Did you know that rounding in Cognos does not behave in the usual manner? By default, IBM Cognos Business Intelligence uses the round half to even rule when rounding numbers.
What is Round Half to Even Rule?
This rounds to the nearest value; if the number falls midway it is rounded to the nearest value with an even (or zero) least significant bit, which occurs 50% of the time. For example:
Original Number | Traditional Rounding | Rounded to 0 decimal places |
+11.5 | +12 | +12 |
+12.5 | +13 | +12 |
-11.5 | -12 | -12 |
-12.5 | -13 | -12 |
The round half to even rule is widely used in bookkeeping. Furthermore over a large dataset this style of rounding reduces rounding errors.
Other Rounding Rules
There are many different rounding rules. Each has their purpose. The table below summarises the key rounding rules:
Rule | Description | Examples | |||
-12.5 | -11.5 | 11.5 | 12.5 | ||
halfEven | Round to nearest neighbor, where an equidistant value is rounded to the nearest even neighbor. This is the default rule. | -12 | -12 | 12 | 12 |
halfDown | Round to nearest neighbor, where an equidistant value is rounded down. | -13 | -12 | 11 | 12 |
halfUp | Round to nearest neighbor, where an equidistant value is rounded up. | -12 | -11 | 12 | 13 |
ceiling | Round to a more positive number. | -12 | -11 | 12 | 13 |
floor | Round to a more negative number. | -13 | -12 | 11 | 12 |
down | Round towards zero. | -12 | -11 | 11 | 12 |
up | Round away from zero. | -13 | -12 | 12 | 13 |
Changing Rounding Rules
While Cognos uses the halfEven rule, precision regulations in some industries require different rounding rules (for example, the round half up rule). With IBM Cognos Business Intelligence 10.2 and above, you can now choose a rounding rule to comply with the precision regulations that apply to you.
To do this follow these steps:
Note that rounding rules can only be applied to an entire server and you cannot override for a package, cube or report. If you want to change towards a more “traditional” rounding then you need to set “halfup”.
