Chapter 9.3, Problem 45E

Torsion during hip external rotation (ER) and extension may be responsible for certain kinds of injuries in golfers and other athletes. The article “Hip Rotational Velocities During the Full Golf Swing” (J. of Sports Science and Medicine, 2009: 296–299) reported on a study in which peak ER velocity and peak IR (internal rotation) velocity (both in deg.sec⁻¹) were determined for a sample of 15 female collegiate golfers during their swings. The following data was supplied by the article’s authors

Golfer	ER	IR	cliff	Z perc
1	-130.6	-98.9	-31.7	-1.28
2	-125.1	-115.9	-9.2	-0.97
3	-51.7	-161.6	109.9	0.34
4	-179.7	-196.9	17.2	-0.73
5	-130.5	-170.7	40.2	-0.34
6	-101.0	-274.9	173.9	0.97
7	-24.4	-275.0	250.6	1.83
8	-231.1	-275.7	44.6	-0.17
9	-186.8	-214.6	27.8	-0.52
10	-58.5	-117.8	59.3	0.00
11	-219.3	-326.7	107.4	0.17
12	-113.1	-272.9	159.8	0.73
13	-244.3	-429.1	184.8	1.28
14	-184.4	-140.6	-43.8	-1.83
15	-199.2	-345.6	146.4	0.52

a. Is it plausible that the differences came from a normally distributed population?

b. The article reported that mean (± SD) = − 145.3(68.0) for ER velocity and = − 227.8(96.6) for IR velocity. Based just on this information, could a test of hypotheses about the difference between true average IR velocity and true average ER velocity be carried out? Explain.

c. The article stated that “The lead hip peak IR velocity was significantly greater than the trail hip ER velocity (p = 0.003, t value = 3.65).” (The phrasing suggests that an upper-tailed test was used.) Is that in fact the case? [Note: “p = .033” in Table 2 of the article is erroneous.]