Part 6 · How do you read a CNA result?
Module 12 · Reading CNA notation
Don't panic at the algebra
- Read a CNA formula out loud as an ordinary sentence.
- Translate the symbols * + and the arrow into plain words.
- Turn any solution formula into something a colleague would understand.
Most people meet their first CNA result and feel their stomach drop. The screen shows something like this, and it looks like algebra homework you thought you had escaped:
A*B + C*D ↔ Y
Take a breath. There is nothing to fear here, because a CNA formula is just a sentence wearing a lab coat. Once you know the three words it is built from, you can read any result in the course, and any result your own data ever produces.
The whole vocabulary, in three words
Every CNA formula is made of three little symbols. That is the entire language. Learn these and you are fluent.
| Symbol | Say it as | It means |
|---|---|---|
| * | "and" | these conditions occur together, in the same case |
| + | "or" | this is a separate route to the same outcome |
| ↔ | "goes with" | the left side tracks the outcome on the right |
So that scary formula A*B + C*D ↔ Y simply says: "When you have A and B together, or C and D together, you tend to find Y." That's it. A sentence about two recipes for the same result.
A note for the precise: the double arrow ↔ is technically an equivalence. It says the left side is both sufficient for the outcome (where you see the combination, you see Y) and, taken as a whole, necessary for it (where you see Y, you find one of these combinations). "Goes with" is a faithful shorthand for that, and you will meet the full story in the model-evaluation modules.
Read it like a sentence
Here is the trick that makes everything click. Swap the letters for the real conditions, read left to right, and say the symbols out loud as their plain words. Watch a real immunization formula turn into an ordinary observation:
Train * Cold * Super ↔ Coverage
Trained staff AND a working cold chain AND supervision, goes with coverage
Read fully: facilities with trained staff, a functioning cold chain, and supportive supervision consistently achieved high coverage. Notice you didn't lose anything by saying it in words. You gained a sentence your director can actually act on. The formula and the sentence are the same statement, just dressed differently.
A recipe card reads "flour + butter + sugar." Nobody panics at that. CNA notation is a recipe card for outcomes: the * joins the ingredients that have to go in together, the + separates one recipe from a different recipe that also works, and the arrow points at the cake. You have been reading recipes your whole life. This is the same skill.
One more, with two pathways
When a formula has a + in it, that is equifinality showing up in the algebra: two different roads to the same place. Read each side as its own little sentence, joined by "or":
NoCold*NoSuper + NoComm*NoOutreach ↔ LowCov
Out loud: "Low coverage goes with a broken cold chain and missing supervision, or with no community mobilisation and no outreach." Two recipes for the same disappointing result. A district could land in low coverage by either route, which is exactly why you need to know which route a given place is on before you spend a naira fixing it.
Lower-case letters mean absence. Cold means the cold chain is working; cold (or a name like NoCold) means it is broken. When you read a formula aloud, always check the case, because "supervision is present" and "supervision is absent" are opposite stories with opposite fixes.
Take the very first formula in this module, A*B + C*D ↔ Y.
- Can you now say it out loud as a sentence, without looking at the table?
- Swap in conditions from your own program. Does the sentence describe something you have actually seen in the field?