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Edexcel Alevel: Maths
Statistics
Data Collection
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Cards (43)
Define Population:
The whole set of items that are of interest
Define Raw Data:
Data obtained from a population
Define Census:
Data that measures every member of a population
Define Sample:
A selection of observations taken from a subset of the population used to estimate information about the population as a whole
Outline the advantage of a census:
It gives a completely accurate result
Outline the disadvantages of a census:
Time consuming
Expensive
Cannot be used when the testing process destroys the items
It is difficult to process a large quantity of data
Outline the advantages of a sample:
Less time consuming
Cheaper
Fewer responses are needed
Less data is processed
Outline the disadvantages of a sample:
Data may not be as accurate
The sample may not be large enough to be representative of the whole population
Define Sampling Units:
The individual units of a population
Define Sampling Frame:
Sampling units individually named or numbered to form a list
Name the three types of random sampling:
Simple random sampling
Systematic sampling
Stratified sampling
Define Simple random sampling:
A sampling technique where every element in the set has an equal chance of being selected
Define Systematic sampling:
A sampling technique where the elements are chosen at regular intervals from an ordered list
Define Stratified sampling:
A sampling technique where the population is divided into exclusive strata and a random sample is taken from each
Outline the advantages of simple random sampling:
Non-bias
Easy and cheap for small samples and populations
Each sampling unit has a known and equal chance of being selected
Outline the disadvantages of simple random sampling:
Not suitable for large samples and populations
Sampling frame needed
Name the two methods of choosing the numbers from a sampling frame in simple random sampling:
Generating random numbers
Lottery sampling
Describe how a calculator is used for generating random numbers for simple random sampling:
Each sampling unit from a sampling frame is numbered.
Use a calculator to generate a set of numbers.
Select the sampling units who correspond to the numbers generated.
Describe how lottery sampling is used for simple random sampling.
The sampling units from a sampling frame are written on identical cards.
The cards are put into a hat.
The required number of sampling units needed are drawn from the hat.
The card of the sampling unit drawn out are selected.
Outline the advantages of systematic sampling:
Simple and quick to use
Suitable for large samples and populations
Outline the disadvantages of systematic sampling:
Sampling frame needed
Can be biased if the sampling frame is not random
The formula for how to work out the value of the regular intervals for systematic sampling:
The population
/
the sample size
The first person selected in
systematic sampling
is chosen
randomly
, then the regular intervals continue
Outline the advantages of stratified sampling:
Accurately reflects population structure
Guarantees proportional representation of all groups within a population
analyse specific groups within a population
observe relationships between groups
Outline the disadvantages of stratified sampling:
The population must be clearly classified into distinct strata
Same disadvantages as simple random sampling within each stratum
Name the two types of non-random sampling:
Quota sampling
Opportunity sampling
Define Quota sampling:
A sampling technique where the sample selected reflects the characteristics of the whole population
Define Opportunity sampling:
A sampling technique where the sample is taken from people who are available at the time of study and who fits the criteria needed
Outline the advantages of quota sampling:
Allows a small sample to be representative of the whole population
No sampling frame needed
can be quick
can be easy
can be cheap
Allows comparisons between different groups within the population
Outline the disadvantages of quota sampling:
Bias
The population must be divided into groups which can be inaccurate
-
not possible to estimate sampling errors
A more in depth study can be time consuming as it increases the number groups
Non-responses are not recorded
Outline the advantages of opportunity sampling:
Easy
Cheap
Outline the disadvantages of opportunity sampling:
Results can be unrepresentative of the whole population
Highly dependent on the individual researcher
Define Qualitative data:
Non numerical data
Define Quantitative data:
Numerical data
Define Discrete data:
Data which can only take specific values
Define Continuous data:
Data which can take any value in a given range
What is the limitation for continuous data?
How accurately it is measured
Define Class boundaries:
The maximum and minimum values in each group
Define the Midpoint:
The mean
/
average of the class boundaries
Define the Class Width:
The difference between the upper and lower class boundaries
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