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.