Build a comparison you can reproduce
Save the current report and its comparison before interpreting the percentage. Record the source, the week ending, whether the observation is estimated or administrative, and the unit. If a publisher later revises the earlier value, keep a note of the revision rather than silently comparing with a different baseline.
| Hypothetical observation | Tonnes | Question answered |
|---|
| Current week | 50,000 | What arrived in this interval? |
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| Previous week | 40,000 | Has recent flow improved? |
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| Comparable prior-year week | 80,000 | How does the seasonal comparison look? |
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| Current season cumulative | 180,000 | How much has arrived since the chosen start? |
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| Prior season at matching cut-off | 300,000 | How large is the accumulated difference? |
|---|
In this invented example, weekly flow improves 25%, the weekly annual comparison is −37.5%, and the cumulative annual comparison is −40%. None cancels the others. They describe different intervals.
When the comparison should remain unavailable
A missing prior-year figure does not mean last year's arrivals were zero. A zero denominator does not support an ordinary percentage-change calculation. A differently defined week may be useful background, but should not silently be treated as equivalent.
A week spanning the season boundary needs particular care. Do not add an entire weekly total to an October-start series unless the report actually assigns that quantity to the new season. Summing rounded weekly estimates can also differ from an independently reported cumulative total.
From a number to a useful question
If the current week improves but the cumulative shortfall widens, ask whether the improvement was large enough to catch up. If the annual shortfall narrows, investigate whether current flow strengthened or the comparison week was unusually weak.
Then check the physical explanation. Crop timing, transport and commercial delivery decisions can influence port flow. Arrivals are evidence about movement, not a completed census of production.
Can you combine exporter and official estimates? Keep them as separately labelled series unless their compatibility is established. Can you infer demand from arrivals alone? No: compare processing and destination inventories separately.
Use the comparison tool, arrivals-versus-production guide and stock-and-flow walkthrough. All quantities in this addition are hypothetical.