Which element of an experimental study is described as the procedures applied to each subject?

In the design of experiments, "treatments" are the different procedures, conditions, or levels of a factor that are applied to the experimental units (the subjects of the study). The goal is to measure and compare the effects of these different treatments on a response variable. For example, in a medical study, the treatments might be a new drug, a standard drug, and a placebo.

A. Responses are the outcomes or measurements recorded after a treatment has been applied to an experimental unit. They are the effect, not the cause.

B. Inputs is a general term. In experimental design, the more precise terms are "factors" or "independent variables," which are manipulated via the treatments.

D. Experimental units are the subjects (e.g., people, animals, plots of land) to which the treatments are applied.

1. Montgomery, D. C. (2017). Design and Analysis of Experiments (9th ed.). John Wiley & Sons. Chapter 1, Section 1.2, "Basic Principles," defines treatments as the set of circumstances created for the experiment in order to observe their effect on the response.

2. The Pennsylvania State University. (n.d.). STAT 502: Analysis of Variance and Design of Experiments. Eberly College of Science. In Lesson 1.2, "Terminology," a treatment is defined as "a specific combination of factor levels whose effect is to be compared with other treatments."