Collecting primary data in the field

Overview

Primary data, environmental quality survey and difference between closed and open questions in a questionnaire.

What you need to know

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Questions from this subtopic

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1. 1

   What is primary data, and how does it differ from secondary data?

   Model answer

   Primary data are collected at first hand by the investigator, in the field, for the specific purpose of that investigation - for example river depths you measured yourself, a pedestrian count you carried out, or completed questionnaires you administered. Secondary data already exist because someone else collected them, usually for a different purpose - census tables, Ordnance Survey maps, published river gauge records, newspaper reports. Primary data are exactly matched to your question and you know how accurate they are, but they are limited in quantity and cover only the time you were there. Secondary data give depth, longer time spans and wider coverage, but you did not control how they were gathered.

2. 2

   Why is it essential to decide exactly what you will measure before you go into the field?

   Model answer

   Because you usually only get one visit. Deciding the variables, the units, the number of sites, the number of repeats and the layout of the recording sheet in advance means every site is measured in the same way, so the results are comparable and can be processed statistically. Vague planning produces gaps, inconsistent units and data that cannot answer the question, and the mistake cannot be corrected once you have left the site.

3. 3

   What equipment would you use to measure a river channel and its flow, and what does each piece measure?

   Model answer

   A tape measure stretched from bank to bank at the water surface gives channel width. A metre rule or ranging pole held vertically at fixed intervals across that tape gives depth, from which mean depth and cross-sectional area are worked out. A flowmeter with an impeller, or a float and a stopwatch over a measured distance, gives velocity. A clinometer sighted between two ranging poles a known distance apart gives channel gradient. Callipers and a roundness index give the size and shape of the bedload, and a water sample or turbidity reading indicates the load carried in suspension.

4. 4

   How would you measure river velocity with a float and a stopwatch, and why is a flowmeter usually more accurate?

   Model answer

   Measure out a fixed length of channel, say ten metres, mark the start and the end, release a float just upstream of the start line so that it is already travelling at the speed of the water, and time it between the marks. Velocity is the distance divided by the time, and the run should be repeated several times and averaged. A flowmeter is usually more accurate because a float samples only surface velocity, which is faster than the average for the whole cross-section, and it is pushed by the wind and diverted by obstructions. A flowmeter can be held at a set depth at several points across the channel, giving a mean that reflects the whole flow.

5. 5

   How would you survey a beach profile, and what equipment does it need?

   Model answer

   Work along a transect running from the sea at right angles to the shoreline up to the back of the beach. Two ranging poles are placed at successive breaks of slope; the distance along the beach surface between them is measured with a tape, and the angle of that slope segment is read with a clinometer sighted from a mark on one pole to the same height mark on the other. The pair of readings is repeated for every segment, and the sequence of distances and angles is later plotted as a profile. Recording the state of the tide and the time is essential, because the length of beach exposed changes through the day.

6. 6

   What is an environmental quality survey, and how is one carried out?

   Model answer

   It is a structured way of scoring qualities of a place that cannot be measured with an instrument, such as building condition, litter, greenery, noise, traffic or the feeling of safety. The surveyor uses a bipolar scale, typically minus five to plus five or one to five, with a positive statement at one end and its opposite at the other, and scores each criterion at each site. The scores are totalled to give an index that can be mapped or compared between sites. It converts subjective impressions into numbers that can be processed and compared.

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