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Maths AS Statistics > Data Sampling > Flashcards

Data Sampling Flashcards

1
Q

Population

A

Whole set of items that are of interest

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2
Q

Census

A

Observes and measures every member of the population

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3
Q

Sample

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

Advantages and Disadvantages of using a Census

A

Advantages
- It should give a completely accurate result

Disadvantages

  • Time consuming and expensive
  • Cannot be used when testing process destroys the item
  • Hard to process large quantity of data
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5
Q

Advantages and Disadvantages of using a Sample

A

Advantages

  • Less time consuming and expensive
  • Fewer people have to respond
  • Less data to process

Disadvantages

  • The data may not be as accurate
  • The sample may not be large enough to give information about small sub-groups of the population
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6
Q

Sampling Unit

A

Individual units of a population

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7
Q

Sampling Frame

A

Sampling units of a population are individually named or numbered to form a list

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8
Q

Simple Random Sample

A

every sample of size n has an equal chance of being selected

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9
Q

Systematic Sampling

A

the required elements are chosen at regular intervals from an ordered list

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10
Q

Stratified Sampling

A

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

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11
Q

The number sampled in a stratum =

A

number in stratum/number in population x overall sample size

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12
Q

Advantages and Disadvantages of Simple Random Sampling

A

Advantages

  • Free of bias
  • Cheap and easy to implement for a small population and small samples
  • Each sampling unit has a known and equal chance of selection

Disadvantages

  • Not suitable when the population size or the sample size is large
  • A sampling frame is needed
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13
Q

Advantages and Disadvantages of Systematic Sampling

A

Advantages

  • Simple and quick to use
  • Suitable for large samples and large populations

Disadvantages

  • Sampling frame needed
  • It can introduce bias if the sampling frame is not random
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14
Q

Advantages and Disadvantages of Stratified Sampling

A

Advantages

  • Sample accurately reflects the population structure
  • Guarantees proportional representation of groups within a population

Disadvantages
- Population must be clearly classified into distinct strata
Selection within each stratum suffers from:
- Not suitable when the population size or the sample size is large
- A sampling frame is needed

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15
Q

Quota Sampling

A

an interviewer/researcher selects a sample that reflects the characteristics of the whole population

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16
Q

Opportunity Sampling

A

consists of taking the sample from people who are available at the time of the study and fit the criteria you are looking for

17
Q

Advantages and Disadvantages of Quota Sampling

A

Advantages

  • 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

Disadvantages

  • Non-random sampling can introduce bias
  • Population must be divided into groups, which can be costly and inaccurate
  • Non-responses are not recorded as such
18
Q

Advantages and Disadvantages of Opportunity Sampling

A

Advantages

  • Easy to carry out
  • Inexpensive

Disadvantages

  • Unlikely to provide a representative sample
  • Highly dependent on individual researcher
19
Q

Quantitative data

A

data associated with numerical observations

20
Q

Qualitative data

A

data associated with non-numerical observations

21
Q

Continuous variable

A

a variable that can take any value in a given range

22
Q

Discrete variable

A

a variable that can take only specific values in a given range

23
Q

If data is coded using the formula:
y = x-a/b
The mean of the coded data is given by:

A

ȳ = x̄-a/b

24
Q

The mean of the coded data is given by ȳ= x̄-a/b

The original data is given by:

A

x̄ = bȳ+a

25
Q

Standard deviation of the coded data

A

σy = σx/b

26
Q

Taking a Simple Random Sample (4 marks)

A
  1. Identify the sampling frame
  2. Assign numbers to units 1 to n
  3. Use a random number generator and select sample numbers between 1 and n
  4. Use units corresponding to the numbers selected

Maths AS Statistics (3 decks)

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