# Table 1 Comparison of traditional and mixed-effect approaches and questions to answer when choosing a statistical method for the analysis of labour pain in repeated measures data

Questions to ask when you choose statistical method Statistical property Statistical method
End-point Analysis rANOVA Mixed effect models
1. What do you want to compare? Research question Compares mean labour pain between groups at one time-point Compares mean labour pain between groups at several time-points
Study interactions between timeatreatments
a. Compares mean labour pain between groups at several time-points
b. Study interactions between time and treatment
c. Study individual women’s pain changes over time
2. Do you have measurements of labour pain at all time-points for all women? Missing data Excludes woman with missing measurements Excludes woman with missing measurements Use all available measurements under the assumption of missing at random (MAR)
Possible effect of omitting women with missing values? Sample bias Sample bias Not applicable
Possible effect of imputation of missing data? Estimation bias Estimation bias Not applicable
3. Can you assume that correlation of pain is equal between all time-points? Assumption on the between woman pain correlation Independent Independent Independent
Are the labour pain assessments made with unequal distances, e.g. at baseline, and after 2 and 6 h? Assumption on the individual woman pain correlation or covariance matrix Independent Compound symmetry Allow a variety of covariance structures, e.g. Independence, Compound symmetry, AR [1], Unstructured
4. Can you assume that the variance of labour pain is equal at all time-points? Assumption on the variance of pain at different time-points Constrained to be equal at all time-points Constrained to be equal at all time-points Allowed to vary
5. Are measurements of labour pain normally distributed? Assumption of normal distribution Normality assumption Normality assumption Normality assumption
6. What requirements do you have on your statistical model to model the pain over time? Description of time effect Simple Flexible Flexible
7. Would you like to consider labour pain traits for individual women over time? Estimation of individual trends No No Yes
8. Do you need to adjust labour pain for factors that vary during labour, e.g. cervical dilatation and use of other pain relief? Time dependent covariates No Yes Yes
9. Do you have knowledge of applied statistics? Ease of implementation Very easy Easy Complex
10. Do you have access to a good computer? Computational complexity Low Low High