General Statistics Flashcards
To learn about statistics
Population definition
The whole set of items that are of interest
Census definition
An observation or measurement of every member of a population
Sample definition
A selection of observations taken from a subset of the population which is used to find out information about the population as a whole
Census advantages
It should give a completely accurate result
Census disadvantage
- Time consuming and expensive
- Cannot be used when the testing process destroys the item
- Hard to process large quantity of data
Sample advantages
- Less time consuming and expensive than a census
- Fewer people have to respond
- Less data to process than in a census
Sample 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
How to increase the accuracy of a sample
Increase the number of size of the sample - especially if the population is varied (more variety needs a larger sample)
Sampling units definition
Individual units of a population
Sampling frame definition
A numbered/named list of sampling units
Simple random sampling definition
A sampling system whereby each sampling unit has an equal chance of being selected
Two methods of choosing sampling units in a simple random sample
Random number generation and lottery
Lottery sampling definition
Randomly picking out certain names (e.g. names in a hat)
Systematic sampling definition
Choosing the required sampling units at regular intervals from an ordered sampling frame - the first sampling unit should be selected at random within the first interval, and then it is continued from them
Stratified sampling definition
Dividing the population into mutually exclusive strata (e.g. male/female) and a proportional random sample is taken from both
Advantages of simple random sampling
- Free of bias
- Easy and cheap to implement for small samples
- Each sampling unit has a known and equal chance of prediction
Disadvantages of simple random sampling
- Not suitable when the population size or sampling size is large
- Requires a sampling frame
Advantages of systematic sampling
- Simple and quick to use
- Suitable for large samples and large populations
Disadvantages of systematic sampling
- Requires a sampling frame
- Can introduce bias if sampling frame is not random
Quota sampling definition
Selecting a sample that reflects the characteristics as a whole by dividing the populations into groups based on a given characteristic then allocate each individual in a group into an appropriate quote
Opportunity sampling definition
Taking the sample from people who are available at the time the study is performed assuming they fulfil the criteria
Advantages of quota sampling
- Allows a small sample to be representative of the population
- No sampling frame is required
- Quick, easy and inexpensive
- Allows for easy comparison between different groups within a population
Disadvantages of quota sampling
- Non-random sampling can introduce bias
- Population must be divided into groups which can be costly or inaccurate
- Increasing scope of study increases number of groups, which adds time and expense
- Non-responses are ignored rather than recorded as such
Advantages of opportunity sampling
- Easy to carry out
- Inexpensive
