Customer Identification
Key Takeaways
- Customers are the people or organizations that receive the process output; they may be external (market, end user, patient, client) or internal (next process, downstream department).
- Internal customers still define requirements; treating “only the paying customer” as the sole customer under-scopes many Green Belt projects.
- Project failure harms customers through defects, delays, higher cost, poor service, safety risk, and lost trust—and those harms cascade to the business.
- SIPOC and value-stream views help list primary, secondary, and sometimes hidden customers of a process.
- When customers conflict, translate needs into measurable CTQs and prioritize with business strategy and stakeholder analysis—not by ignoring internal customers.
Customer Identification (CSSGB BoK II.B.1 — Apply)
Quick Answer: Customers receive the process output. External customers sit outside the organization (buyers, patients, regulators-as-clients in some contexts, end users). Internal customers are the next processes or functions that receive your work. Misidentifying customers leads to wrong VOC, wrong CTQs, and projects that “succeed” on internal metrics while the real receiver still suffers.
Voice of the Customer starts with a deceptively hard question: whose voice? BoK II.B.1 is at the Apply level—name internal vs external customers in scenarios and reason about impact if the project fails.
What “Customer” Means in Six Sigma
In DMAIC language, a customer is anyone who receives an output of the process under study. That definition is broader than “the person who pays the invoice.”
- The external customer is outside the enterprise boundary: consumer, B2B client, patient, citizen, passenger, policyholder.
- The internal customer is inside the enterprise: the next workstation, warehouse, billing team, call center, clinical unit, or sister plant that must use your output as their input.
Both matter. Lean and Six Sigma teach that the next process is your customer. If machining sends burrs to assembly, assembly is an internal customer with real requirements (clean edges, correct count, on-time delivery to the cell).
Internal vs External Customers
| Type | Who | What they typically care about | VOC examples |
|---|---|---|---|
| External | End user, buyer, client, patient | Fit, function, reliability, price, delivery, service, safety | Surveys, complaints, NPS, warranty, social reviews |
| Internal | Downstream process or department | Completeness, accuracy, timing, format, ease of use as input | Handoff checklists, reject tags, service-level agreements between departments |
| Intermediate / channel | Distributor, retailer, referring physician | Packaging, lead time, information accuracy | Channel scorecards, returns from stores |
Some processes serve multiple customer layers. A hospital lab’s external customer may be the patient (and clinician acting for the patient), while the floor nurse is an internal customer of turnaround time and report clarity. A Green Belt project on lab turnaround must hear both: clinicians for clinical usability, patients for experience and access, and operations for capacity constraints.
Worked identification from a SIPOC
Process: Order-to-cash credit review for industrial equipment.
| SIPOC element | Example |
|---|---|
| Suppliers | Sales, ERP master data, credit bureau |
| Inputs | Quote, customer master, credit report |
| Process | Credit check → approve/deny/limit |
| Outputs | Credit decision, limit, notes in ERP |
| Customers | Sales (internal), order management (internal), the buying company (external), finance/risk (internal stakeholder-customer of risk quality) |
If the team only interviews the CFO’s risk staff and never sales or the B2B buyer’s experience of onboarding delay, VOC will over-weight risk controls and under-weight speed-to-order—an incomplete customer set.
Primary, Secondary, and Hidden Customers
Not every receiver is equal:
- Primary customer: main reason the process exists (patient receiving a discharge, client receiving a deliverable).
- Secondary customers: others who receive outputs (billing, regulators requiring a record, support teams).
- Hidden customers: often forgotten internal groups (IT operations receiving tickets from a “fixed” process that now creates new work; night shift inheriting a day-shift redesign).
Exam tip: When a stem lists several parties, ask “Who receives the output?” Sponsors and process owners are critical stakeholders, but they are customers only when they also receive the process output. A VP sponsor who never touches the widget is usually not the customer of the machining process.
How Project Failure Affects Customers
Green Belts should be able to trace failure modes to customer harm:
| If the project fails to improve (or makes things worse)… | External customer impact | Internal customer impact |
|---|---|---|
| Defects remain high | Returns, safety risk, dissatisfaction, brand damage | Rework, firefighting, overtime |
| Lead time stays long | Late delivery, lost sales, churn | Starved downstream processes, expediting |
| Variation stays high | Unpredictable quality/service | Unstable schedules, excess inventory buffers |
| Wrong solution deployed | Confusing features, new failure modes | Broken handoffs, shadow systems |
| Gains not sustained | “It worked for a month” erosion of trust | Return to tribal workarounds |
Business impact follows customer impact: lost revenue, warranty cost, cost of poor quality (CoPQ), regulatory exposure, and employee burnout from internal customer chaos.
Worked scenario — failed medication-reconciliation project
A Green Belt aims to reduce discharge medication errors.
- External customers: patients (and families) who receive the med list; harm if wrong drug/dose.
- Internal customers: outpatient pharmacy, primary-care clinic, home-health nurse receiving the discharge summary.
- Failure effects: patient adverse events (external), clinic rework and callbacks (internal), possible reportable events and liability (organization).
Identifying only “the hospital” as the customer is too vague for VOC and CTQ work. Identifying only pharmacy without patients misses the primary external receiver of safe therapy.
Practical Steps to Identify Customers
- Start with the process boundary (SIPOC/process map): list every output and who receives it.
- Walk the value stream: ask each step, “Who is the next customer of this output?”
- Separate payers, users, and choosers when they differ (parents choose a pediatric service; child uses it; insurer pays).
- Check complaints and returns: who files them? That party is often a real customer voice.
- Validate with the process owner and sponsor: confirm primary vs secondary so scope matches strategy.
- Flag conflicting requirements early: internal cost goals vs external service promises—resolve via prioritization and CTQs, not by pretending one customer does not exist.
Linking Customer Identification to VOC and CTQs
Customer identification is the on-ramp to II.B.2 data collection and II.B.3 requirements (CTQ, QFD, Kano):
- Wrong customers → surveys of the wrong population
- Only external voices → internal handoff failures ignored
- Only internal voices → elegant process that customers still leave
Apply-level exam moves:
- Label parties as internal customer, external customer, or non-customer stakeholder
- Explain impact of failure in customer terms (delay, defect, risk), not only in “project red status”
- Choose the customer set that matches the project Y (if Y is on-time delivery to the distribution center, the DC is at least an internal customer even if the brand’s end consumer is also external)
Identify customers before you collect VOC. Otherwise you will measure the wrong voices with great precision.
In a manufacturing cell, finished subassemblies are handed to Final Assembly, and completed units ship to a retail chain that sells to consumers. Who are the internal and external customers of the subassembly cell’s primary output?
A Green Belt project to cut hospital lab turnaround time fails and times remain long. Which statement best describes customer impact?