1. “Narwhals who eat lots of halibut have longer tusks than narwhals who don’t eat much halibut.”

1A. State the three causal model types that can explain the correlation. Use X, Y, and Z in your answer. Number them 1, 2, and 3.

1B. For each of the causal models 1, 2, and 3 that you listed above, write a complete sentence, describing the causal model using words from the quoted sentence rather than using X’s and Y’s).

1C. Describe a specific third factor that might explain the correlation and how could it explain it? (it’s ok if you already mentioned it above)

2. For each of the two possibilities for the null hypothesis (it is true or it is false), there are two possible outcomes for a statistical test, yielding four possibilities in total (see the first pre-recorded video of Modules:Wk 9).

List four terms for these four possibilities

3. To get a ticket for that festival, you must test negative on a COVID test.

3A. Does the sentence mean that something is necessary to get a ticket for that festival? If so, what?

3B. Does the sentence imply something is sufficient to get a ticket for that festival? If so, what?

4. Marriage Makes You Happy

The secret to happiness is assessed by a recent study. A team of researchers analyzed data from over 300,000 people to uncover the keys to happiness across the human life span. Interestingly, they found being married to be a stronger predictor of happiness than whether someone was having sex regularly. “For all measures and regions, married people had higher subjective well-being than unmarried people,” state the researchers. “The effects were larger than for having regular sex.”

4A Describe the causal model the above passage suggests in a complete sentence using wors from the passage (no “X”s or “Y”s or “Z”s).

4B. Is the study likely to be an experiment or an observational study? Why?

4C. Using words from the passage rather than “X” and “Y”, describe an alternative causal model that could plausibly explain the finding.