M.Jabari 2005M.Jabari 2005

 «Do what you have written and write

what you have done» 

It is generally useful first to try to classify the error as It is generally useful first to try to classify the error as

random or systematicrandom or systematic. .

The set of rules recommended The set of rules recommended by westgard (1981 )by westgard (1981 ). .

1:2S : one observation in the warning zone

(Outside 2S)

1:3S : one observation in the rejection zone

(Outside 3S)

2:2S : two consecutive control

observations in the warning zone, on the

same side of the mean (Outside 2S)

R:4S : two consecutive control observations in the

warning zone. ( The range of two results is greater than 4 SD)

4:1S : Four consecutive results outside

1SD on the same side of the mean.

10M : 10 consecutive observations on the

same side of the mean

CONTROLDATA

1:2s

1:3s 2:2s R:4s 4:1s 10 X

IN-CONTROL ACCEPT RUN

OUT-OF-CONTROL REJECT RUN

NO

YES

YES

NO NO NO NO

YES YES YES

NO

YES

When a systematic error is present , When a systematic error is present , the cusum values will steadily the cusum values will steadily

increaseincrease. .

The slope of the line will be related The slope of the line will be related to the size of the systematic errorto the size of the systematic error. .

Cusum techniques generally provide Cusum techniques generally provide

better detection of systematic errors better detection of systematic errors

than levey-jennings chartsthan levey-jennings charts . .

NOGLUCOSE mg%MEANX-M(X-M )2

110010000

298100-24

3102100+24

499100-11

5101100+11

610010000

798100-24

8101100+11

997100-39

1099100-11

1198100-24

12101100+11

1310010000

1499100-11

1599100-11

16101100+11

1797100-39

1810010000

19101100+11

2099100-11

)X-M( = -10

)X-M( = 442

SD =)X-M(2

n-1

SD = 44

19

SD = 1.7

94

96

98

100

102

104

106

GLUCOSE mg% 100 98 102 99 101 100 98 101 97 99 98 101 100 99 99 101 97 100 101 99

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

+3SD

+2SD

+1SD

-1SD

-2SD

-3SD

NO.GLUCOSE mg%MEANX-MCUSUM

110010000

298100-2-2

3102100+20

499100-1-1

5101100+10

610010000

798100-2-2

8101100+1-1

997100-3-4

1099100-1-5

1198100-2-7

12101100+1-6

131001000-6

1499100-1-7

1599100-1-8

16101100+1-7

1797100-3-10

181001000-10

19101100+1-9

2099100-1-10

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

GLUCOSE mg% 0 -2 0 -1 0 0 -2 -1 -4 -5 -7 -6 -6 -7 -8 -7 -10 -10 -9 -10

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

-3SD

+2SD

+1SD

-2SD

-1SD

-10 SD

Accuracy control Recovery

Patients mean

Linearity

Glucose:

Specimen 1 : 150 mg%

Specimen 2 : 100 mg%Add together

Expected value : 250 mg%

Observed value : 230 mg%

% Recovery = 100 - 8 = 92%

Ideal recovery is greater than 95% Ideal recovery is greater than 95%

% Bias =250 - 230

250X 100 = 8

In this method mixed two specimen with In this method mixed two specimen with

different ( one high and other low) different ( one high and other low)

concentration ,and reassayconcentration ,and reassay. .

The chart of concentration and absorbaance The chart of concentration and absorbaance

must be strightforwardmust be strightforward. .

Good area < 1s

1s < warning area < 2s

rejection area > 2s

The dispersion is increased (CV 2, CV 3)

Accurate but not precise

Not systematic

The dispersion is the same

The target is moving

Precise but not accurate

Systematic

Not accurate and not

precise…

Systematic &non

Systematic bias…