• What is Data ?

Data is a numerical expression of an activity.

Conclusions based on facts and data are necessary for any improvement.

-K. Ishikawa

If you are not able to express a phenomenon in numbers, you do not know about it adequately.

-Lord Kelvin

DATA GATHERINGDATA GATHERING

TYPES OF DATATYPES OF DATACONTINUOUS DISCRETE

Measurable

e.g. :Length, Temperature

Subjective Assessmente.g. :Score in a beautycontest

Countablee.g. :Number of defects

Data if properly collected

• Least influenced by individual biases

• Could be subject to critical analysis

• Generally beyond language barriers and therefore universal in expression.

WHAT IS THE DIFFERENCE WHAT IS THE DIFFERENCE BETWEENBETWEEN

A SHAFT DIAMETER

THE NUMBER OF SHAFTS REJECTED FOR OVERSIZE

DIAMETER

The diameter of a

shaft can take any

value ever after the

decimal point e.g..

19.055, 19.0516

etc..

Data related to this

type of parameters

are called

Continuous data.

The number of shaft rejected has necessarily to be a whole number. e.g.. 0, 2, 7, 10 numbers rejected etc..

Data related to this

type of parameters are

called Discrete data.

HOW DO YOU DISTINGUISH BETWEEN HOW DO YOU DISTINGUISH BETWEEN

CONTINUOUS AND DISCRETECONTINUOUS AND DISCRETE

CONTINUOUS DISCRETE

•They are real numbers

•Normally, they are measured values

•They can not take a single value. There is an area associated with it

•They are continuous

•Requires less sample size

• They are whole numbers

• Normally, they are counted values

• They can take only ‘Zero’ or non-fractional positive values

• They are in steps of ‘1’• Requires more sample

size to have the more precision

WHICH OF THE BELOW ARE WHICH OF THE BELOW ARE CONTINUOUS AND DISCRETE CONTINUOUS AND DISCRETE

DATA?DATA?• Width of sheet

• No. of liners thinned

• Tubes rejected by Go- Nogo Gauge

• Diameter of Piston

• Height of a Man

• Sheet thickness

• Out of 100 sheets the numbers that meet the thickness 4 0.9

• Time taken to process a purchase order

• No. of bugs in a program

OBJECTIVES OF DATA COLLECTIONOBJECTIVES OF DATA COLLECTION• To know and quantify the status

• To monitor the process

• To decide acceptance or rejection

• To analyse and decide the course of action

HOW TO COLLECT DATA ?HOW TO COLLECT DATA ?

• Define the purpose

• Decide the type of analysis

• Define the period of data collection

• Is the the required data already available ?

FOR PROPER DATA COLLECTION...FOR PROPER DATA COLLECTION...

• Proper sampling procedure

• Proper choice of instruments

• Calibration of instruments used

• Availability of standards for sensory characteristics

• Adequate lighting and other test/inspection facilities.

• Record all relevant information

• No two things in nature are alike. • This is also true for manufactured products. • This dissimilarity between two products for the

same characteristic is called variation.

• The variation may be or can be made to be so small so as to make the product SEEM similar.

• When we say that 2 things are similar we actually mean that it is not possible to measure the variation present within the accuracy of the existing measuring equipment.

• Variation between 2 products are compared for SIMILAR features or characteristics.

WHAT IS VARIATION ?WHAT IS VARIATION ?

• Variations among pieces at the same time

• Variations across time

TYPES OF VARIATIONTYPES OF VARIATION

This man wants to reach his work place by 6.55 a.m.. But he can not do so, exactly at 6.55 a.m. daily. Sometimes he reaches earlier (but almost never before 6.50 a.m.). Sometimes he reaches later (but almost never after 7.00 a.m.). WHY ?

6.50 6.55 7.00

6.55 a.m. 5 minutes.

OF CERTAIN FACTORS WHICH• Affect the time he takes • He cannot control• Vary randomly

e.g. The traffic you encounter under normal course of travel

THE VARIATION THAT OCCURS DUE TO THESE KIND OF FACTORS IS CALLED INHERENT VARIATION OR COMMON CAUSE VARIATION OR WHITE NOISE.e.g.. m/c vibration,tool wear etc.

THIS IS BECAUSE....THIS IS BECAUSE....

UNDER NORMAL UNDER NORMAL SCHEME OF OPERATIONSCHEME OF OPERATION

InherentVariability(white noise)

Aimed value

Minimum deviation

Maximum deviation

6.30

TODAY HE IS EARLY !

WHY ?

PROBABLY BECAUSE :• His watch was running fast.• He got a lift.• His bus driver took a

shortcut.• He stayed over in the

colony.• He had some important work

to be finished before 7.30.These causes are characteristic of a specific circumstance and do not occur in the normal scheme of actions.

Variation due to these types of reasons is called assignable or special cause variation or black noise

GRAPHICAL DISPLAY OF GRAPHICAL DISPLAY OF VARIABILITIESVARIABILITIES

InherentVariability

Assignable Variability

Assignable Variability

TOTAL VAR I A B I L I T Y

Assignable Variability

Assignable Variability

Aimed Value

CASE I

CASE II CASE III

(Black noise)

COMMON PROBLEMS WITH COMMON PROBLEMS WITH MEASUREMENTSMEASUREMENTS•Problems with the measurements themselves

1.Bias or inaccuracy: The measurements have a different average value than a “standard” method.

2.Imprecision: Repeated readings on the same material vary too much in relation to current process variation.

3. Not reproducible: The measurement process is different for different operators, or measuring devices or labs. This may be either a difference in bias or precision.

4. Unstable measurement system over time: Either the bias or the precision changes over time.

5. Lack of resolution: The measurement process cannot measure to precise enough units to capture current product variation.

DESIRED MEASUREMENT DESIRED MEASUREMENT CHARACTERISTICS FOR CHARACTERISTICS FOR

CONTINUOUS VARIABLESCONTINUOUS VARIABLESGood accuracy if

difference is small

Standard value

Observed value

Data from repeated measurement of

same item

Good repeatability if variation is small *

1. Accuracy

The measured value has little deviation from the actual value. Accuracy is usually tested by comparing an average of repeated measurements to a known standard value for that unit.

2. Repeatability

The same person taking a measurement on the same unit gets the same result.

3. ReproducibilityOther people (or other instruments or labs) get the same result you get when measuring the same item or characteristic.

* Small relative to a) product variation

andb) product tolerance (the width of the product specifications)

Data from Part X

Data Collector 1

Data Collector 2

Good reproducibility if

difference is small *

Data from Part X

DESIRED MEASUREMENT DESIRED MEASUREMENT CHARACTERISTICS FOR CHARACTERISTICS FOR

CONTINUOUS VARIABLESCONTINUOUS VARIABLES

4. StabilityMeasurements taken by a single person in the same way vary little over time.

Time 1

Time 2

Good stability if difference is

Small*

Observed value

Observed value

* Small relative to a) product variation

andb) product tolerance (the width of the product specifications)

DESIRED MEASUREMENT DESIRED MEASUREMENT CHARACTERISTICS FOR CHARACTERISTICS FOR

CONTINUOUS VARIABLESCONTINUOUS VARIABLES

5. Adequate Resolution

There is enough resolution in the measurement device so that the product can have many different values.

5.1 5.2 5.3 5.4 5.5X X

XXX

XXXXXX

XXX

XX

Good if 5 or more distinct values are observed

DESIRED MEASUREMENT DESIRED MEASUREMENT CHARACTERISTICS FOR CHARACTERISTICS FOR

CONTINUOUS VARIABLESCONTINUOUS VARIABLES

IMPROVING A IMPROVING A MEASUREMENT SYSTEMMEASUREMENT SYSTEM•A measurement system consists of

• Measuring devices

• Procedures

• Definitions

• People

•To improve a measurement system, you need to

• Evaluate how well it works now (by asking “how much of the variation we see in our data is due to the measurement system?”).

• Evaluate the results and develop improvement strategies.

NOTE ON CALIBRATING NOTE ON CALIBRATING MEASUREMENT EQUIPMENTMEASUREMENT EQUIPMENT• Measurement instruments should only be recalibrated when they show

special cause evidence of drift. Otherwise, variation could be increased by as much as 40%. This is because adjusting for true common cause variation adds more variation (Deming’s rule 2 of the funnel).

Measurements taken from stable instrument

Measurements taken with stable instrument recalibrated before each reading