# Question

It is known that if people are asked to make an estimate of something, for example, “How tall is the University chapel?” the average guess of a group of people is more accurate than an individual’s guess. Vul and Pashler (2008) wondered if the same held for multiple guesses by the same person. They asked people to make guesses about known facts. For example,

“What percentage of the world’s airports are in the United States?” Three weeks later the researchers asked the same people the same questions and averaged each person’s responses over the two sessions. They asked whether this average was more accurate than the first guess by itself.

(a) What are the null and alternative hypotheses?

(b) What would be a Type I and Type II error in this case?

(c) Would you be inclined to use a one-tailed or a two-tailed test in this case?

“What percentage of the world’s airports are in the United States?” Three weeks later the researchers asked the same people the same questions and averaged each person’s responses over the two sessions. They asked whether this average was more accurate than the first guess by itself.

(a) What are the null and alternative hypotheses?

(b) What would be a Type I and Type II error in this case?

(c) Would you be inclined to use a one-tailed or a two-tailed test in this case?

## Answer to relevant Questions

In sub-Saharan Africa, more than half of mothers lose at least one child before the child’s first birthday. Below are data on 36 countries in the region, giving country, infant mortality, per capita income (in U.S. ...Compute the correlation coefficient for the data in Exercise 9.14. Is this correlation significant, and what does it mean to say that it is (or is not) significant? What reasons might explain the finding that the amount of money that a country spends on health care is not correlated with life expectancy? In Exercise 9.1 the percentage of mothers over 40 does not appear to be important, and yet it is a risk factor in other societies. Why do you think that this might be? Using the data in Appendix D, compute the regression equation for predicting GPA from ADDSC.Post your question

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