Studied by 3 people
Population
A whole set of items that are of interest
Census
Observes or measures every member of a population
Sample
A selection of observations taken from a subset
Advantage of a census
Should give a completely accurate results
3 disadvantages of a census
Time consuming
Cannot be used when the testing process destroys the item
Hard to process a large quantity of data
3 advantages of a sample
Less time consuming and expensive than a census
Fewer people have to respond
Less data to process than in a census
2 disadvantages of a sample
Data may not be accurate enough, Sample may not be large enough to give information about small sub-groups of the population
Sample units
Individual units of a population
Samping frame
A list of sample units
A simple random sample if size n
One where ever sample of size n has an equal chance of being selected
In stratified sampling
Population is divided into mutually exclusive strata and a random sample is taken from each
In systematic sampling
Required elements are chosen at regular intervals form an ordered list
3 advantages of simple random sampling
Free of bias, Easy and cheap to implement for small populations and samples, Each sampling unit has known and equal chance of selection
2 disadvantages of simple random sampling
Not suitable when the population size or the sample size is large, A sampling frame is needed
2 advantages of systematic sampling
Simple and quick to use, Suitable for large samples and large populations
2 disadvantages of systematic sampling
A sampling frame is needed, It can introduce bias if the sampling frame is not random
2 advantages of stratified sampling
Sample accurately reflects the population, Guarantees proportional representation of groups within a population
2 disadvantages of stratified sampling
Population must be clearly classified into district data, Selection within each stratum suffers from the same disadvantages as a simple random sampling
An example of a simple random sampling is
A jury
An example of a systematic sampling is
Every house number ending in 1
An example of stratified sampling is
Bhasvic asking 50 first years and 40 second years. (Bhasvic has 1500 first years and 1200 second years)
In quota sampling
An interviewer selects a sample that reflects the characteristics of the population
Opportunity sampling
Taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking for
4 advantages of quota sampling
Allows a small sample to still be representative of the the population, No sampling frame required, Quick, Allows for easy comparison between different groups within a population
4 disadvantages of quota sampling
Non-random sampling can introduce bias, Population must be divided into groups, Increasing scope of study increases number of groups, Non-responses are not recorded as such
2 advantages of oppurtunity sampling
Easy to carry out, Inexpensive
2 Disadvantages of oppurtunity sampling are
Unlikely to provide a representative sample, Highly dependent on individual researcher
An example of quota sampling is
For maths
An example of oppurtunity samping
Asking women aged between 19 and 25 outside Brighton train station between 10am and 11am
Quantatitve variables
Variables with numerical observations
Quantative data
Data with numerical observations
Qualatitive variables
Variables with non-numerical observations
Qualatitive data
Data with non-numerical observations
Continuous variable
Can take any value in a given range
Discrete variable
Can take only specific values in a given range
Note 
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