A Ladder interview is an interviewing technique where a seemingly simple response to a question is pushed by the interviewer in order to find subconscious motives.
It begins with a simple question, and then another question is asked about that response. For example, an interviewer may ask: "How come you skipped class?" and the response may be: "I went out with my friends". The next question would be something like "Why did you go out with your friends?". Essentially, the format is as follows:
The first responses are generally functional justifications, like "I went out with my friends because I wanted some pizza", or "I wanted some pizza because I used to eat it as a child"; but eventually the interviewer hopes to reach a virtue justification like "It's good to be childish". Then it is fair to conclude that the interviewee skipped class because he valued childishness.
This technique is used for marketing in order to see what values inspire the consumption of the particular product. A chocolate bar producer would do this test so they can match the most common terminal virtue to their product in an advertisement. For example, the virtue of justice, or a virtue of efficiency, or in the above example, the virtue of childhood.