38 exam-style questions on Concluding and evaluating — topic I3 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 group compares mean species richness in grazed plots (mean 8.2 species, range 5-11) with ungrazed plots (mean 9.1 species, range 4-13). Which conclusion is best supported by these data?
Answer: The means differ by less than the spread within each treatment.
The 0.9-species gap between the means is dwarfed by ranges of 6 and 9 species, so the data cannot separate the two treatments. Claiming a significant difference also implies a statistical test that was never carried out, and claiming no effect asserts more certainty than the sample allows.
A dissolved oxygen meter was never calibrated and reads 0.5 mg dm-3 above the true value in every sample taken during a river study. This is best described as
Answer: a systematic error, which repeating the readings would not reduce
A systematic error shifts every reading in the same direction by a similar amount, so the mean stays wrong however many repeats are taken and only recalibration against a standard removes it. Random error scatters readings either side of the true value and is averaged out by repeats.
Three repeats of a soil infiltration measurement agree to within 2 %, but the infiltrometer ring was pushed only 1 cm into the soil so water escaped sideways. The data are therefore
Answer: reliable but not valid
Close agreement between repeats demonstrates reliability, but a method that measures the wrong quantity gives values that are consistently wrong, so validity fails. Reliability is about repeatability; validity is about whether the measurement actually answers the research question.
In a capture-mark-recapture study of a beetle population, some paint marks wore off between the first and second sampling. The estimated population size will be
Answer: overestimated, because fewer marked individuals are recaptured
In the Lincoln index N = (n1 x n2) / n3, the number of marked individuals recaptured sits in the denominator, so lost marks lower n3 and inflate N. A creditworthy evaluation names the limitation and the direction in which it biases the result.
A student's report ends: 'The same transect should be resurveyed after the new sea wall is built, to see whether the zonation pattern shifts.' In an ESS evaluation this sentence is
Answer: an extension, because it asks a new research question
Improvements repair the method that was used, such as adding replicates or calibrating an instrument; extensions keep the method and take the enquiry in a new direction. Presenting one as the other is the commonest error in the evaluation section of an IA.
A student's method produces closely agreeing results every time it is repeated, but the quantity it measures does not answer the research question that was set. The results are best described as
Answer: reliable but not valid
Reliability is about agreement between repeats; validity is about whether the measurement answers the question. The pair is worth separating because repeating a well-controlled method more times improves reliability and does nothing whatever for validity.
That was 6 of 38 Concluding and evaluating questions.
Practise all 38 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.
DistinguishAO2 · 1–4 marks
Make the difference clear for BOTH terms — a definition of one of them is only half an answer.
38 Concluding and evaluating questions — free with an account. Spaced repetition, streaks and full exam simulations included.
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