The Tokophobia Severity Scale (TSS): measurement model, power and sample size considerations.

OBJECTIVE

To examine the measurement model of the Tokophobia Severity Scale and consider issues of statistical power and sample size from the original instrument development study.

BACKGROUND

Fear of childbirth (FoC) and tokophobia represents an area of increasing concern within perinatal mental health research and clinical practice. Existing measures of the FoC have been criticised due to either measurement inconsistencies, difficulties in scoring or practical clinical application. Attempting to address these limitations, researchers developed the Tokophobia Severity Scale (TSS). A fundamental assumption underpinning the use of the TSS is unidimensionality, however this assertion may have been based on sub-optimal sample size and approach taken to factor structure determination.

METHOD: Parallel analysis (PA), principal components analysis (PCA), exploratory factor analysis (EFA), power analysis and sample size calculation using a reconstruction of the original dataset from published summary data.

RESULTS

Following replication of the original PCA, a three-factor model was found to offer a significantly better fit to data than a unidimensional model. Power analysis suggested the original study was underpowered.

CONCLUSION

The TSS remains a promising tool but assumptions regarding its measurement model are based on an inadequate sample size. Sample sizes for a sufficiently powered study indicated.