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A Level Maths ( Stats) > Chapter 1 Data collection > Flashcards

Chapter 1 Data collection Flashcards

1
Q

What is a population?

Give and example and what this could mean?

A

A population is the whole set of items of interest.

A population could be items produced by a factory.
This is known as raw data.

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2
Q

What is a census?

A

A census observes or measures every member of the population.

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3
Q

What is a sample?

A

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

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4
Q

What is one advantage of a census?

A
  • It should give a completely accurate result.
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5
Q

what are 4 disadvantages of censuses?

A
  • Time consuming and expensive.
  • Cannot be used when the testing destroys the item.
  • Time consuming to process large quantities of data.
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6
Q

What is the advantages of a sample?

A
  • Less time consuming and more expensive than a census.
  • Fewer people have to respond.
  • Less data to process than a census.
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7
Q

What are the disadvantages of a sample?

A

-The data may not be as accurate

  • The sample may not be large enough to give information about sub groups of the population.
    (sample may be too small).
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8
Q

What are sampling units?

A

The individual units in a sample.

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9
Q

What is a sampling frame?

A

A numbered list with all the individual sampling units.

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10
Q

What is particular about random sampling?

What does this do?

A

Every member of the population has an equal chance of being selected.

This helps to remove bias from a sample.

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11
Q

What are the 3 methods of random sampling?

A

1-Simple random sampling
2-Systematic sampling
3- Stratified sampling

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12
Q

How to simple random sampling work?

A

To carry out simple random sampling you need a sampling frame, a list of people or things.

Each person or thing is given a number.

And a selection of numbers is chosen at random.

Generate a number through a calculator or other random method

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13
Q

What are the two ways of choosing the numbers in simple random sampling.

A
  • Method 1- Generating random numbers using a calculator or computer.
  • Method 2- Lottery sampling, members of sampling frame written on tickets.
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14
Q

What is the particular thing about systematic sampling?

A

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

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15
Q

How is systematic sampling done on a population 200 and you needed a sampling size of 20.

A

200/20=10
You would take every 10th Person

You would take a random starting point between the interval eg 1-10

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16
Q

What is the key of stratified sampling?

A

The population is divided into mutually exclusive strata (Males and Females for example) and a random sample is taken from each.

17
Q

What is the formula for the number of people sampled in a stratum?

A

Number in stratum/number in population x overall sample size.

18
Q

What are the advantages of simple random sampling?

A
  • Free of bias.
  • Easy and cheap to implement for small populations.
  • Each sampling unit has an equal chance of selection.
19
Q

What are the disadvantages of simple random sampling?

A
  • Not suitable when population size is large

- Sampling frame is needed.

20
Q

What are the advantages of systematic sampling?

A
  • Simple and quick to use.

- Suitable for large samples and large populations.

21
Q

What are the disadvantages of systematic sampling?

A
  • A sampling frame is needed

- Can introduce bias is sampling frame is not random.

22
Q

What are the advantages of stratified sampling?

A
  • sample represents the population better.

- Guarantees proportional. representation, of groups, within a population.

23
Q

Disadvantages of stratified sampling?

A
  • Population musty be clearly classified into distinct strata.
  • Selection within each stratum has same disadvantages of simple random sampling.
24
Q

What are the two types of non-random sampling?

A

Quota sampling and opportunity sampling.

25
Q

What is particular about quota sampling?

A

In quota sampling an interviewer selects a sample that represents the characteristic of the whole population.
Until the quota is full.

26
Q

How does quota sampling work?

What does the interviewer do?

A

step 1 -The population is divided into groups according to a given characteristic.
The size of each group should determine the proportion that should have that characteristic.

step 2 -Interviewer meets people assesses group and allocates into appropriate quota.

-Step 3 this continues until all quotas have been filled.

27
Q

What happens if the Quota is full or someone refuses to be sampled?

A

They are ignored and the interviewer moves on to the next person.

28
Q

What is opportunity sampling also called?

A

Convenience sampling.

29
Q

What is particular about opportunity sampling?

A

Consists of taking a sample from those people who are around when you are taking the study and fit the criteria you set out.

30
Q

What are the advantages of Quota sampling?

A
  • Allows a small sample to be representative of the whole population.
  • No sampling frame required

–Allows easy comparison between groups in a population.

31
Q

What are the disadvantages of quota sampling?

A
  • Introduces bias
  • Population must be divided into groups which can introduce bias.
  • Increasing scope of study increases number of groups, which adds time and expense.
  • Non responses are not recorded.
32
Q

What are the advantages of opportunity sampling?

A
  • Easy to carry out

- Inexpensive

33
Q

What are the disadvantages of opportunity sampling?

A

unlikely to provide representative sample.

  • Highly dependent on individual researchers.
34
Q

How can you do quota sampling in context?

4 steps

A

1-Divide the population into groups according to given characteristics.
2-The size of each group determines the proportion of the sample that should have that characteristic.
3-The interviewer should assess which group people fall into, as part of the interview.
4-Once a quota has been filled, no more people in that group are interviewed.

35
Q

How could you do opportunity sampling in context?

A

Only sample the people who are available at the time the study is carried out, e.g. the first 40 shoppers who are available to be interviewed.

36
Q

What is a discrete variable?

A

A discrete variable can only take specific variables.

37
Q

What is a continuous variable?

A

A variable that can take any value in a given range.

A Level Maths ( Stats) (12 decks)

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