Population-And-Sampling Aqa Higher

Population & sampling

What are the different types of data?

• Primary data is data that has been collected by the person carrying out the research

  • This could be through questionnaires, surveys, experiments etc 

• Secondary data is data that has been collected previously

  • This could be found on the internet or through other research sources

• Qualitative data is data that is usually given in words not numbers to describe something

  • For example: the colour of a teacher’s car

• Quantitative data is data that is given using numbers which counts or measures something

  • For example: the number of pets that a student has

• Discrete data is quantitative data that needs to be counted

  • Discrete data can only take specific values from a set of (usually finite) values

  • For example: the number of times a coin is flipped until a ‘tails’ is obtained

• Continuous data is quantitative data that needs to be measured

  • Continuous data can take any value within a range of infinite values

  • For example: the height of a student

• Age can be discrete or continuous depending on the context or how it is defined

  • If you mean how many years old a person is then this is discrete

  • If you mean how long a person has been alive then this is continuous

What is a population?

• A population refers to the whole set of things which you are interested in

  • e.g. if a teacher wanted to know how long pupils in year 11 at their school spent revising each week then the population would be all the year 11 pupils at the school

• Population does not necessarily refer to a number of people or animals

  • e.g. if an IT expert wanted to investigate the speed of mobile phones then the population would be all the different makes and models of mobile phones in the world

What is a sample?

• A sample refers to a selected part (called a subset) of the population which is used to collect data from

  • e.g. for the teacher investigating year 11 revision times a sample would be a certain number of pupils from year 11

• A random sample is where every item in the population has an equal chance of being selected

  • e.g. every pupil in year 11 would have the same chance of being selected for the teacher’s sample

• A biased sample is where the sample is not random

  • e.g. the teacher asks pupils from just one class

What are the advantages and disadvantages of using a population?

• You may see or hear the word census – this is when data is collected from every member of the whole population

• The advantages of using a population

  • Accurate results – as every member/item of the population is used

    • In reality it would be close to every member for practical reasons

  • All options/opinions/responses will be included in the results

• The disadvantages of using a population

  • Time consuming to collect the data

  • Expensive due to the large numbers involved

  • Large amounts of data to organise and analyse

What are the advantages and disadvantages of using a sample? 

• The advantages of using a sample

  • Quicker to collect the data

  • Cheaper as not so much work involved

  • Less data to organise and analyse

• The disadvantages of using a sample

  • A small sample size can lead to unreliable results

    • Sampling methods can usually be improved by taking a larger sample size

  • A sample can introduce bias

    • particularly if the sample is not random

  • A sample might not be representative of the population

    • Only a selection of options/opinions/responses might be accounted for 

    • The members/items used in the sample may all have similar responses
      e.g. even with a random sample it may be possible the teacher happens to select pupils for his sample who all happen to do very little revision

• It is important to recognise that different samples (from the same population) may produce different results