Sampling and Methods

A method is a claim

You cannot measure everything, so you measure some of it and argue that the some stands for the whole. That argument is what a sampling method is, and it is why the examiner asks you to justify the one you chose rather than to name it. The same is true at the other end of the enquiry. When you pick a graph you are deciding what the reader will compare, so a presentation method is a claim as well. A line graph says the points belong on a continuum. A bar chart says they are separate categories. A scatter graph says two things might be related. Choose the wrong one and you have argued something you did not mean to. So both halves of this module are justified the same way: say what the choice lets you see, and say what it hides. That second half is the one candidates leave out, and it is where the marks are. A method with no stated weakness reads as a method that was never really chosen. This matters more on Paper 3 than anywhere else. Section B is worth 39 of the 76 marks on the paper, and it examines both an unfamiliar fieldwork scenario and your own two enquiries, which the specification requires to be in contrasting environments, to cover physical and human geography with at least one showing how the two interact, and to be carried out on at least two occasions outside the classroom.

Six terms, each with the way it fails

Learn the weakness alongside the definition. The weakness is the half that earns the marks, and each of these has a different one.

Designing a data collection plan

Six decisions, and the order matters because each one constrains the next. Put them in sequence.

• Settle the question, so you know what would count as an answer
• Decide what has to be measured for that question to be answerable
• Choose where and when to measure it, and how many sites you need
• Choose the sampling technique, and write down why that one suits this population
• Design the recording sheet before leaving, so nothing is written on the back of a hand
• Try it at one site first, then fix what did not work before collecting the rest

Why justify rather than describe?

A candidate writes that they used systematic sampling at 10 m intervals along a transect. The answer is accurate and gains few marks. Why?

• Because describing what you did is not the same as arguing that it was appropriate. A justification says why this technique suits this population, what it makes visible, and what it risks missing, such as an interval that could coincide with a repeating feature. The examiner is testing whether the method was chosen or simply carried out.
• Because systematic sampling is the weakest of the three techniques.
• Because the answer needs more detail about the equipment used.
• Because the answer is too short to reach the higher mark bands.

Choosing, measuring, showing

Three sets of decisions, one rule running through all of them: state what the choice makes visible and what it puts out of reach.

Match each finding to the way of showing it

Say what it hides

The examiner reports on this section say the same thing every year: candidates describe their methods accurately and never argue for them. The fix is one sentence per choice, and it has two halves. What does this method let me see, and what does it put out of reach? Both halves earn. The first shows you understood the purpose; the second shows you understood the limits, and a candidate who can name a specific weakness of their own method is demonstrating something a textbook definition cannot. Notice that the weakness must be specific to the method and the place. "It might not be fully accurate" could be written under any method ever used and therefore earns nothing, whereas "sampling every tenth property risked coinciding with the corner shops on that street" could only be written by somebody who thought about that street. The same sentence works for presentation. A line graph across separate categories claims a continuity that is not there; a pie chart of nine slices claims proportions the eye cannot compare. Saying why you rejected the obvious alternative is one of the cheapest marks in the section. Two habits. Repeat anything variable and say that you did, because one reading is a moment and three averaged is a measurement. And know your own enquiries precisely, since this section asks about them directly, which nothing else in the qualification does: the title, the location, the date, the method, the sample size and what you found.

Complete the fieldwork method facts

Section B of Paper 3 carries _____ marks of the 76 available, and it asks about an unfamiliar scenario as well as about the two enquiries you carried out yourself. Taking readings every 10 m along a transect of 100 m gives _____ sites once both ends are counted. A bipolar survey usually scores each pair of opposites from minus 3 to plus _____. A rank correlation returns a value between minus 1 and plus 1, and needs roughly _____ pairs of data before the result carries any weight. The one technique that guarantees every group appears in proportion to its size is _____ sampling.

Spot the three sound method statements

Select the THREE statements that could stand as they are in an answer.

• Taking every tenth property risked coinciding with a repeating feature of that street, so the interval was checked against the frontages before collection began.
• Velocity was timed three times at each site and averaged, because a single float run records one moment rather than a representative speed.
• A scatter graph was chosen because it can show that two variables are unrelated as well as that they are, which a bar chart cannot.
• The method may not have been fully accurate, so the results should be treated with some caution.
• Random sampling was used because it is the most reliable of the three techniques.
• The rank correlation returned a strong positive value, which proves that one variable caused the other.

A 6-mark justification, marked

Justify the sampling method used in one of your fieldwork enquiries. [6 marks] In our human enquiry on how environmental quality changed with distance from the town centre, we used systematic sampling, taking readings every 200 m along a single transect running outwards from the market square, which gave us nine sites. The technique suited the question because the question was about change with distance: a transect places the sites in order along the gradient we were testing, and a fixed interval means the gaps between readings are equal, so any change we found could be attributed to distance rather than to where we happened to stop. It is also simple to describe and another group could repeat it exactly, which random coordinates would not allow. It does hide things, and two of them mattered. A fixed interval can coincide with a repeating feature, so before collecting we walked the route and checked that our 200 m points did not all fall on main road junctions, which would have surveyed junctions rather than the town. And a single transect describes one line out of the centre rather than the town as a whole, so our conclusion is about that route. Stratified sampling would have covered the different types of area in proportion, but it needs the make-up of the town known in advance and we did not have that before the visit. We also scored each site from minus 3 to plus 3 on six paired opposites, and all three of us scored independently and averaged, because a bipolar score is a judgement and one person's judgement is not evidence. What earned the marks: the method matched to the question rather than praised in general; the interval and the sample size stated; a weakness specific to that route rather than a general caution; the rejected alternative named with the reason it was not available; and a second method justified in one sentence on the same pattern.

Find the two that would cost marks

Five sentences from answers about fieldwork methods. Two would lose credit for how they argue rather than for being factually wrong. Tap those TWO.

• There may have been some inaccuracy in our results, so they should be treated with caution.
• We checked that our fixed interval did not land on the same kind of frontage each time, which would have described one type of property rather than the street.
• The strong positive correlation proves that higher footfall caused the higher rents we recorded.
• Each reading was taken three times and averaged, since one measurement records a moment rather than a typical value.
• Stratified sampling was ruled out because we had no breakdown of the area before we arrived.

Build the justification sentence

Assemble a sentence that argues for a method instead of describing it.

Four decisions in the field

Each is a real choice made before or during collection. Pick the response that would earn most in an answer about it.

• You are surveying a wood and know nothing about how the tree species are distributed within it.
• You plan to survey every tenth house along a street and notice on the walk out that every tenth frontage is a corner property.
• You have pedestrian counts and rent levels for fifteen sites and want to show whether they are connected.
• Your group is scoring environmental quality from minus 3 to plus 3 at each site.

Justify your methods

For one of your fieldwork enquiries, justify the method you used to collect your data and the method you used to present it. [9 marks]

• This section asks about your own work directly
• What the method made visible, not what you did
• A site-specific weakness, not a general caution that would fit any method anywhere
• The rejected alternative is among the cheapest marks in the section
• A graph is a claim about what the reader should compare