Junior Economist Qualification common mistakes
Junior Economist Qualification · Understand the traps and how to avoid them.
In elasticity questions, computing the ratio of absolute changes (ΔQ/ΔP) and reporting that as the price elasticity of demand instead of using percentage changes or the point formula (dQ/dP)·(P/Q).
Everyday language treats 'responsiveness' as a slope, and textbooks often draw linear demand curves, so candidates conflate slope with elasticity. The units of ΔQ and ΔP differ, so the raw ratio is unit-dependent and meaningless as an elasticity.
What to do instead
Before calculating, write down which elasticity is asked for (own-price, income, cross-price) and apply the matching formula. For arc elasticity use the midpoint base: ((Q2−Q1)/((Q1+Q2)/2)) ÷ ((P2−P1)/((P1+P2)/2)). Sanity-check the sign: own-price demand elasticity must be negative, income elasticity positive for normal goods, cross-price positive for substitutes.
Treating accounting profit as economic profit, or omitting implicit costs and the opportunity cost of owner capital and labour when judging whether a firm should stay in business in the short run versus the long run.
Candidates carry over the business-accounting convention that profit equals revenue minus explicit cash outlays, and exam vignettes deliberately supply only explicit cost figures to test whether implicit costs are recognised.
What to do instead
Build a two-column cost table: explicit costs and implicit costs (foregone salary, foregone rent on owned premises, normal return on equity). Compare price with AVC for the shutdown decision and with ATC (including normal profit) for the long-run exit decision. State explicitly which cost concept each number represents.
Confusing a movement along the aggregate demand or aggregate supply curve with a shift of the curve, and then mixing up demand-pull and cost-push inflation when explaining an observed price-level and output change.
Micro-level supply-and-demand diagrams are drilled heavily, so candidates transfer the vocabulary loosely to the AD–AS model, where the axes are the price level and real output and the shifters are different (money supply, expectations, productivity, input prices).
What to do instead
Memorise the shifter lists separately for each model. For any AD–AS scenario, first identify which curve shifted and why, then read off the joint movement in the price level and real output: price level up with output up implies demand-pull; price level up with output down implies a negative supply shock. Draw the before-and-after diagram even when the question is verbal.
Reporting a computed statistic (mean, growth rate, correlation, regression coefficient) without checking whether the underlying series is nominal or real, seasonally adjusted, or expressed in the same units and base year as the comparison series.
Exam data tables are presented as raw numbers, and candidates focus on the arithmetic. Nominal-versus-real and base-year mismatches are the most common planted trap because they are invisible unless you look at the table header.
What to do instead
Before computing anything, read every column header for units, currency, base year, and seasonal adjustment, and write a one-line 'data audit' note. Deflate nominal values with the stated price index before comparing across years. If units differ between series, convert first and show the conversion factor in your working.
Interpreting a regression coefficient as a causal effect, or interpreting an R-squared as evidence that the model is correctly specified or that the relationship is causal.
Software output presents coefficients and R-squared side by side with no warning labels, and candidates are trained to report what the output shows. Omitted-variable bias, simultaneity, and measurement error are not visible in the output.
What to do instead
For every coefficient, state the identifying assumption (conditional independence, no simultaneity, no measurement error) and say what would violate it. Treat R-squared as a goodness-of-fit measure only; high R-squared with biased coefficients is common in time-series data with trends. When asked for a causal claim, name the design (randomisation, instrumental variable, difference-in-differences, regression discontinuity) that would support it.
Reading a p-value as the probability that the null hypothesis is true, or as the probability the result will replicate, and then drawing a policy conclusion from a single borderline significance test.
The p-value is defined as the probability of data at least as extreme as observed, conditional on the null being true - the reverse conditional. Candidates also over-weight the 5% threshold as a bright line and ignore effect size and confidence-interval width.
What to do instead
State the definition explicitly in the answer: p = P(data at least this extreme | H0 true). Report the confidence interval and the economic magnitude of the effect alongside the p-value. Treat results near the threshold as inconclusive rather than decisive, and note that statistical significance is not economic significance.
Mixing up average and marginal tax rates, or applying the statutory rate to the whole base instead of using the bracket structure, when computing an effective tax rate or a progressivity measure.
Headline rates are widely quoted in the media and candidates default to multiplying income by the top rate, which overstates liability and distorts any progressivity conclusion. The distinction between statutory incidence and economic incidence is also frequently skipped.
What to do instead
Compute liability bracket by bracket, then derive average rate (tax ÷ income) and marginal rate (tax on the next unit) separately and label both. For incidence questions, state the statutory payer, then apply the elasticity rule: the less elastic side bears more of the burden regardless of who remits the tax.
Confusing the money multiplier with the deposit multiplier, or assuming the central bank directly sets the money supply and the quantity of reserves, when analysing how an open-market operation or a change in the reserve requirement affects the money stock.
Textbook treatments present a simple deposit multiplier (1/rr) as if it were the money multiplier, and candidates then ignore currency holdings, excess reserves, and the fact that modern central banks target an interest rate and accommodate reserve demand.
What to do instead
Write the money multiplier as (1 + c)/(rr + e + c) with currency ratio c, reserve requirement rr, and excess reserve ratio e, and explain how each term moves it. For policy questions, state the operating target (interest rate versus reserve quantity) first, then trace the effect through reserves, the multiplier, and broad money, noting that the multiplier is not a policy lever.
Analysing a tariff or quota using only the domestic price effect and ignoring the terms-of-trade effect, the deadweight loss triangles, and the distinction between nominal and effective protection.
Candidates memorise 'tariffs raise domestic prices and reduce imports' and stop there, because the welfare decomposition requires drawing the partial-equilibrium diagram with the world price line and identifying consumer loss, producer gain, government revenue, and efficiency loss.
What to do instead
Draw the small-country diagram and label all five areas: consumer surplus loss, producer surplus gain, tariff revenue, production distortion loss, and consumption distortion loss. For a large country, add the terms-of-trade gain rectangle and compare it with the two triangles to determine the optimal tariff. For effective protection, use (t − a·t_input)/(1 − a) and state the input share a.
Answering ethics and professional-conduct questions by describing what a 'reasonable person would do' rather than applying the specified framework: identifying the conflict of interest, the duty owed, the disclosure obligation, and the escalation path in that order.
Ethics questions look like common-sense judgement calls, so candidates give intuitive answers and skip the structured analysis that the marking scheme rewards. They also overlook that a conflict can exist without any improper act.
What to do instead
Use a fixed four-step template for every ethics item: (1) identify the parties and the duty owed to each; (2) identify the actual, potential, or perceived conflict; (3) state the required action - disclose, recuse, obtain consent, or decline; (4) state the escalation path if the issue is unresolved. Cite the specific principle (integrity, objectivity, confidentiality, competence) rather than general fairness language.