Kill ratio is an excellent statistic. It is easily measurable and provides an apparent insight into how well various units fight whilst missing the major point. The object of a war is not to inflict casualties on the opposition. The object of a battle is not necessarily to inflict maximum casualties on the enemy. The object of both is to destroy the enemy’s ability to resist you. As an example, consider the Battles of Kursk and Monte Cassino.
Kursk
Soviet killed/wounded/captured: 860 000
German killed/wounded/captured: 200 000
Ratio: 4.3:1 Soviet:German casualties.
Yet Kursk cannot be described as a victory for the Germans in any sense of the word.
Monte Cassino
Allied killed/wounded/captured: 54 000
German killed/wounded/captured: 20 000
Ratio: 2.7:1 Allied:German casualties.
Monte Cassino, although costly, is considered an Allied victory as it enable the advance on Rome to continue.
In both these cases, although one side took far higher casualties than another, that side achieved victory. Simple comparison of casualties is insufficient to determine victory. Now consider the Battle of Kohima.
Battle of Kohima
wikipedia
UK Ministry of Defence
Allied killed/wounded/captured: 4000
Japanes killed/wounded/captured: 7000
Ratio: 1.75:1 Japanese:Allied casualties.
The small number of casualties on both sides, as well as the low kill ratio, serves to mask the importance of this battle. It is considered to be the turning point in the Burma campaign, halting the Japanese advance on India. Earl Louis Mountbatten described it as ‘probably one of the greatest battles in history… in effect the Battle of Burma… naked unparalleled heroism… the British/Indian Thermopylae’
What has been demonstrated is that casualty statistics are insufficient to judge the success of a battle or war. They are not even necessarily indicators of who won. What counts in a battle is the effect on the enemy’s ability to resist your will. This can be achieved through attrition of the enemy’s manpower and resources, or as in more modern warfare, by removing his ability to fight - Manouevre Warfare.
For further reading, see also what the interweb has on ‘Effects Based Operations’.