Exercise reduces depressive symptoms in adults with arthritis: Evidential value

Abstract

Aim: To determine whether evidential value exists that exercise reduces depression in adults with arthritis and other rheumatic conditions.

Methods: Utilizing data derived from a prior meta-analysis of 29 randomized controlled trials comprising 2449 participants (1470 exercise, 979 control) with fibromyalgia, osteoarthritis, rheumatoid arthritis or systemic lupus erythematosus, a new method, P-curve, was utilized to assess for evidentiary worth as well as dismiss the possibility of discriminating reporting of statistically significant results regarding exercise and depression in adults with arthritis and other rheumatic conditions. Using the method of Stouffer, Z-scores were calculated to examine selective-reporting bias. An alpha (P) value < 0.05 was deemed statistically significant. In addition, average power of the tests included in P-curve, adjusted for publication bias, was calculated.

Results: Fifteen of 29 studies (51.7%) with exercise and depression results were statistically significant (P < 0.05) while none of the results were statistically significant with respect to exercise increasing depression in adults with arthritis and other rheumatic conditions. Right-skew to dismiss selective reporting was identified (Z = -5.28, P < 0.0001). In addition, the included studies did not lack evidential value (Z = 2.39, P = 0.99), nor did they lack evidential value and were P-hacked (Z = 5.28, P > 0.99). The relative frequencies of P-values were 66.7% at 0.01, 6.7% each at 0.02 and 0.03, 13.3% at 0.04 and 6.7% at 0.05. The average power of the tests included in P-curve, corrected for publication bias, was 69%. Diagnostic plot results revealed that the observed power estimate was a better fit than the alternatives.

Conclusion: Evidential value results provide additional support that exercise reduces depression in adults with arthritis and other rheumatic conditions.

Keywords: Adults; Arthritis; Bias; Exercise; Meta-analysis; Physical activity; Physical fitness; Publication bias; Rheumatic disease; Systematic review.

Figure 1. Forest plot for changes in depressive symptoms

The black squares represent the mean difference while the left and right extremes of the squares represent the corresponding 95%CIs. The middle of the black diamond represents the overall mean difference while the left and right extremes of the diamond represent the corresponding 95%CIs.

Figure 2. P-curve results for evidential value

Results are significantly right-skewed (P < 0.0001), suggesting that evidential value exists that exercise reduces depressive symptoms in adults with arthritis and other rheumatic diseases. The graphed results include 15 statistically significant P-values < 0.05. Fourteen additional results were entered but excluded from the analysis because of non-significance (P > 0.05).

Figure 3. Diagnostic plot for power estimation

This figure illustrates how close the expected P-curve is to the observed P-curve for each level of power between 5% and 99%. The y-axis is the perfect fit distance for each level of power. The estimated power for exercise-induced changes in depressive symptoms data is 69%. The solid red circle is generally lower than the other markers, suggesting that the power estimate is a better fit than the alternatives. The flatter the curve, the less confidence in the power estimate. Alternatively, a V-shape suggests an ideal estimate of power.