Keays et al. (2003) conducted a correlational study to determine "the relationship between muscle strength and functional stability in 31 patients pre- and postoperatively, following a unilateral anterior cruciate ligament rupture" (Keays et al., 2003, p. 231). The results of the study showed a significant positive correlation between quadriceps strength indices and functional stability, both before and after surgery. No significant relationship was demonstrated between hamstring strength indices 60°/s and functional stability, as presented in Table 5.
Relevant Study Results
"Patients with an unstable knee as a result of an anterior cruciate ligament (ACL) rupture rely heavily on muscle function around the joint to maintain dynamic stability during functional activity. It is uncertain which muscles play the decisive role in functional stability or exactly which aspect of muscle function is most critical" (Keays et al., 2003, p. 231). "The aim of this study was to assess the relationship between muscle strength and functional stability of 31 patients pre- and postoperatively, following unilateral ACL ligament rupture" (Keays et al., 2003, p. 231). "To assess the relationship between maximum isokinetic strength and functional performance Pearson's correlations (r) were computed. ... Due to the number of correlations computed, and therefore the increased likelihood that chance results may be evident, a more conservative significance level of α = 0.01 was adopted to control for increased Type 1 error" (see Table 5; Keays et al., 2003, pp. 232-3).
TABLE 5 Pearson's Product-Moment Correlation between Strength Indices and Function after Surgery n
Quadriceps Strength Index 60°/s
Hamstring Strength Index 60°/s
Quadriceps Strength Index 120°/s
Hamstring Strength Index 20°/s
Hop index
1. What is the r value for the relationship between Hamstring strength index 60°/s and the Shuttle run test? Is this r value significant? Provide a rationale for your answer.
2. Consider r = 1.00 and r = -1.00. Which r value is stronger? Provide a rationale for your answer.
3. Describe the direction of the relationship between the Hamstring strength index 60°/s and the Shuttle run test.
4. Without using numbers, describe the relationship between the Hamstring strength index 120°/s and the Triple hop index.
5. Which variable has the weakest relationship with the Quadriceps strength index 120°/s? Provide a rationale for your answer.
6. Which of the following sets of variables has the strongest relationship?
a. Hamstring strength index 120°/s and the Hop index
b. Quadriceps strength index 60°/s and the Carioca test
c. Quadriceps strength index 120°/s and the Side step test
d. Quadriceps strength index 60°/s and the Triple hop index
7. In Table 5, two r values are reported as r = -0.498 and r = -0.528. Describe each r value in words, indicating which would be more statistically significant, and provide a rationale for your answer.
8. The researchers stated that the study showed a positive, significant correlation between Quadriceps strength indices and pre- and postoperative functional stability. Considering the data presented in the Table 5, do you agree with their statement? Provide a rationale for your answer.
9. The researchers stated that no significant relationship could be described between Hamstring strength indices 60°/s and functional stability. Given the data in Table 5, explain why not.
10. Consider the relationship reported for the Quadriceps strength index 120°/s and the Hop index (r = 0.744**, p = 0.000). What do these r and p values indicate related to statistical significance and clinical importance?