Subjective Root Cause Analysis


The subjective root cause analysis tools are used to systematically identify and subjectively weigh the correlation of the inputs (x’s) to the problem, Y.


Determine the most important known and hidden root causes (when data is not necessarily available) to analyze their importance and relationships in the ANALYZE phase. These tools take all the controllable inputs (causes), and filter them down to the vital few that have the most impact on closing the gap written in the project contract.

Sometimes not all data can be gathered for a number of reasons, the data may be flawed, or there are hidden causes that need to be discussed within the team. Synergy and knowledge sharing is needed to properly understand and weigh the impact root causes have on the output.

Use these tools in this order, if there are few x’s then the correlation matrix can be skipped. Each tool narrows the focus to the primary inputs, x’s, to the problem. The primary inputs, x’s, are referred to as the Key Process Input Variables, KPIV’s.

1) FISHBONE – includes all inputs, x1, x2, x3……..xn.

2) CORRELATION MATRIX – also called Cause/Effect Matrix and Prioritization Matrix

3) FMEA – Failure Mode and Effects Analysis

Filtering of the inputs to the vital few

One helpful and simple procedure to help a team drill down to the root cause is the 5-WHY tool. This is used to drill down and reveal the root causes of unplanned downtime, form errors, injuries and accidents, quality defects, late deliveries, and more.

There are several methods to help find the root causes of variation. These are more traditional tools that are commonly used in problem solving techniques due to the ability to break complex problems into small scopes and make them manageable so everyone can participate.

The goal is to capture all of the inputs, big or small. Funnel them them down throughout the subjective tools and scoring system with cross functional representation and then take the few key inputs (KPIV's) and begin to ANALYZE them.

Problem solving techniques, such as A3, include subjective root cause tools, basic process mapping and value stream mapping, and most importantly emphasize clear understanding of the problem, gap, corrective action, and accountability to control.

A3 is a key component of Toyota problem solving process that applies to all levels of the workforce. The Plan-Do-Check-Act cycle is fully encompassed in this simple tool. The entire scope of the cycle from problem statement all the way to completed improvements are hand written on one large sheet of paper.

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Basic Statistics
Process Mapping
Capability Studies
Cause & Effect Matrix
Multivariate Analysis
Central Limit Theorem
Confidence Intervals
Hypothesis Testing
T Tests
1-Way Anova Test
Chi-Square Test
Correlation and Regression
Control Plan