Stats Chapter 1 Flashcards
What is a population
The whole set of items that are of interest
What’s a sample
Some subset of the population intended to represent the population
What’s a sampling unit
Each individual thing in the population that can be sampled
What’s a sampling frame
Sampling units of a population are individually named or numbered to form a list
What is a census
When data is collected from the entire population
What are the advantages of a census
Should give a completely accurate result
What are the disadvantages of a census
-time consuming and expensive
-can’t be used when testing involves destruction
-large volume of data to process
What are the advantages of a sample
Cheaper
Quicker and lesss data to process
What are the disadvantages of a sample
Data may not be accurate
Data may to be large enough to represent small sub groups
Why is random sampling a good thing
Want each thing in sampling frame to have an equal chance of being chosen in order to avoid bias
What is simple random sampling
Every sample has an equal chance of being selected
What is the method for simple random sampling
In a Sampling frame each item has an identifying number and a random number generator is used
What are the advantages of simple random sampling
Bias free
Easy and cheap to implement
Each number has a known equal chance of being selected
What are the disadvantages of simple random sampling
Not suitable when population size is large
Sampling frame is needed
What is systematic sampling
Required elements are choose at regular intervals in ordered list
What’s the method for systematic sampling
From a sampling frame items given identifying numbers and interval chosen. Random number hose in first interval then after that each interval item
What are the advantages to systematic sampling
Simple and quick to use
Suitable for large samples/populations
What are the disadvantages to systematic sampling
Sampling frame needed
Can introduce bias if sampling frame not random
What is stratified sampling
Population is divided into groups (strata) and a simple random sample is carried out in each group
Used when sample is large and population naturally divides into groups
Advantages of stratified sampling
- reflects population structure
-guarantees proportional representation of groups within population
Disadvantages of stratified sampling
-population must be clearly classified into distinct strata
-selection within each stratum suffers from same disadvantages as simple random sampling
What is quota sampling
Population divided into groups according to characteristic. A quota of items or people in each group is set to try and reflect the groups proportion in the whole population. Interviewer selects the actual sampling units
Advantages of quota sampling
- allows small sample to still be representative of whole population
-no sampling frame required
-quick easy and inexpensive - allows for easy comparison between different groups in 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 adding time or expense
-non responses are not recorded
What’s opportunity sampling
Sample taken from people who are available at the time and meet study criteria
Advantages of opportunity sampling
-Easy to carry out
-inexpensive
Disadvantages of opportunity sampling
-unlikely to provide a representative sample
-highly dependant on individual researcher
