Stats chapter 1

• what is a census?

  A census observes or measures every member of a population.
• What is a sample?


  A sample is a selection of observations taken from a subset of the population which is used to find out information on the population as a whole.
• what does population mean?

  A population is the whole set of items that are of interest.
• What is raw data?

  Raw data is information obtained from a population.
• What are the advantages of a census?

  An advantage of a census is it should give a completely accurate result.
• What are the disadvantages of a census?

  The disadvantages of a census are that they are time consuming and expensive, they can not be used if the testing process destroys the item and it is hard to process large quantities of data.
• What are the advantages of samples?

  The advantages of samples are that they are less time consuming and expensive than a census, fewer people have to respond and there is less data to process than in a census.
• What are the disadvantages of a sample?

  The disadvantages of samples are the data may not be as accurate and the sample may not be large enough to give information about small subgroups of the population.
• what does the size of the sample depend on?

  The size of the sample depends on the required accuracy and available resources. The larger the sample, the more accurate, but the more resources needed.
• What happens if the population is varied?

  If the population is varied you will need a larger sample that if the population was uniform.
• What can different samples lead to?

  Different samples can lead to different conclusions due to the natural variation in a population.
• What are sampling units?

  Individual units of a population are known as sampling units.
• What is a sampling frame?


  A sampling frame is a list of individually named or numbered sampling units of a population.
• What happens in random sampling?

  In random sampling, every member of the population has an equal chance of being selected. This sample should therefore be representative of the population. This also helps to remove bias from the sample.
• What are the three methods of random sampling?

  Simple random sampling, Systematic sampling and stratified sampling.
• What is a simple random sample of size n?

  A simple random sample of size n is one where every sample of size n has equal chance of being selected.
• How do you carry out a simple random sample?

  To carry out a simple random sample you need a sampling frame. Each person or thing is chosen at random.
• What are the two methods of choosing numbers for a simple random sample?

  Generating random numbers and lottery sampling
• How do you generate random numbers?

  Using a calculator, random number generator/computer or random number table.
• What is lottery sampling?

  In lottery sampling, the members of the sampling frame could be written on tickets and placed into a hat. The the required number of tickets is drawn.
• What happens in systematic sampling?

  In systematic sampling, the required elements are chosen at regular intervals from an ordered list. The first person should be picked at random via a random number generator and then the next should be taken from the regular intervals. Population size/ sampling size.
• What is stratified sampling?

  The population is divided into mutually exclusive strata and a random sample is taken from each. To work out the number sampled in a stratum = (no. in stratum/number in population) x overall sample size. Inside the stratum simple random sampling occurs.
• What is the formula for the number sampled in a stratum?

  The number sampled in a stratum = (number in a stratum/number in population) x overall sample size
• What are the advantages of simple random sampling?

  The advantages of simple random sampling are:

  • Free of bias
  • Easy and cheap to implement for small populations and small sample
  • Each sampling unit has a known and equal chance of selection
• What are the disadvantages of a simple random sample?

  The disadvantages of a simple random sample are:

  • Not suitable when the population size or the sample size is large.
  • A sampling frame is needed
• What are the advantages of systematic sampling?

  The advantages of systematic sampling are:

  • Simple and quick to use
  • Suitable for large samples and large populations
• What are the disadvantages of systematic sampling?

  The disadvantages of systematic sampling are:

  • A sampling frame is needed
  • It can introduce bias if the sampling frame is not random
• What are the advantages of stratified sampling?

  The advantages of stratified sampling are:

  • Sample accurately reflects the population structure
  • Guarantees proportional representation of groups within a population
• What are the disadvantages of stratified sampling?

  The disadvantages of stratified sampling:

  • Population must be clearly classified into distinct strata
  • Selection within each stratum suffers from the same disadvantages as simple random sampling.
• What are the two types of non-random sampling?


  The two types of non-random sampling are:

  • Quota sampling
  • Opportunity sampling
• What happens in quota sampling?

  In quota sampling, an interviewer or researcher selects a sample that reflects the characteristics of the whole population
• Describe the process of quota sampling

  The population is divided into groups according to a given characteristic. The size of each group determines the proportion of the sample that should have that characteristic. As an interviewer, you would meet people, assess their group and then, after interview, allocate them into the appropriate quota. This continues until all quotas have been filled. If a person refuses to be interviewed or the quota into which they fit is full, then you simply ignore them and move onto the next person.
• What is opportunity sampling?

  Opportunity sampling 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 for.
• What do you do in opportunity sampling?

  This could be the first 20 people you meet outside a supermarket on a Monday morning who are carrying shopping bags, for example.
• What are the advantages of quota sampling?

  The advantages of quota sampling are:

  • Allows a small sample to still be representative of the population
  • No sampling frame required
  • Quick, easy and inexpensive
  • Allows for easy comparison between different groups within a population
• What are the disadvantages of quota sampling?

  The disadvantages of quota sampling are:

  • 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 of opportunity sampling?

  The advantages of opportunity sampling are:

  • Easy to carry out
  • inexpensive
• What are the disadvantages of opportunity sampling?

  The disadvantages of opportunity sampling are:

  • Unlikely to provide a representative sample
  • Highly dependent on individual researcher
• What are quantitative variables and quantitative data?Give an example.

  Variables or data associated with numerical observations are called quantitative variables or quantitative data. An example is shoe size as you can give it a number.
• What are qualitative data or qualitative variables?Give an example

  Variables or data associated with non-numerical observations are called qualitative variables or qualitative data. An example of this is hair colour as you can not give it a number.