Randomness condition

Every inference procedure assumes the data came from a random sample or a randomized experiment; the AP course framework calls this the randomization condition. Without it, the sampling distribution you are leaning on does not describe your data, so the p-value or interval you compute says nothing about a larger group. Random selection is what lets you generalize to a population, and random assignment is what lets you claim cause and effect. Writing "the 40 households were chosen by simple random sample from the town directory" satisfies the condition, while "the first 40 households on my street" fails it no matter how many you add.