星期四, 8月 23, 2007

Rounding Dilemma in Two-Dimension Situation

Please consider following example:

Before Rounding:

 

 

 

 

Jan

Feb

Cum

Item 1

12.534145

8.126270

20.660415

Item 2

14.004458

7.119500

21.123958

Total

26.538603

15.245770

41.784373

 

 

 

 

Rounded Version

 

 

 

 

Jan

Feb

Cum

Item 1

12.53

8.13

20.66

Plan 2

14.00

7.12

21.12

Total

26.54

15.25

41.78

 

There is no problem in calculation in "Before Rounding" version.

 

However, user may report that some problem on Rounded version. Because 26.54+15.25 <> 41.78

But, if we patch the data become 41.79, then it become another problem since 20.66+21.12<> 41.79

It is a perception dilemma because we did not recognized that all version are rounded values rather than actual values.  

 

May be you may suggest to do rounding before all calculations, however, please aware that cumulative error will become very large, as we have more than 5,000 of item in calculation . 

Let me compare the "error"

Method

Error due to Rounding

Error due to Human Perception

Rounding only on display (Current method)

0.00 (as no rounding in calculation)

0.005

Rounding before calculation

=0.005* 5,000 = 25.00

0.00

 

Conclusion:

The "Rounding Issues" is because of a wrong perception from human rather than system error.

 

 

 

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