In this discussion, I saw a phrase "causal estimand", I try to google it but I cannot find a meaning fitting this context.

Now it's important to note that the causal estimand is plausibly unbiased if we assume constant treatment effects. However, if effects change over time, especially for the early-receivers, then it may completely offset the stability of the trends as the late-receivers become eligible for treatment

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    Probably a spelling misake for "causal estimand". I don't know what that it either. It is a specialist term of statistics psiweb.org/docs/default-source/default-document-library/…
    – James K
    Jun 3 at 8:34
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    I’m voting to close this question because it is a simple misspelling. Also the term is a specialist one, not something that is likely to be part of learning English. Not a term likely to be understood by general English speakers.
    – James K
    Jun 3 at 8:36
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    Thank you, I just edited the question
    – user136873
    Jun 3 at 8:36
  • Probably the best thing to do is to go and ask @ThomasBilach what they mean by "causal estimand"
    – James K
    Jun 3 at 8:58
  • Notice that the word in your quote is "causal", but your original question asked about "casual". The spellings are similar, and they're often confused in writing, but these are very different words. "causual" isn't a correct spelling of either. It's not clear whether you failed to notice that these are two different words. Otherwise, as mentioned in other comments, this is a fairly specialist technical term.
    – Steve
    Jun 3 at 9:01

About the word "estimand":

Wiktionary estimand

[Etymology Apparently of mid-20th century coinage from Latin aestimandum, gerundive of aestimo (“I value", "I estimate”). Noun]
estimand (plural estimands)
(statistics) that which is being estimated.
[definition edited for format]

Some words ending in -and and -end have the same sense as this one - they denote something that receives the action of the preceding verb form, or something that should receive it.
Some examples: multiplicand, addend, augend, solvend, adherend, dividend...

Whether it's -and or -end depends on the class of Latin verb it is derived from.

As for the collocation causal estimand, it seems to mean an estimate of the degree of causality in a relation.
Google Books shows the term in multiple uses:
Google Books causal estimand
Two of the book titles are "Causal Inference" and "Statistics and Causality".

While this isn't an early English learner's term, the information about the use of the -and and -end endings may be of interest. Note, though, that most English words that end with these letters aren't examples of the same usage.