The article "Oxytocin-gaze positive loop and the coevolution of human-dog bonds" (Nagasawa et al., 2015) describes a study in which oxytocin levels (in picograms per milligram, pg/mg) are measured in 22 dog owners before and after a 30-minute interaction with their dogs. (Oxytocin is a hormone known to play a role in parent-child bonding and is often referred to as the "love" hormone.) The difference in oxytocin level (after minus before) was calculated for each of the 22 dog owners. Approximate values based on a graph in the paper were d-bar = 27 and s_D= 30 pg/mg. Do the data from this study provide convincing evidence that there is an increase in oxytocin level in dog owners after 30 minutes of interacting with their dogs? Perform a paired-samplesttest with = .05.

• What is the explanatory variable and its levels?
• What is the response variable?
• Should the test be one-tailed or two-tailed?
• Using symbols, state the null and alternative hypothesis.
• Sketch the appropriate distribution and indicate the critical region for = .05.
• Calculate the appropriatetstatistic and show your work.
• What decision should be made about the null hypothesis?
• Compute Cohen's d to measure the size of the effect.
• Determine the 95% confidence interval for estimating the true mean of difference scores. (2 points)
• Do the results indicate a significant increase in oxytocin levels?