Stability of the 13-item sense of coherence (SOC) scale: a longitudinal prospective study in women treated for breast cancer.

PURPOSES: To test the stability of the SOC scale over time and to test the stability of the latent construct in 417 breast cancer patients at the time of diagnosis, after 1 year and in a subsample (n = 80) also 2 and 3 years later.

METHODS

The 13-item SOC scale was firstly tested with mean values and ICC over time and secondly explored with cross-sectional factor analysis, separately for two time points (baseline and after 1 year), followed by a longitudinal factor analyses.

RESULTS

Our results provide support for the stability over time (ICC 0.68, effect size 0.06). The cross-sectional factor analysis revealed a modified three-factor and a second-order factor model meeting criteria for goodness of fit. The longitudinal modified second-order factor model confirmed the construct stability character of the SOC scale with an acceptable goodness-of-fit criteria; X (2)/df = 2.91; GFI = 0.87; RMSEA = 0.07; CFI = 0.84; AIC = 962.3. The proportion of variance (R (2)) was 0.42.

CONCLUSIONS

The SOC scale is stable over time when applied to women with breast cancer. The longitudinal factor analysis gives support of a stable latent construct in the second-order factor model, allowing for merging all items to one scale reflecting the theoretical construct of SOC. Measurement errors between some items challenge future studies on alternative factor structures.