CSCA common mistakes
CSCA · Understand the traps and how to avoid them.
When a question describes a stockout and high inventory simultaneously, candidates blame a single forecasting error instead of separating the replenishment lead-time mismatch from the forecast bias, and pick whichever answer mentions 'better forecasting'.
Forecasting is the most familiar lever, so it becomes the default explanation for any inventory problem. The exam deliberately writes scenarios where the root cause is a lead-time or lot-sizing mismatch, and the forecast-error answer is the distractor.
What to do instead
Before choosing, classify the symptom: is inventory too high, too low, or both at different SKUs? Map it to forecast bias (systematic), forecast error (random), lead-time variability, or order batching. If the stem shows both excess and shortage across items, the answer is almost never 'improve forecast accuracy' alone.
Candidates compute a reorder point using average demand only, ignoring the safety stock term, or add safety stock but forget to include lead time in the demand-during-lead-time calculation.
The formula ROP = demand during lead time + safety stock is known, but under time pressure candidates collapse it to 'average daily demand x lead time' and treat that as the answer.
What to do instead
Write the structure explicitly every time: ROP = (average demand per period x lead time in periods) + z x standard deviation of demand during lead time. Check whether the stem gives daily or weekly demand and whether lead time is in the same unit, then confirm the safety stock term appears in the answer.
Candidates treat a high service level target as a cost-free improvement and select answers that raise service level without addressing the inventory or cost trade-off the question asks about.
Service level sounds like an unqualified good, and questions that ask 'what should the planner do to improve fill rate' tempt answers like 'increase safety stock' even when the stem states a working-capital constraint.
What to do instead
Read the constraint clause in the stem first (budget, space, cash, capacity). Any option that improves service level by adding inventory must be tested against that constraint. Prefer options that reduce variability, shorten lead time, or segment inventory by criticality, since these raise service without proportional inventory growth.
Candidates classify every item as class A in ABC analysis, or apply ABC by unit volume rather than by annual consumption value, and then choose a stocking policy inconsistent with the classification.
The Pareto idea is remembered loosely, and candidates equate 'important' with 'high quantity' instead of 'high value x volume'.
What to do instead
Compute annual usage value (unit cost x annual quantity) before classifying. Then match policy to class: tight control and frequent review for A, automated reorder rules for B, periodic review and higher safety stock tolerance for C. If the stem gives only unit counts, flag that value data is missing rather than assuming A.
Candidates pick a supplier-selection answer based on lowest quoted price when the stem describes quality defects, long lead times, or compliance requirements.
Price is the most visible and comparable number, so it anchors the choice even when total cost of ownership is what the question is testing.
What to do instead
Convert each option to total cost of ownership: price plus freight, duty, inspection, defect and rework cost, inventory carrying cost of longer lead times, and risk of disruption. When the stem mentions quality or delivery problems, price-led answers are usually the distractor.
Candidates answer contract-type questions by matching the contract name to the situation without checking who bears the cost risk, and so choose a fixed-price contract for a scope that is genuinely uncertain.
Contract names are memorized as definitions, but exam items test risk allocation: fixed-price shifts cost risk to the supplier, cost-reimbursable keeps it with the buyer, and incentive contracts share it.
What to do instead
For each contract option, state in one line who absorbs overrun risk. Then check the stem for scope clarity and duration. Well-defined short scope favors fixed price; uncertain or long development scope favors cost-reimbursable or incentive arrangements.
Candidates treat a logistics cost question as a pure transport-rate comparison and ignore the inventory carrying cost and customer service effect of the mode or consolidation choice.
Freight rates are concrete, while carrying cost and service impact are implied, so the cheaper mode looks correct even when total landed cost is higher.
What to do instead
Build a two-line comparison: transport cost and inventory-plus-service cost. Faster, more expensive modes reduce pipeline inventory and safety stock; slower modes raise them. Choose the option with the lower total, and if the stem gives no holding-cost data, say so rather than defaulting to the cheapest rate.
Candidates answer lean questions by removing inventory everywhere, including buffers that protect a constraint or absorb demand variability, and select 'reduce WIP to zero' style options.
Lean is summarized as waste elimination, and inventory is taught as waste, so candidates over-apply the principle and miss the distinction between waste and necessary buffer.
What to do instead
Separate the seven wastes from protective buffers. Ask whether the inventory in the stem protects a bottleneck, a long replenishment lead time, or demand variability. Lean removes buffers by first reducing the variability or lead time that justified them, so answers that cut inventory without that precondition are wrong.
Candidates confuse the purpose of control charts and process capability indices, using Cp or Cpk to detect whether a process is in control, or using a control chart to judge specification compliance.
Both are statistical process tools and appear in the same chapters, so their distinct roles blur under exam pressure.
What to do instead
Fix the roles: control charts detect the presence of special-cause variation over time; Cp and Cpk compare process spread and centering to specification limits. If the question asks 'is the process stable', the answer is a control chart. If it asks 'can the process meet the spec', the answer is a capability index.
Candidates compute Cpk with the process standard deviation but use the specification width instead of the nearer specification limit, or report Cp when the process is off-center.
Cp = (USL - LSL) / 6 sigma is the simpler formula and gets reused for Cpk, which produces an inflated value and the wrong conclusion about centering.
What to do instead
Always take the minimum of the two one-sided ratios: Cpk = min[(USL - mean) / 3 sigma, (mean - LSL) / 3 sigma]. If mean is not centered, Cpk is lower than Cp; if the stem shows an off-center process, the answer must reflect that gap.
Candidates treat Six Sigma DMAIC and lean tools as interchangeable, proposing a kaizen event or 5S for a problem that is actually a variation problem needing measurement and root-cause analysis, or vice versa.
Both fall under continuous improvement, and the tool names are learned as a list rather than matched to problem type.
What to do instead
Diagnose the problem type first. Flow, waiting, and travel problems call for lean tools (value stream mapping, 5S, standard work). Defect, variation, and yield problems call for DMAIC with measurement system analysis and designed experiments. Match the tool to the diagnosed problem, not to the improvement vocabulary in the stem.
Candidates select the answer that optimizes a single function, such as minimizing procurement cost or maximizing manufacturing utilization, when the stem describes a cross-functional conflict.
Exam items are written around functional silos, and each option sounds locally optimal. The correct answer usually requires recognizing that local optimization raises total supply chain cost.
What to do instead
When the stem shows a conflict between functions, evaluate each option on total supply chain cost and end-customer service, not the metric of the function named. Options that improve one department's metric while increasing inventory, expediting, or lost sales elsewhere are distractors.