Self-study
In an experiment, subjects were shown a series of images on a computer screen, appearing usually at the top but occasionally at the bottom. ████████ ████ █████ ██ █████ ████ ████ █████ ███ ████ █████ █████ ██████ ██ ███ ███████ ████ ███████ █████████ ████ ████ ████ ██ ███ █████ ███ ████████ ███ ████████ ████ ████ █████ █████ ███████ ██ ████████ ████ ████████ ████ ███ ██ ███ █████████ ████████ ██ ████ ███ ██████ ███████ ████ ███ ████ █████ █████ ██████ ██████ ██ ███ ████ ████ █████ ████ ████ ███████ ████ ██ ███ █████
Summary
Images shown to subjects in an experiment usually showed up at the top of the screen but sometimes showed up at the bottom.
When asked to guess where the next image would appear, the subjects were correct less than half of the time.
Their guesses were based on patterns they thought they saw.
If they always guessed that the image would show up at the top, they would guess correctly most of the time.
Notable Valid Inferences
The images showed up at the top of the screen over 50% of the time.
21.
If all of the statements █████ ███ █████ █████ ███ ██ ███ █████████ ████ ████ ██ █████
a
If the subjects ███ ██████ ███████ ████ ███ ████ █████ █████ ██████ ██ ███ ████ ████ █████ ███ ████ ████ ██████ █████ ███████ ██ ███ ███████ ████ ████████ ████ ███ ██ ███ █████████
Could be false. It could be that the strategy of always guessing that the images would be at the top came from repeatedly observing the image at the top. In the world where the subjects were always guessing top, we don’t have the information to say what this guess was based on.
b
Basing one's guesses █████ ████ ████ ██████ ████ ██ ███ █████ ██ ████████ ███ ████████ ███ ████ ██ ████ ██████ ██ ████ ██ ███████ ███████ ████ ██████ ████████ ████ ████ ███ ████████ ██████ ████ ██████ █████
Could be false. (B) compares the strategy that the subjects used (basing guesses on perceived patterns) with a strategy that is not mentioned in the stimulus, so we cannot say which of these strategies is more likely to lead to correct guesses.
c
There was no ███████████ ███████ ████ ███ █████ ██████████ ███████ ████████ ██ ███ ██████ ██ ██████ ██ ███ ████████ ███████
Could be false. It could be the case that there was a predictable pattern, but that the subjects didn’t pick up on it quickly enough to guess correctly a majority of the time.
d
Some of the ████████ █████████ ███████ ████ ███ ████ █████ █████ ██████ ██ ███ ██████ ██ ███ ████████ ███████ ███ ████ ██████████
Must be true. Since subjects guessed correctly less than half of the time but would have been right most of the time by always choosing "top," they must have sometimes guessed "bottom" and been wrong. Otherwise, their accuracy wouldn’t be below 50%.
e
The most rational ████████ ███ ████████ █████████ █████ ███ ████ █████ █████ ██████ █████ ████ ████ ██████ ██ ██████ █████ ████ ███ █████ █████ ██████ ██ ███ ████
Could be false. While we know that always guessing top would be more accurate than the strategy that the subjects used, we don’t know that always guessing top would be the most accurate strategy. There could have been other, more accurate, strategies.