Psychology – Statistics and Probability

What are the appropriate H0 and Ha for each of the following research studies? Note whether the hypothesis test is one- or two-tailed.
a. A study in which researchers want to test whether there is a difference in spatial ability between left- and right-handed people.
b. A study in which researchers want to test whether nurses who work 8-hour shifts deliver higher-quality work than those who work 12-hour shifts.
c. A study in which researchers want to determine whether crate-training puppies is superior to training without a crate.

Professors instructions:
As you write the null and alternative hypotheses, please use words instead of symbols. See below for examples.

1. The null hypothesis states that there is no difference between the two groups being compared. “Null and void” means that something has no value, no meaning. In statistics, null means “no difference”. As researchers, we never hypothesize the null because there is no way to find evidence for it. It is impossible to test the null hypothesis. Example: I am interested in whether students in PSY 322 do better when they use one form of textbook (electronic or paper) over another. What is the null hypothesis? The null hypothesis is “There is no difference in student performance between those who use an electronic book and those who use a hard copy”. The alternative hypothesis is, “There is a difference in the performance between students who use an e-book and those who use a hard copy.” This is an example of a two-tailed alternative hypothesis.

2. The alternative hypothesis is the hypothesis of difference. It states that there will be a difference between the two groups. One example is: “Performance in PSY 322 will differ between students who use an electronic book and students who use a hard copy”. Another example is: “Students who use a hard copy will out-perform students who use an electronic copy”. Do you see the difference between these two alternative hypotheses? One is directional (one tailed, a specific difference is predicted) and the other is non-directional (two tailed, a general difference is predicted but it is not predicted which group will be higher).

3. One-tailed means that the direction of the difference is predicted. The researcher predicts which group will score higher or better or happier or whatever the outcome variable is. “Performance in 322 will be higher for students who use a hard copy text than students who use an electronic text”. Not only is a difference predicted, but the researcher guesses which one will be high and which one will be low.

4. A two-tailed hypothesis means that the researcher does not predict which one will be high and which one will be low. The researcher only predicts that there will be a difference. “The students’ performance will differ”. The researcher doesn’t guess which one will be higher than the other.