Operations Management and Strategic Management · Designing of Operational Systems and Control

Quality Control and Quality Management for CMA Inter

Updated 10 October 2026 · Fact-checked

Quality control checks products against standards and corrects defects. Quality management is wider: it plans, assures and improves quality across the whole organisation using tools like control charts, TQM, Six Sigma, Kaizen and quality circles. To solve questions, define the term, apply the tool or formula, then interpret the result.

Understand Quality Control and Quality Management

Quality means fitness for use: a product or service meets the customer's stated and implied needs. A product can be well made but still poor quality if it does not suit the customer.

Quality control (QC) is a reactive, product-focused activity. You inspect output, compare it with a standard and act on the gap. Quality assurance (QA) is a preventive, process-focused activity. It builds systems and procedures so that defects do not occur. Quality management covers planning, control, assurance and improvement together.

Statistical quality control (SQC) uses sampling and statistics instead of checking every item. It has two parts. Acceptance sampling decides whether to accept or reject a lot based on a sample. Process control uses control charts to see whether a process is stable. Variation due to chance causes is natural. Variation due to assignable causes (a worn tool, a wrong material) needs action. A point outside the control limits, or a clear pattern, signals an assignable cause.

Control charts are of two kinds. Variable charts (X-bar and R charts) track measured values such as length or weight. Attribute charts (p chart, c chart, np chart) track counts such as defectives or defects. A p chart uses the proportion of defective items. A c chart uses the number of defects per unit.

Total Quality Management (TQM) makes quality everyone's job, aimed at customer satisfaction and continuous improvement. Its main principles are customer focus, total employee involvement, process approach, continuous improvement, fact-based decisions and supplier partnership. Six Sigma is a data-driven method to cut defects to about 3.4 per million opportunities, using the DMAIC cycle: Define, Measure, Analyse, Improve, Control. Kaizen means small, continuous improvements by everyone. A quality circle is a small voluntary group of employees from the same work area who meet regularly to solve work problems.

Key rules to remember

Control limits for X-bar chart: UCL = X̿ + A₂R̄ ; LCL = X̿ − A₂R̄; X̿ is the grand mean of sample means and R̄ the mean range. A₂ is given in the question's table for the sample size.
Control limits for R chart: UCL = D₄R̄ ; LCL = D₃R̄; D₃ and D₄ depend on sample size and are supplied in the question. Do not use memory.
Fraction defective (p): p = Number of defectives ÷ Number inspected; p̄ = total defectives ÷ total items inspected across all samples.
p chart control limits: p̄ ± 3 × √[p̄(1 − p̄) ÷ n]; n is the sample size. If the lower limit is negative, take it as zero.
c chart control limits: c̄ ± 3 × √c̄; c̄ is the average number of defects per unit. A negative lower limit is taken as zero.
Six Sigma target: About 3.4 defects per million opportunities (DPMO); DPMO = (Defects ÷ (Units × Opportunities per unit)) × 10,00,000.
DMAIC cycle: Define → Measure → Analyse → Improve → Control; Keep the order. It is a common one-line question.

How to solve Quality Control and Quality Management questions

Quality questions are either theory (explain, differentiate, discuss) or numerical (control limits). Use the method that fits.

1Read the verb. 'Differentiate' needs a point-wise comparison; 'explain' needs definition plus features; 'compute' needs a calculation.
2For theory, open with a one-line definition in your own words.
3Give 4 to 6 clear points: features, principles, steps or merits, each with a short explanation.
4Add a brief Indian example, such as an auto-parts maker or a food-processing plant, to show application.
5For numerical questions, write the formula first, then list the values given, including any table constants.
6Compute the centre line and the upper and lower limits. Set a negative lower limit to zero.
7Compare each sample point with the limits and state whether the process is in control.
8Close with a one-line interpretation and the action to take, such as finding the assignable cause.

Quickest way: Two-minute approach for quality MCQs and short answers

When to use it: Use it for the 2-mark MCQs and for short-note questions when time is short.

Match the keyword to the concept: 'prevention' or 'process' means QA; 'detection' or 'inspection' means QC.
'Defects per million' points to Six Sigma. 'Small continuous change' points to Kaizen. 'Voluntary small group' points to a quality circle.
'Measured data' points to X-bar and R charts. 'Count of defectives' points to p chart. 'Count of defects per unit' points to c chart.
For limit calculations, use mean ± 3 standard errors for attribute charts and the given table constants for X-bar and R charts.
Check that only one option fits. There is no negative marking, so always attempt every MCQ.

Common mistakes in Quality Control and Quality Management

Treating quality control and quality assurance as the same thing
Both words sound alike and both deal with defects.
Fix: Remember: QC detects and corrects defects in the product; QA prevents defects by fixing the process.
Confusing a p chart with a c chart
Both are attribute charts and both use 3-sigma limits.
Fix: p chart is for the proportion of defective items in a sample. c chart is for the count of defects in one unit or area.
Leaving a negative lower control limit in the answer
Students apply the formula mechanically.
Fix: A proportion or count cannot be negative. Write the lower limit as zero.
Using the wrong sample size in the p chart limits
Students use the total items inspected instead of the size of each sample.
Fix: Use n as the size of one sample. Use the total only to find p̄.
Writing Six Sigma as '6 per cent defects' or mixing up DMAIC order
Students memorise the name but not the meaning.
Fix: Write 3.4 defects per million opportunities and the order Define, Measure, Analyse, Improve, Control.
Saying a point inside the limits always means the process is perfect
Students ignore patterns such as a long run on one side of the centre line.
Fix: State that points within limits show the process is in statistical control, not that output meets customer specifications. Mention checking for patterns.

Worked examples

Example 1

A factory inspects 5 samples of 200 items each. The numbers of defective items are 8, 12, 10, 6 and 14. Compute the control limits for a p chart and state whether the process is in control.

Show the solution

Total defectives = 8 + 12 + 10 + 6 + 14 = 50.
Total inspected = 5 × 200 = 1,000.
p̄ = 50 ÷ 1,000 = 0.05.
Standard error = √[0.05 × 0.95 ÷ 200] = √(0.0475 ÷ 200) = √0.0002375 ≈ 0.01541.
3 × standard error ≈ 0.04623.
UCL = 0.05 + 0.04623 = 0.0962 (about 9.62%).
LCL = 0.05 − 0.04623 = 0.0038 (about 0.38%).
Sample fractions: 8/200 = 0.04; 12/200 = 0.06; 10/200 = 0.05; 6/200 = 0.03; 14/200 = 0.07.
All values lie between 0.0038 and 0.0962.

Answer: p̄ = 0.05, UCL ≈ 0.0962, LCL ≈ 0.0038. All five samples fall within the limits, so the process is in statistical control.

Example 2

Differentiate between quality control and quality assurance, and state the principles of TQM.

Show the solution

Start with the meaning: QC is the set of operational checks that find and correct defects in output. QA is the set of planned systems that prevent defects.
Compare on nature: QC is reactive and corrective; QA is proactive and preventive.
Compare on focus: QC focuses on the product; QA focuses on the process and system.
Compare on timing: QC is done after or during production; QA is done before and throughout production.
Compare on responsibility: QC is usually with the inspection or quality team; QA involves the whole organisation.
Compare on tools: QC uses inspection, testing and control charts; QA uses audits, documented procedures and training.
TQM principles: customer focus; total employee involvement; process approach; continuous improvement (Kaizen); decisions based on facts and data; supplier partnership; strong leadership commitment.

Answer: QC detects and corrects defects in the product, while QA prevents defects by building a sound process. TQM rests on customer focus, employee involvement, process approach, continuous improvement, fact-based decisions, supplier partnership and leadership commitment.

Exam tips

Write differences in a two-column table style using clear points, but keep each point short. Aim for at least five points.
For control chart sums, show the formula, the values and the limits. Step marks are given even if the final figure is slightly off.
Always end a numerical answer with a one-line interpretation: in control or out of control, and the action.
Link TQM with Kaizen, Six Sigma and quality circles in one answer. Examiners like a connected view of improvement tools.
Practise the MCQ keywords: DPMO, DMAIC, assignable cause, p chart, c chart, quality circle.

Practice questions from Designing of Operational Systems and Control

Quality Control and Quality Management in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Quality Control and Quality Management: frequently asked questions

What is the main difference between quality control and quality assurance?

Quality control finds and corrects defects in finished or in-process products. Quality assurance prevents defects by designing and following good processes. QC is product-oriented and reactive, while QA is process-oriented and preventive.

What are the key principles of TQM for CMA Intermediate?

Customer focus, total employee involvement, process approach, continuous improvement, decisions based on facts and supplier partnership. Leadership commitment ties them together. Write each with one line of explanation.

How are Six Sigma and Kaizen different?

Six Sigma is a structured, data-driven project method (DMAIC) that aims to cut defects to about 3.4 per million opportunities. Kaizen is a continuous culture of small improvements by all employees. Six Sigma targets big variation reduction; Kaizen builds steady daily gains.

When do I use a p chart and when a c chart?

Use a p chart when you count defective items as a proportion of a sample. Use a c chart when you count the number of defects in one unit, such as flaws per metre of cloth.