smarties sampling

Fieldwork skills

Learning Objectives

• ALL – to know different sampling methods

• MOST – reflect on advantages and disadvantages of sampling

• SOME – consider the effects of bias

Sampling

KWLR TABLEWhat I KNOW

about samplingWhat I WOULD

LIKE to know about sampling

What I have LEARNT about

sampling

The RANK order of what I have learnt today is

(the most important)

Complete the first two columns of your KWL

grid.

Learning Objectives




Why do we sample?1. it is quicker than

measuring every item

2. it is therefore much cheaper

3. often it is impossible to measure everything

4. it is unnecessary to measure everything

5. it is sometimes impossible to gain access to everythingLearning Objectives




The size of the sample will usually be dictated by the time and resources available. BUT the larger the sample the more likely it is to find a true picture of the data you are sampling.

Learning Objectives




Smarties samplingYou will be conducting a mini investigation to

practise sampling. You will be using smarties to demonstrate the different sampling techniques. Do not eat your smarties as you can’t carry out the investigation without them – make it to the end and then you can eat them!!

Stretch and challenge – for each type of sampling method you must attempt to write up your own definition of this technique.

Random samplingRandom sampling means that members of a 'population' have equal chances of being selected.To carry out this type of sampling, you will need to use a table of random numbers. Random numbers can also be generated using a calculator or computer.

Learning Objectives




Lay out your smarties in a row. Assign each smartie a number from 1- 20(we will deal with a population of

20 smarties).

A random number calculator will generate

numbers to identify which smarties will be part of the

random sample.

http://www.random.org/

Random sampling

Learning Objectives




Advantages DisadvantagesNo human bias involved in the selection process.

If the sample size is small we may by bad luck obtain an unrepresentative result





sampling



Learning Objectives




Add 3 things you have learnt

to your table

Systematic samplingSampling data at equal distances apart e.g. every fifty meters or every 10th person.

Learning Objectives




Lay out your smarties in a row. Assign each

smartie a number from 1- 20(we will

deal with a population of 20 smarties).

Take every 5th smartie – this will be your

systematic sample.

Systemaic sampling

Learning Objectives




Advantages DisadvantagesEnsures complete coverage of the sample area.

If the sample size is small we may by bad luck obtain an unrepresentative result

Stratified sampling'Strata' means 'layer'. A stratified sample is made up of different 'layers' of the population, for example, selecting samples from different age groups.

Learning Objectives




All the sweets are smarties but each smartie has a different colour and the colour represents a subjection of the

whole population. Select out all the red smarties these are the stratified sample.

Stratified sampling

Learning Objectives




Advantages DisadvantagesHelps to reduce bias because all sub groups of the population are included in the sample

Sometimes difficult to identify a sub group or strata





sampling



Learning Objectives




Add 3 things you have learnt

to your table

Test time

Learning Objectives




Q. Collecting sediment samples every 10m on a beachA. SystematicQ. In a beach questionnaire ensuring that participants both young and old are asked.A. StratifiedQ. Numbers are generated using a computer and these numbers are used as grid reference co ordinates for the site of studyA. RandomQ. In a sand dune investigation choosing a sample where there is a break of slope rather than at equally spaced intervalsA. Stratified

Avoiding bias

Learning Objectives




Select out your favourite colour smarties and eat them – this

would be a bias sample! Why?

Stretch and

Challenge

Where can I find out

more about this

topic?





sampling



Learning Objectives




Add 2-4 things you have learnt this lesson and

decide which is the most important thing you have

learnt or rank order everything you have

learnt from top to bottom.

smarties sampling

Education

random sampling

different sampling techniques

different sampling methodsto

sampling data

advantages disadvantages

effects of bias

sampling samplinglearnt

different colour