Chapter 1 - Data Collection Flashcards
What is a Population?
A Population is the whole set of people or items that are of interest
What is a Census?
It observes or measures every member of a population
What is a sample?
Its a selection of observations taken from a subset of the population to find out info about a population as a whole
What are the advantages and disadvantages of using a census?
Advantage:
It should give a completely accurate result
Disadvantages:
- Time Consuming
- Expensive
- cant be used if the testing process destroys the item
- Hard to process large quantity of data
What are the advantages and disadvantages of using a sample?
Advantages:
- Less Time Consuming than a census
- less expensive than a census
- Fewer people have to respond
- Less data to process compared to a census
Disadvantages:
- The data may not be as accurate as a census
- the sample may not be large enough to give info about small sub-groups of the population
What are sampling units?
They’re individual units of the population e.g -> Someones name in a register
What is a sampling frame?
Its a list of sampling units which have been numbered or named individually e.g a register or list
What is Simple Random Sampling?
every sample of size n has an equal chance of being selected
How is Simple Random Sampling Carried out?
- A Sampling Frame is needed
- Each person is given a unique number (the selection of these numbers are chosen at random)
- Numbers are chosen using a (Random Number generator, computer, calculator etc) or a LOTTERY SAMPLE
To do the LOTTERY SAMPLE method numbers should be placed into a ‘hat’ and then the required amount of numbers should be pulled out.
What is Systematic Sampling?
The required number of elements are chosen at regular intervals from an ordered list e.g. Every 5th person
(the first sample should be chosen at random)
What is Stratified Sampling?
A sampling method that involves the population to be divided into mutually exclusive strata (e.g. females and males) and a random sample is taken from each
What is the formula for stratified sampling?
The number of sample in a strata
number in strata/ number in population
(answer) x overall sample size
What are the advantages and disadvantages of using a Simple Random Sampling?
Advantages:
- Free of bias
- Easy and cheap to implement for small populations and small samples
- Each sampling unit has a known and equal chance of selection
Disadvantages:
- Not suitable for when the population size or sampling size is large
- A sampling frame is needed
What are the advantages and disadvantages of using a Systematic Sampling ?
Advantages:
- Simple and quick to use
- suitable for large samples and populations
Disadvantages:
- A sampling frame is needed
- it can introduce bias if the sampling frame is not at random
What are the advantages and disadvantages of using a Stratified sampling?
Advantages:
- The sample accurately reflects the population structure
- Guarantees proportional representation of groups within a population
Disadvantages:
- The population must be clearly classified into distinct strata
- Not suitable when the population size or sample size is large
- A sampling frame is needed
What are the types of Non-Random Sampling?
Quota and Opportunity Sampling
What is quota Sampling?
its when an interviewer or researcher selects a sample that reflects the characteristics of the whole population
What is Opportunity Sampling?
it consists of taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking.
e.g first 20 people you meet outside a super market
How is quota sampling carried out?
- The pop is divided into groups to a given characteristic
- The interviewer will meet people, assess their groups and then, after interview, allocate them into the appropriate quota.
- This continues until all quotas have been filled, if someone refuses or the quota into which they fit into is full then theyre just ignored and the next person is interviewed
What are the advantages and disadvantages of using Quota sampling?
Advantages:
- Allows a small sample to still be representative of the population
- No sampling frame required
- Quick and easy and inexpensive
- allows for easy comparison between dfferent groups within a population
Disadvantages:
- 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-response are not recorded as such
What are the advantages and disadvantages of using an opportunity sampling?
Advantages;
- easy to carry out
- inexpensive
Disadvantages:
- Unlikely to provide a representative sample
- Highly dependent on individual researcher
How many types of random sampling are there?
There are 3 types:
Simple random sampling
stratified sampling
systematic sampling
What are QuanTitative Variables/ Data?
They’re variables or data associated with numerical observations
e.g. shoe size
What are QuaLitative Variables/ Data?
They’re variables or data not associated with numerical observations
e.g. Hair colour
What are continuous variables?
They’re variables that can take any value in a given range
e.g. Time, Distance (2 secs, 2.1 secs 2.01 secs etc..)
What are discrete variables?
They’re variables that can take only specific values in a given range
e.g. The number of girls in a family (you cant have 2.65 girls in a family )
What does the class boundary tell you?
It tells you the maximum and minimum values that belong to each class
What is the midpoint ?
Its the average of the class boundaries
What is the class width?
Its the difference between the upper and lower class boundaries
