Validation of existing outcome scales
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Contents |
Methods
Subjects
Describe the subjects involved in the validation of the scale, emphasizing criteria that enhance their representativeness for the main aim of the scale. For example, if a scale is targeted at evaluating a psychological profile of researchers for a country like Brazil, then this section should emphasize that the subjects in the study are similar to the average population of researchers in Brazil as a whole.
- The subjects in the present study were outpatients and inpatients with cancer at the National Cancer Center Hospital East, Japan. Eligibility criteria included (a) 18 years or older, (b) informed of their cancer diagnosis, (c) able to complete the questionnaire and participate in a brief interview, and (d) not suffering from a severe mental or cognitive disorder. The study was approved by the Institutional Review Board and the Ethics Committee of the National Cancer Center. Written consent was obtained after each patient had been fully informed of the purpose of the study.(Okuyama, 2000)
Validity
In this section you should describe each of the concomitant scales applied to evaluate validity. Each scale description should have a list of its psychometric properties, previous studies evaluating them, and how the properties varied across different samples.
- Visual Analogue Scale (VAS) for Fatigue. To investigate the convergent validity of the CFS, we asked patients to express the intensity of the fatigue they experienced at the time on a 100-mm VAS, ranging from not fatigued at all to extremely fatigued, thus expressing a global sensation of fatigue. (Okuyama, 2000)
Test–Retest Reliability
Describe how test-reliability was performed, including the time intervals between tests. Time intervals should neither be as short to allow subjects to remember their previous responses nor too long to allow underlying construct to change. These periods will change from condition to condition.
- Ambulatory breast cancer patients who were not receiving active cancer treatment were recruited in a study to assess the test–retest reliability of the new scale. They took this survey by mail with an interval of about 8 days. In addition, ambulatory cancer patients from the Palliative Care Unit were asked to complete the questionnaire on two occasions to investigate the possibility of using the CFS over the telephone. On the first occasion, they completed the questionnaire in the outpatient clinic of the Palliative Care Unit, and on the second occasion, they were asked all of the questions in the CFS over the telephone within about 3 days of the written assessment. On the former, occasion the time required to complete the CFS was measured. (Okuyama, 2000)
Statistical Methods
Describe the methods used to conduct factor analysis, analyze test-retest reliability, internal reliability, validity, and sensitivity to change.
- The CFS was developed by factor analysis of the draft items followed by varimax rotation. This method was used to explore the underlying structure that adequately explains the overall observed variation and to reduce the complexity of the data. The number of factors was identified by the Scree test. Construct validity was evaluated based on whether repeating factor analysis reproduced the factor loading pattern that was seen in the scale development phase. Intersubscale correlations were evaluated by calculating Pearson's correlations. Convergent validity was evaluated by calculating Pearson's correlations between the CFS scores and the VAS scores. The associations between the CFS and the ECOG Performance Status, HADS, and MMS were also assessed by calculating Pearson's correlation coefficients. Reliability was evaluated by calculating Cronbach's alpha coefficient, a measure of the internal consistency of responses to a group of items. Test–retest reliability was assessed by Pearson's correlations comparing the scores reported on two separate occasions. All statistical procedures were performed using the SAS statistical software package (SAS Institute Inc., 1997). (Okuyama, 2000)
