# What are the meanings of “difference-in-differences” and “causal estimand”?

In one discussion, I saw the answer containing two words that I think can be used interchangeably, but I am not sure if it's the case.

I simply state in other posts that the "generalized" **difference-in-differences estimator may accommodate intermittent exposures.

Now it's important to note that the causal estimand is plausibly unbiased if we assume constant treatment effects.

So, I want to know whether difference-in-differences estimator and causal estimand have similar meanings and are they all about the coefficient of the variable $$Treatment \times Post$$ in a DiD setting?

• IMHO, these two words should be the same in any DID setting. – Knowledge-chaser Jun 5 at 3:42

• No. Ignore the variables for a moment. The parameter $\alpha_4$ attached to the product term is the causal estimand. It's something we want to estimate. Once we actually estimate it using software, then we call $\hat{\alpha}_4$ our difference-in-differences estimate. – Thomas Bilach Jun 8 at 18:22