163 9 To address possible complications that may occur after treatment for head and neck cancer, the test-retest reliability of the objective tests used to measure masticatory performance and swallowing function was investigated. This reliability was tested in chapter 3 for the masticatory performance as measured with the mixing ability test (MAT), and in chapter 4 for the swallowing function as measured with the 100 mL water swallow test (WST). Intraclass correlation coefficients (ICC) of both MAT and WST showed a good and excellent reliability (ICC=0.886 and ICC=0.923, respectively). The smallest detectable changes (SDC) and standard errors of measurement (SEM) were calculated for use in the upcoming studies. In chapter 5, the associations of the MAT, WST and a salivary flow test were tested against the patient-reported outcome measures (PROMs) of the European Organization for Research and Treatment of Cancer Quality of Life core Questionnaire, Head and Neck module (EORTC QLQ-H&N35), the Swallow Quality of Life questionnaire (SWAL-QOL), and the Groningen Radiation-Induced Xerostomia (GRIX) questionnaire. In this chapter, it was concluded that the objective tests and PROs measure different constructs and can therefore not be interchanged, but should be used separately to determine objective and patientreported function.1 To predict the burden of complications and their impact on quality of life, it is important to use both objective functioning tests and patient-reported outcomes, because objective information obtained from measurements may be different from a patient’s perspective. The next step and goal of this PhD project was to create models that assess the risk of developing complications regarding mastication, swallowing and salivary flow. Publications on risk models for complications after treatment for HNC most often discuss only one type of complication, after one specific type of treatment. In addition, the majority only uses patient-reported outcomes or objective measurements, but not both.2-7 This led to the development of the associative models in chapter 6 and 7, in which factors are shown that have a negative impact on objective masticatory performance and swallowing function, respectively. Besides the models based on objective tests, it was also important to create models based on PROs. In this way, differences between the different factors found in these models can be investigated. Therefore, in chapter 8, the outcomes of the SWAL-QOL questionnaire are shown. Because different factors have an effect on objective tests and questionnaires, this highlights the additive value that these tests can have in combination with PROs in order to create the total picture of a patient, and to predict which patients are at risk to develop problems after treatment.