Because a small sample of subjects contributed data to these analyses and because two observed results were anomalous (positive change for minimally improve for number of days of vomiting and nausea and negative change for minimally worsen for mean severity of nausea), a single, preliminary threshold for minimal-meaningful change is proposed rather than a range of thresholds.
Each of the nine tests of known-groups validity were statistically significant: there was a statistically higher number of days of vomiting or nausea per week, number of episodes of vomiting per week, and mean severity of nausea for subjects with vomiting/nausea as defined by the external criteria (Table 6).
Therefore, the following preliminary thresholds for meaningful worsening are suggested based upon interpolation between the 0.50 SD and one SEM: 0.90 for number of days of nausea and vomiting, 1.20 for number of vomiting episodes; and 0.40 for mean severity of nausea.
The one SEM for number of days of vomiting and nausea was 0.63, 1.35 for number of episodes of vomiting, and 0.27 for mean severity of nausea.
Consistent with expectations, mean differences for the no-change group for all three NVSA© scores were small (mean and median, respectively: 0.02 and − 0.00 for number of days of vomiting or nausea; 0.06 and 0.07 for number of vomiting episodes, and 0.00 and 0.04 for mean severity of nausea).
Preliminary thresholds for meaningful worsening were 0.90 days for number of days of vomiting or nausea per week, 1.20 for number of episodes of vomiting per week, and 0.40 for mean severity of nausea.
Ceiling effects (greatest severity of nausea and vomiting) were under minimal (according to well-accepted criteria: [34] 10.5% for number of days of vomiting or nausea, under 2.0% for number of episodes of vomiting, and under 3.5% for mean severity of nausea. Missing data rates ranged from a low of 2.5% (week 1) to to a high of 9.9% (week 2).
For mean severity of nausea, the minimally-worsened group had positive and negative change scores (mean and median of 0.16 and 0.27, respectively).
The mean and median effect size for number of vomiting episodes was 0.88 and 0.60, respectively, and the same for mean severity of nausea was 0.36 and 0.38, respectively.
The mean and median one-half SD for number of episodes of vomiting was 1.08 and 0.99, respectively, and the same for mean severity of nausea was 0.55 and 0.54, respectively.
