## 4 Discussion  
The assessment of CVA is an assessment that is routinely performed in the clinic. This assessment is added to other musculoskeletal assessments, such as pain assessment and self-perception of disability. Specifically, CVA helps therapists detect FHP and develop therapeutic strategies for its treatment. The aim of the present study was to evaluate the validity and reliability of the CVA-CVapp by obtaining a strong correlation between the Kinovea web tool and the CVA-CVapp and achieving excellent test-retest and inter-rater confidence values. The CVA has been evaluated and validated with multiple tools, although the tendency seems to be a tool that is used directly during the session. The results of the present study showed excellent test-retest and inter-rater reliability for the CV-based smartphone application. These results are similar to those shown by photometry with excellent test-retest (ICC = 0.91) and good inter-rater (ICC = 0.75) reliability [38] in healthy controls and in those with neck pain with excellent test-retest (ICC = 0.90) and inter-rater (ICC = 0.92) \begin{table}
\begin{tabular}{c c c c} \hline  & **CVA Kinovea** & **CVA-CVapp** & **Pearson’s Correlation** \\  & **Mean (SD)** & **Mean (SD)** & **Coefficient** \\ \hline Whole sample & 53.71 (6.39) & 54.63 (6.48) & r = 0.94 \\ \hline CVA, Cranivertebral angle. & & & \(p<0.001\) \\ \hline \end{tabular}
\end{table} 
Table 4: [PERSON]’s r value between the Kinovea web tool and the CVA-CVapp. \begin{table}
\begin{tabular}{c c c c c} \hline  & **Examiner** &
\begin{tabular}{c} **CVA-CVapp** \\ **Mean (SD)** \\ \end{tabular} & **ICC (95\% CI)** & **SEM** & **MDC** \\ \hline Healthy & 1 & 54.65 (7.00) & 0.90 (0.73–0.97) & 2.21 & 6.12 \\ control & 2 & 54.13 (6.09) & & & \\ \hline Neck pain & 1 & 57.67 (5.72) & 0.86 (0.61–0.95) & 2.14 & 5.93 \\  & 2 & 57.30 (5.56) & & & \\ \hline Tension type & 1 & 51.55 (5.53) & & & \\ headache & 2 & 51.17 (6.40) & & & \\ \hline Whole & 1 & 54.63 (6.48) & & & \\ sample & 2 & 54.20 (6.40) & & & \\ \hline \end{tabular}
\end{table} 
Table 3: Inter-rater reliability for subgroups and the whole sample. Figure 2: Bland–Altman plot. reliability [15]. Other manual tools, such as the \"modified head posture spinal curvature instrument\", also obtained excellent test-retest reliability values, with an ICC = 0.87 (CI 95%, 0.82-0.91) [39]. [PERSON] et al. [23] validated the FHPapp (Pyeongtaek, South Korea) mobile manual application. These authors used a smartphone application to perform measurements; the major difference between the FHPapp and the CVA-CVapp is how they are used. To measure the FHP with the FHPapp, a photo must be taken, and then the physiotherapist places three markers onto the photo (at the tragus of the ear, at C7, and at a horizontal line parallel to the ground through these marks) to obtain the CVA. With the CVA-CVapp, the CVA angle is analyzed more automatically the physiotherapist places two marks on the tragus of the ear and, at C7, a photo is taken of them, and the application automatically determines the CVA. The mean CVA observed in this study is similar to that found in other studies with higher samples [15; 18; 40; 41]. In our case, a global evaluation of all the subjects and by subgroups was developed, observing that the subjects with TTH have a lower angle and an increased FHP compared with the rest of the subgroups; this finding adds to the evidence already existing where previously it had been described that subjects with TTH tend to present an increased FHP [13]. The values of SEM and MDC obtained by the CVA-CVapp are similar to those presented by [PERSON] et al. [23]. When an instrument is used to carry out an assessment, it must consider how much the measured variable can change over time; the measurement error must be as small as possible, and in this context, SEM indicates the level of agreement between repeated measurements [42]. When the SEM is less than 7%, it is an indicator of good reliability, like the one obtained with the CVA-CV app.