Final Answer:
In an experiment, we typically set alpha before conducting the experiment. Option A is answer.
Step-by-step explanation:
Alpha, often denoted as α, is the significance level chosen for a hypothesis test. It represents the probability of rejecting a true null hypothesis. Researchers set the significance level before conducting the experiment to define the threshold for statistical significance.
The common practice is to choose a specific alpha level (e.g., 0.05 or 0.01) based on the desired balance between Type I and Type II errors. Once the alpha level is set, researchers collect data during the experiment, analyze it, and determine whether the results are statistically significant based on the predefined alpha. Setting alpha beforehand ensures transparency and reduces the risk of biased interpretations during the analysis phase.
Therefore, the correct answer is Option A: Before.