6. Recent findings have suggested that infant sex differences exist in behavioral and physiological reactions to stress. One study evaluated changes in the heart rate for a sample of infants placed in a stressful situation. For the 15 female infants, a printout for the data from the OneSampleT 95% con- fidence interval on the change in heart rate shows the following: n Variable DF CHANGE 15 14 Sample Mean 10.70 Std. Dev. 17.70 Std. Err. 4.57 95% CI (0.90, 20.50) a) Show how the computer statistical software obtained the value for "Std. Err.". Explain what this represents. (4 marks) b) Explain how the software obtained the value of "DF", and indicate which t-score was used in constructing the 95% confidence interval. (2 marks) c) From the confidence interval shown, can you conclude that the true mean change in heart rate is positive? Explain. (2 marks) d) Explain the implications of the term "robust" regarding the normality assumption made to con- duct this analysis. (2 marks)