39 exam-style questions on Collecting and processing data — topic I2 of Skills in the study of ESS in the IB Environmental Systems and Societies syllabus — with answers and explanations. Samples below; the full set is free with an account.
A student records the percentage cover of five plant species at 2 m intervals along a 40 m transect running inland from a strandline. The most appropriate way to present these data is
Answer: a kite diagram showing each species as a band along the transect
A kite diagram keeps the position along the transect on one axis, so it shows both how abundant each species is and where along the gradient it drops out. Pie charts and whole-transect means throw away exactly the spatial information the survey was designed to collect.
At each of twelve points in a meadow a student measures soil moisture content and the total dry mass of the earthworms extracted from a pit of fixed volume. Both variables are continuous. To look for a relationship between them the data should be plotted as
Answer: a scatter graph with a line of best fit
Two continuous variables measured at the same sampling points call for a scatter graph, where each point is one site and the pattern of the cloud shows the relationship. Joining the points in collection order would imply a sequence that the sampling design does not contain.
Stream temperature is read from an analogue thermometer graduated in 1 °C divisions. The uncertainty that should be quoted in the column heading of the results table is
Answer: ± 0.5 °C, half of the smallest scale division
For an analogue scale the convention is half the smallest division, because that is the finest distinction the eye can defend when reading between two marks. A digital instrument is quoted differently, as plus or minus one unit in the last displayed digit.
A results table lists, for each of four sites, the mean nitrate concentration worked out from three repeat readings. These mean values are
Answer: processed data, because a calculation has been applied
Raw data are the readings exactly as taken from the instrument; anything derived from them by calculation, such as a mean, a percentage or a diversity index, counts as processed data. The two are tabulated separately so that a reader can check the processing step.
A student takes five repeat readings of nitrate concentration at one site. Four lie between 4.1 and 4.4 mg dm-3, while the fifth reads 19.6 mg dm-3. In the results table this fifth reading should be
Answer: recorded and marked as anomalous, then left out of the mean
Such a value stays in the raw data table and is flagged, never quietly deleted, because the reader has to be able to see what was excluded from the processing. Averaging it in would drag the site mean well above every reading the instrument actually settled on.
Eleven soil nitrate readings from one field include a single very high value taken beside a spill. Which measure of central tendency is least affected by that value?
Answer: The median of the eleven readings
The median depends only on the position of a value in the ordered set, so one extreme reading moves it by at most one place, while the mean is pulled directly towards it. Reporting the median alongside the mean is the standard way of showing that a distribution is skewed.
That was 6 of 39 Collecting and processing data questions.
Practise all 39 freeOutlineAO2 · 1–4 marks
A brief account or summary: the main points in two or three sentences, no evaluation.
StateAO1 · 1–2 marks
One word or one short sentence. No explanation, no working: the mark is for the fact itself.
DescribeAO2 · 1–4 marks
Give a detailed account of what it is or how it happens — steps, features, pattern — without saying why.
39 Collecting and processing data questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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