Data Collection and Interpretation Flashcards
Population?
- The whole set of items
Sample?
- Subset of population
- Intended to represent the population
Sampling unit?
- Each individual item in population
Census?
- Data collected from the whole population
Census advantages and disadvantages
Advantage:
* Completely accurate result
Disadvantage:
* Time consuming
* Expensive
* Cannot be used when testing involves destruction
* Large volume of data to process
Parameters?
- A calculation of a sample/population
Sampling error?
- The difference between the actual value of a parameter and the value derived from a sample
What can result in a biased sample?
- Sample not representative of population
- Wrong person asking questions
- Small sample size
Random vs non-random sampling?
- Random: every item has an equal chance of being selected for the sample
- Non-random: sample selection based on other factors
Simple random sampling method?
- Each item in sampling frame has identifying number
- Use random number generator/lottery sampling
Simple random sampling advantages/disadvantages?
Advantages:
* Bias free
* Easy/cheap
* Equal chance of being selected
Disadvantages:
* Not suitable for large population size
* Sampling frame needed
Systematic sampling method?
- Take every kth element
k = pop size/samp size
Systematic sampling advantages/disadvantages?
Advantages:
* Simple
* Suitable for large samples
Disadvantages:
* Sampling frame needed
* Can introduce bias if sampling frame is not random
Not random if there are patterns in data e.g. students are in order of ability
Stratified sampling method?
- Population divided into groups (strata) and simple random sampling carried out in each group
- samp size/pop size simple randomly ampled from each strata
Stratified sampling advantages/disadvantges?
Advantages:
* Reflects population structure
* Guarantees proportional representation of groups within population
Disadvantages:
* Pop must be clearly classified into distinc strata
* Same as random sampling
Oppportunity/Convenience sampling method?
- Sample taken from people who are available at the time of study and meet criteria
Opportunity/Convenience sampling advantages/disadvantages?
Advantages:
* Easy
* Inexpensive
Disadvantages:
* Unlikely to provide a representative sample
* Highly dependent on individual researcher
Cluster sampling method?
- Define each cluster
- Collect samples from each cluster
Cluster sampling advantages/disadvantages?
Advantages:
* No sampling frame
* Inexpensive
Disadvantages:
* Unlikely to provide a representative sample because clusters have similar characteristics = overrepresentation within a cluster
Quota sampling method?
- Pop. divided into groups according to characteristics
- Interviewer selects the actual sampling method
Quota sampling advantages/disadvantages?
Advantages:
* Allows small sample to still be representative of population
* No sampling frame needed
* Easy/inexpensive
* Allows for easy comparison between groups in population
Disadvantages:
* Non-random sampling can introduce bias
* Population has to be divided into groups (may be inaccurate)
