Is/Is Not Analysis: Problem Definition for Root Cause Analysis

Is/Is Not analysis is the structured problem definition method that narrows root cause investigation by systematically documenting what conditions are present when a manufacturing failure occurs and what conditions are absent when it does not, using the contrast between the two columns to eliminate causal domains from the investigation before any root cause hypothesis is formed. Developed within the Kepner-Tregoe problem analysis framework by Charles Kepner and Benjamin Tregoe in the 1960s and subsequently embedded in both the 8D methodology and the DMAIC Analyze phase, Is/Is Not analysis prevents investigation teams from spending resources investigating causes that the evidence already excludes. The German Association of the Automotive Industry (VDA) recommends Is/Is Not analysis specifically in the D2 (problem description) and D4 (root cause analysis) disciplines of the 8D problem-solving process, recognizing it as the most effective tool for narrowing the causal domain before deeper investigation begins.

The core logic of Is/Is Not analysis is deceptively simple. A root cause must explain both what IS happening and what IS NOT happening. A proposed cause that would predict failures in conditions where failures are NOT occurring is not the root cause. It is a hypothesis that the evidence already contradicts. Systematically documenting the Is/Is Not contrast before forming hypotheses prevents teams from selecting causes that feel plausible but that the factual record of when and where failures do and do not occur already eliminates.

The Is/Is Not Framework: Four Dimensions

Is/Is Not analysis structures the problem description across four dimensions that collectively define the specific conditions under which the failure occurs and the adjacent conditions under which it does not. Each dimension generates two questions: what IS true about this dimension when the failure occurs, and what IS NOT true about this dimension when the failure does not occur.

What

The What dimension defines what the failure is, and what it is not.

IS: What specific product, component, part number, or process step is affected? What specific characteristic is failing: dimensional, surface, material, functional? What is the specific defect mode that is occurring?

IS NOT: What similar products, components, or characteristics are not failing despite being produced by the same process or handled by the same equipment? What defect modes that could occur from the same cause are not occurring?

The contrast between what is failing and what similar things are not failing is highly informative. If a dimensional defect is occurring only on Part Number X and not on Part Number Y produced by the same machine, the Is/Is Not contrast points investigation toward whatever is distinctive about Part Number X (its geometry, its material, its tolerance range) rather than toward the machine as a general cause.

Where

The Where dimension defines where the failure occurs and where it does not.

IS: Where in the facility does the failure occur: which line, which workstation, which machine, which shift location? Where on the product does the defect appear: which surface, which dimension, which assembly interface?

IS NOT: Which similar lines, workstations, machines, or product locations do not show the failure despite being candidates for the same cause?

Where the failure occurs and where it does not is frequently the most discriminating dimension in manufacturing investigation. A defect occurring only at Workstation 3 on Line B and not at any other workstation or line narrows the investigation to whatever is distinctive about Workstation 3 on Line B: its specific tooling, its fixture, its local environment, or its operator technique.

When

The When dimension defines when the failure occurs and when it does not.

IS: When did the failure first appear: which shift, which day, which production run? When during the production cycle does it occur: startup, steady state, end of run, after material changes? When was the last time the process produced conforming output?

IS NOT: Which time periods, shifts, or production cycle phases do not show the failure despite being exposed to the same process?

The When dimension frequently reveals triggering events: a process change, a material lot change, a maintenance activity, an operator change, or an environmental condition change that correlates with the onset of the failure. Identifying the point in time when conforming production became non-conforming production is often the most direct route to the root cause.

How Big (Extent)

The How Big dimension defines the scale and pattern of the failure.

IS: How many units are affected? What is the defect rate: is it consistent, increasing, or intermittent? What is the severity of the defect when it occurs?

IS NOT: What scales of failure are not occurring: is it scattered rather than systematic? Are certain lot sizes, production runs, or shift volumes not showing the defect?

The pattern of the failure's extent reveals whether the cause is constant (systematic defect rate), intermittent (sporadic cause), or growing (progressive cause such as tool wear or fixture drift).

Key Insight: Each Is/Is Not dimension generates both an IS statement (confirmed conditions of failure) and an IS NOT statement (confirmed conditions of non-failure). Both columns are required. The IS NOT column is where causal hypotheses are eliminated.

The Contrast Logic: What the IS NOT Column Reveals

The analytical power of Is/Is Not analysis comes from the contrast between the two columns, not from either column in isolation. A potential root cause must be consistent with both what IS happening and what IS NOT happening to remain a viable hypothesis.

The test for any proposed cause is: if this cause is present, would it produce failures in all the conditions listed in the IS column and not produce failures in any conditions listed in the IS NOT column? A cause that would predict failures in IS NOT conditions fails the test and is eliminated.

In practice, this contrast logic works as follows:

A team investigating a surface defect proposes that ambient humidity is the root cause. The Is/Is Not analysis shows that the defect IS occurring on the second shift but IS NOT occurring on the first shift. Both shifts work in the same facility with the same ambient humidity. Humidity cannot explain the shift-specific pattern. The humidity hypothesis is eliminated by the contrast, and investigation turns toward what is distinctive about the second shift: different operators, different material lots, different production rate, or different machine parameters.

This elimination process is what makes Is/Is Not analysis faster than open-ended brainstorming. Every hypothesis that fails the contrast test is removed from the investigation agenda before any resource is spent investigating it. The investigation resources that remain are concentrated on hypotheses that the evidence has not yet eliminated.

Key Insight: A valid root cause must explain the IS conditions and be absent in the IS NOT conditions. Any proposed cause that would predict failures where the evidence shows no failures is eliminated without investigation.

Is/Is Not Analysis in 8D and CAPA

Is/Is Not analysis integrates directly into the two structured problem-solving frameworks most commonly used for significant manufacturing quality failures.

In [8D Problem Solving: The Eight Disciplines Method for Manufacturing], Is/Is Not analysis appears in two disciplines. In D2 (problem description), the four-dimension Is/Is Not framework produces the specific, evidence-based problem statement that the rest of the 8D investigation builds on. A vague D2 problem statement produces a vague D4 root cause conclusion. Is/Is Not ensures D2 is precise enough to direct D4 investigation. In D4 (root cause analysis), the Is/Is Not contrast is used to test each root cause hypothesis against the factual record, eliminating hypotheses that contradict the IS NOT evidence before investigation resources are committed to testing them.

In [CAPA Systems in Manufacturing: Corrective and Preventive Action Explained], Is/Is Not analysis structures the problem statement in Stage 1 (problem definition and scope) before root cause investigation begins. The contrast between IS and IS NOT conditions defines the CAPA scope precisely, preventing the investigation from expanding into adjacent processes that the evidence already excludes and preventing it from narrowing prematurely to exclude conditions that the evidence has not yet eliminated.

Key Insight: Is/Is Not analysis in D2 determines the precision of D4. A vague Is/Is Not in problem description produces a broad, unfocused root cause investigation that is less likely to reach the actual root cause.

Is/Is Not vs Other Problem Definition Tools

Is/Is Not analysis is one of two problem definition tools used in manufacturing RCA. Understanding how it relates to [5W1H Method: Defining Problems for Root Cause Analysis] clarifies when each applies and how they complement each other.

5W1H (Who, What, Where, When, Why, How) is an open-ended problem description framework that gathers all relevant information about a failure to ensure the investigation team has complete situational awareness before analysis begins. It is comprehensive in information gathering but does not generate the contrast logic that eliminates causal hypotheses.

Is/Is Not analysis is a contrast-based framework that uses the same Who, What, Where, When dimensions as 5W1H but explicitly requires both the IS and IS NOT columns for each dimension. The contrast is what generates hypothesis elimination, the distinctive feature that gives Is/Is Not its specific investigative value.

In practice, the two tools are complementary: 5W1H gathers the full picture of the failure context, and Is/Is Not analysis extracts the contrasts within that picture that point toward and eliminate specific causes. Used together in the problem definition phase, they give an investigation team both comprehensive situational awareness and a narrowed causal focus before root cause hypothesis formation begins.

For problems with a straightforward single-cause structure, [What is the 5 Whys Root Cause Analysis Method?] can proceed after 5W1H without requiring Is/Is Not analysis. Is/Is Not analysis adds its greatest value when the problem has a complex or non-obvious causal pattern, when the failure occurs in some conditions and not others in ways that are not immediately explained by the visible process differences.

Key Insight: 5W1H gathers the full context. Is/Is Not extracts the contrasts within that context that eliminate hypotheses. Both are problem definition tools; only Is/Is Not generates causal elimination logic.

Common Is/Is Not Failures

Three failure modes consistently undermine Is/Is Not analysis in manufacturing investigations.

Leaving the IS NOT column blank. Teams document what IS happening thoroughly and then leave the IS NOT column incomplete or empty because identifying what is NOT happening feels less urgent than documenting what is. Without the IS NOT column, the analysis is a problem description, not a contrast analysis. The elimination logic that is Is/Is Not's primary value does not operate without both columns completed.

Populating IS NOT with assumptions rather than evidence. The IS NOT column must reflect confirmed conditions of non-failure, not assumed conditions. "IS NOT occurring on Line A" requires confirmation that Line A was actually observed to be producing conforming output during the period the failure appeared on Line B. An IS NOT statement based on assumption rather than observation does not eliminate the cause. It creates false confidence that a condition has been ruled out when it has not been confirmed.

Stopping at problem description without testing hypotheses. Is/Is Not analysis produces a narrowed investigation agenda. It must be followed by explicit hypothesis testing: for each potential root cause, the team confirms whether it satisfies both the IS and IS NOT conditions. Teams that complete the Is/Is Not matrix and then proceed directly to corrective action selection without hypothesis testing use Is/Is Not as documentation rather than as analytical elimination logic.

Key Insight: The IS NOT column is not optional. Without it, Is/Is Not analysis is a problem description, not a contrast analysis. The elimination logic requires both columns.

Within the Lean System

Connection to Lean Principles

Is/Is Not analysis operationalizes the lean principle of fact-based decision making by replacing assumption-based hypothesis selection with evidence-based hypothesis elimination. In lean investigation, genchi genbutsu (go and see for yourself) is the instruction to gather the factual Is/Is Not evidence at the gemba rather than constructing the contrast from memory and assumptions in a conference room. The IS NOT column in particular requires confirmed observation of conditions where failures do not occur, which means the investigation team must physically verify non-failure conditions at the actual production location.

Connection to Lean Tools

Is/Is Not analysis integrates directly with [8D Problem Solving: The Eight Disciplines Method for Manufacturing] in D2 and D4, with [5W1H Method: Defining Problems for Root Cause Analysis] as its complementary problem gathering tool, and with [What is Root Cause Analysis in Lean Manufacturing?] as the methodological context within which Is/Is Not serves as a pre-investigation narrowing step. [Non-Conformance Reports: Managing Quality Deviations in Manufacturing] provides the production failure data that populates the IS column of each dimension. The IS NOT evidence requires direct observation or confirmed production records showing conforming output in adjacent conditions.

Connection to Continuous Improvement

Is/Is Not analysis accelerates the [PDCA Cycle: The Foundation of Continuous Improvement] Plan phase by reducing the number of hypotheses that require investigation before the verified root cause is identified. Every hypothesis eliminated by the Is/Is Not contrast logic is investigation time saved. Over multiple improvement cycles, teams that consistently apply Is/Is Not analysis before forming hypotheses identify root causes faster, implement corrective actions sooner, and verify effectiveness earlier than teams that begin investigation with open-ended brainstorming. The cumulative effect is a faster PDCA cycle rate, which means more improvement cycles completed per year.

Frequently Asked Questions

What is Is/Is Not analysis in manufacturing? Is/Is Not analysis is the structured problem definition method that narrows root cause investigation by systematically documenting what conditions are present when a failure occurs (IS) and what conditions are absent when it does not (IS NOT) across four dimensions: What, Where, When, and How Big. The contrast between the two columns eliminates causal hypotheses that would predict failures in conditions where the evidence shows no failures, focusing investigation resources on hypotheses that remain consistent with the factual record.

What are the four dimensions of Is/Is Not analysis? The four dimensions are What (what specific product, component, or characteristic is failing and what is not), Where (where in the facility or on the product the failure occurs and where it does not), When (when in time or in the production cycle the failure appears and when it does not), and How Big (what scale and pattern the failure exhibits and what scales and patterns are not present). Each dimension generates both an IS statement confirming failure conditions and an IS NOT statement confirming non-failure conditions.

How does Is/Is Not analysis eliminate root cause hypotheses? Any proposed root cause must be consistent with both the IS conditions (it must predict failures where failures occur) and the IS NOT conditions (it must not predict failures where failures do not occur). A proposed cause that would predict failures in IS NOT conditions is eliminated from the investigation without further resource investment. This contrast-based elimination logic is the analytical mechanism that makes Is/Is Not analysis faster than open-ended brainstorming.

When should Is/Is Not analysis be used in root cause investigation? Is/Is Not analysis is most valuable when a failure has a complex or non-obvious causal pattern, occurring in some conditions and not others in ways that are not immediately explained by visible process differences. It is used in the problem definition phase before hypothesis formation, specifically in D2 of the 8D problem-solving process and in the problem statement stage of CAPA. It is less necessary for straightforward single-cause failures where the 5 Whys method is sufficient.

What is the difference between Is/Is Not analysis and 5W1H? 5W1H is an open-ended information gathering framework that documents the Who, What, Where, When, Why, and How of a failure to ensure comprehensive situational awareness. Is/Is Not analysis is a contrast-based framework that uses the What, Where, When, and How Big dimensions but requires both IS and IS NOT columns for each, generating the hypothesis elimination logic that 5W1H alone does not produce. They are complementary: 5W1H gathers the full context, Is/Is Not extracts the contrasts that eliminate causes.