Estimand

An estimand is a precisely defined quantity that a statistical analysis aims to estimate. It represents the target of inference and should be specified before data collection or analysis begins. Clear identification of the estimand is crucial for ensuring that the statistical analysis is relevant and interpretable. It provides a concrete definition of what is being learned from the data.

In essence, an estimand answers the question: "What exactly am I trying to estimate?" It forces the researcher to think critically about the underlying question of interest, define the target population, and articulate the causal effects (if any) that are being investigated.

Key components of an estimand definition often include:

• Population: The group of individuals or units to which the inference applies.

• Intervention (if applicable): The treatment or exposure whose effect is being estimated.

• Outcome: The variable being measured or observed.

• Summary Measure: How the outcome variable is summarized to answer the research question (e.g., mean difference, odds ratio, survival probability).

Specifying the estimand ensures that the statistical methods used are appropriate for the research question and that the results are interpreted correctly. It also facilitates transparency and reproducibility by clearly communicating the target of inference to others. Ambiguity in the definition of the estimand can lead to misinterpretations, biased estimates, and incorrect conclusions.