Interview-based versus self-reported anal incontinence using St Mark's incontinence score

St Mark's incontinence score (SMIS) was originally designed and validated for use in an interview setting (iSMIS), and there is conflicting evidence for the validity of the self-administered SMIS (sSMIS). Our objective was to compare self-administered and interview-based reports of anal incontinence (AI) symptoms.

A total of 147 women reported symptoms of AI on a sSMIS before inclusion in a clinical study investigating the effect of conservative treatment for AI 1 year after delivery. After clinical investigations, an iSMIS was completed by one of two consultant surgeons blinded to the sSMIS results. The correlation and agreement among the individual items of the iSMIS and the sSMIS were assessed using Spearman's rho and weighted kappa statistics, respectively.

The mean iSMIS and sSMIS reported was 4.0 (SD: 3.6) and 4.3 (SD: 4.0), respectively. Spearman's rho showed a strong relationship between the two total SMIS scores (r = 0.769, n = 147, p < 0.001), and explained variance was 59% (r²=0.591). Except for the individual item about gas incontinence, women reported more frequent AI symptoms on the sSMIS than on the iSMIS. The assessment of consistency among the individual items of the iSMIS and sSMIS showed substantial agreement (κ ≥ 0.60) for all items except for fair agreement for the item about formed stool incontinence (κ = 0.22), and moderate for the item about any change in lifestyle (κ = 0.5).

The level of consistency between the two methods of reporting anal incontinence symptoms suggests that the St Mark's score may be used as both an interview-based and a self-administered incontinence score.