Abstract: Most questionnaires for somatic symptoms focus on occurrence, frequency, or severity, and in doing so, they might not be able to comprehensively assess the burden that symptoms present to patients. For example, a symptom might occur at a high frequency but only a minimal severity, so that it is less likely to be a burden on a patient; whereas a symptom that has both a high frequency and severity is more likely to be negatively impacting a patient. Study 1 examined frequency and severity scores for classic Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) symptoms among patients with ME/CFS versus a control group. Findings in Study 1 indicate there were more frequency/severity discrepancies for individuals with ME/CFS versus the control group. Study 1 concluded that collecting data on both measures of symptom burden provides unique indicators that can better assess the burden of the symptoms on patients. In a separate data set, Study 2 reported reliability data on slight differences in the time period and the way the severity was assessed. Study 2 findings indicated high levels of reliability for these changes in the time period and the way questions were asked. These studies provide important psychometric properties that could lead to more reliable and valid assessments of patients with post-viral illnesses. https://www.mdpi.com/2624-8611/5/3/42 (this is in MDPI Psych)
From the discussion, "Just as with Eskimos who can differentiate multiple varieties of snow, patients with ME/CFS can differentiate in more sophisticated ways subtle frequency and severity differences in symptoms that are not noticed among those in the non-symptomatic, healthy population." Not sure the Eskimos were needed in order to make a valid point. "Study 2 explored how respondents would respond to similar questions on the DSQ-SF and DSQ-PEM and the correlations were high, suggesting there is adequate stability in the measure. When the question was worded differently in terms of 1 versus 6 months and changing the term “bother” to “severity”, the correlation, again, was relatively high, although lower than when the questions were asked in an identical way. While it is difficult to determine whether it was the alternate time frame or alternate wording that most influenced differences in patient scores, this lower correlation may reflect differences in how patients interpret the severity of a symptom versus how much a symptom bothers them. Since scores were slightly higher when the question used “bother” rather than “severity”, this may indicate that patients believe the bothersome nature of a symptom to be greater than the actual severity of that symptom. The term bother may provide a broader view of patient impairment than severity alone, although further research is needed to better understand patients’ interpretations of these terms. Overall, the findings suggest that small changes in either the length of symptoms or using the words “bother” or “severity” does not dramatically change the outcomes." My interpretation, "we changed two variables but we are going to ignore the possible influence of one of them in order to make claims about the impact, or otherwise, of the other".... "There are several limitations in the current studies. Individuals in Study 1 were diagnosed using different case definitions, so it is probable that all patients did not meet the IOM [6] criteria. In addition to the criteria for sample selection not being homogeneous among the different datasets used in Study 1; in some groups, the patients self-reported having ME/CFS; in others, they were identified by the doctor; in others, they were members of patient associations." That is quite an important limitation.
This supports my complaint about the ICC not being "valid and reliable". There's too much leeway in what is included in a cohort. Subjects who qualify by "physical weakness" will provide different responses than subjects who qualify by "thermoregulation irregularity". Researchers who want certain conclusions could (ab)use the criteria to manipulate the outcome.
