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## How do you carry out simple random sampling?

### Need a sampling frame. Each unit is allocated a unique number and a selection of these numbers is chosen at random

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## What are the ways of picking a random unit in simple random sampling?

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1) Generating random numbers (using calculator, computer etc.)

2) Lottery sampling - The members of the sampling frame could be written on tickets and placed into a 'hat'. The required number of tickets is then drawn out

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## Systematic sampling

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The required elements are chosen at regular intervals from an ordered list. Eg.

Sample size: 20

Population: 100

100/20 = 5. Every 5th person is picked.

The first person to be chosen is picked at random

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## Stratified sampling

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the population is divided into mutually exclusive strata and a random sample is taken from each

The proportion of each strata should be the same.

No. sampled in stratum = (No. in strata / No. in population) * Overall sample size

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## Ad, Disad: Simple random sampling

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Ad: Free of bias

Easy and cheap to implement for small populations and small samples

Each sampling unit has a known and equal chance of selection

Dis: Not suitable when the pop. size or sample size is large

a sampling frame is needed

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## Ad, Disad: Systematic sampling

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Ad: Simple and quick to use

Suitable for large samples and populations

Dis: A sampling frame is needed

It can introduce bias if the sampling frame is not random

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## Ad, Disad: Stratified sampling

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Ad: Sample accurately reflects the population structure

Guarantees proportional representation of groups within a population

Dis: Population must be clearly classified into distinct strata

Selection within each stratum suffers from the same disad. as simple random sampling

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## Two types of non-random sampling:

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1) Quota sampling

2) Opportunity sampling

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## Quota sapling

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An researcher selects a sample that reflects the characteristics of the whole population

the population is divided into groups according to a given characteristic. The size of each group determines the proportion of the sample that should give that characteristic

As an interviewer, you would meet people, assess their group and then allocates them into the appropriate quota

This continues until all quotas have been filled. If a person refuses to be interviewed or the quota is full then you ignore them

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## Opportunity sampling

### Taking the sample from people who are available at the the time of the study, who fit the criteria you are looking for

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## Ad. Disad; Quota

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Ad: Allows a small sample to still be representative of the population

No sampling frame required

Quick, easy and inexpensive

Allows for easy comparison between different groups within a population

Dis: Non-random samples can introduce bias

Population must be divided into groups, which can be costly or inaccurate

Increasing scope of study increase number of groups which adds time and expense

Non-responses are not recorded as such

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## Ad. Disad; Opportunity

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Ad: Easy to carry out

Inexpensive

Dis: Unlikely to provide a representative sample

Highly dependant on individual researcher

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## Quantitative data

### Numerical data

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## Qualitative data

### Non-numerical

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## Continuous

### Take any value in a given range

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## Discrete

### Only specific values

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##
Explain briefly what you understand by

(i) a statistical experiment [1]

### A test/investigation adopted for collecting data to provide evidence for or against a hypothesis

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##
Explain briefly what you understand by

(ii) an event. [1]

### Sub-set of of possible outcomes of an experiment

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## State one advantage and one disadvantage of a statistical model. [2]

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Ad: Quick, cheap, vary parameters/predict

Dis: Does not replicate real-world situation in every detail

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## Define Hypothesis Test

### A statistical test that is used to determine whether there is enough evidence in a sample of data to infer that a certain condition is true for the entire population

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