Sampling and Methods
Collecting fieldwork data fairly: random, systematic and stratified sampling, primary against secondary data, and how to justify the method so the results are fair and representative.
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Free interactive practice at using the material, which is what the marks are for.
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Collecting the data
Once an enquiry has its question, the next strand is collecting data, and you can rarely measure everything, so you take a sample. How you sample matters, because a poor sample gives a biased, misleading result. There are three main methods. Random sampling gives every point an equal chance, often using random numbers, which avoids bias. Systematic sampling takes readings at regular intervals, such as every ten metres, giving even coverage. Stratified sampling splits the sample so it matches the groups in the population, such as different age groups. You also decide between primary data, which you collect yourself, and secondary data, gathered by others. The key skill is not just naming a method but justifying why it suits your enquiry. This module covers sampling and data collection.
Sampling words
Learn these before you match any method, and remember the aim is fair, representative data.
Random against systematic
Two of the sampling methods are easy to mix up, so it helps to weigh them side by side.
How to choose and justify a method
Never just name a sampling method. Match it to the enquiry, then say why. Ask what would make the data fair and stop it being biased toward one spot or group. If you need every location to have a fair chance, reach for chance-based selection. If you want even coverage along a line, take readings at steady intervals. If different groups must be reflected, split the sample to match them. Then state plainly why that choice gives results that represent the whole area.
Match the method to how it works
- random sampling
- systematic sampling
- stratified sampling
- primary data
- points chosen by chance, such as with random numbers
- readings taken at regular fixed intervals
- the sample split to match groups in the population
- data the student collects first hand
Which sampling method is this?
A student measures the depth of a river every ten metres along a straight transect. Which sampling method is being used?
- Systematic sampling.
- Random sampling.
- Stratified sampling.
- Collecting secondary data.
Good data collection
Select the TWO things that make fieldwork data collection sound.
- Justify why the sampling method suits the enquiry
- Measure and record results carefully and accurately
- Only measure where the site looks interesting
- Make up readings to save time
Total readings
A student collects data at 4 sites and takes 5 readings at each site. Multiply to find the total number of readings collected.
Order collecting the data
Put the steps of collecting fieldwork data in order, earliest first.
- Decide what needs to be measured
- Choose a suitable sampling method
- Measure and record the data in the field
- Check the data is complete and accurate
Complete the facts
Collecting data from a selection rather than from everything is called _____. Choosing points by chance so each has an equal chance is _____ sampling. Taking readings at regular intervals is _____ sampling. Splitting the sample to match groups in the population is _____ sampling.
Match the aim to the best method
- giving every spot an equal chance
- getting even coverage along a river
- reflecting different age groups fairly
- gathering figures from a government website
- use random sampling
- use systematic sampling
- use stratified sampling
- use secondary data
Spot the true sampling facts
Tap the TWO statements that are true about sampling.
- Random sampling gives every point an equal chance
- A good answer justifies why a sampling method was chosen
- Sampling only the interesting spots avoids bias
- Making up data is a sound method
Choose the sampling
Read each case and choose the best method, with a reason.
- A student wants pebble sizes measured evenly all the way along a beach. Which sampling method fits best?
- A student wants a survey to reflect the different age groups of shoppers in a town. Which method fits best?
- A student names systematic sampling but never says why they used it. How should the answer improve?
Justify your sampling
A student is planning how to collect data for a river enquiry. Explain the sampling methods available and justify a suitable choice.
- Explain what sampling is and why it is needed
- Describe random and systematic sampling
- Describe stratified sampling and when it helps
- Recommend and justify a method for measuring the river fairly
- Finish with a judgement on how the choice keeps the data fair and representative