Monthly v annual, downside v upside... when it comes to rates of change, COVID19 is a good reminder of how hard, intuitively, arithmetic can be...
Take Irish retail sales. Gloriously, monthly changes in retail sales are booming, up 29.5% m/m in volume and 28.4% in value. A 'V-shaped' thingy. Un-gloriously, year on year the sales are 26.6% in volume and 29.1% in value. But here's the ugly thingy: suppose a year ago you were retailing 1 unit (in volume or value). Annual rate of change in these was around 2.55% over 2016-2019 for value and 4.4% in volume. Which means you were 'rationally' expecting to be selling 1.0255 units in value and 1.044 units in volume around this time 2020. You are selling, instead 0.705 units in value and 0.734 units in volume. You have, prudently, planned your investment and spending allocations, based on similar expectations. Your reality is that you are down 31.3 percent on where you were supposed to be in value and 29.7 percent in volume. Notice the 'wedge' between volume and value. Deeper deterioration in value than in volume means not only that your revenue fell off, but that you are working harder to deliver on what revenue you do derive. In basic terms, you now need to be selling roughly 5 percentage points more of volume to derive the same euro value.
In simple analogy terms, you are trying to swim back to shore in a gale-force head wind, with a 12 feet swell, and against a roaring riptide. But otherwise, it's a 'V-shaped' looking thingy...
