In markets with lots of activity, communications investment may be necessary just to maintain a brand’s sales. If this is the case, the communications should be considered effective if the brand’s sales can be maintained with a share of category spend similar to or lower than its share of market.
If ad spend or quality are high enough compared to competitors, the brand has a chance of growing. If spend is low or ad quality poor, the brand is likely to decline.
This short video explains the concept in more detail.
For further insights about media planning, check out this short article or listen to this audio clip.