Cancer and cancer treatment can have a deleterious impact on cognition. Only in the past 10–15 years have clinical researchers examined and documented this phenomenon in any rigorous way (8
). However, chemotherapy-associated cognitive decline and the mechanisms underlying this phenomenon are not yet well understood. A valid PCF measurement tool can assist clinicians communicating with their patients about their cognitive concerns and can serve as a useful screening tool to identify patients who may benefit from a referral for a more comprehensive neuropsychological test. Towards this end, it is crucial to understand the dimensionality of PCF in order to determine whether it is appropriate to report a single summary score or multiple scores tapping relevant content areas separately (39
). Based on evidence from internal consistency statistics, confirmatory factor analytic techniques (including bi-factor analysis) and a negligible correlation between cognitive capability
and cognitive deficiency
items, we conclude that these sets of items are perceived by cancer patients as distinct factors and their scores should be reported separately.
Results of this study were somewhat unexpected. Positively-worded (i.e., cognitive capability
) items were initially added to an earlier version to the FACT-Cog to minimize a ceiling effect – a common practice in test/scale construction. Our experiences in other health-related quality of life measures have shown that such a strategy is valid, at times. For example, we have shown that vitality or energy items (i.e., positively-worded “fatigue” items) tap the same construct as fatigue items; the added energy items appeared to cover the higher end (i.e., less fatigue) of the symptom continuum (47
). On the other hand, negatively-worded illness impact items did not seem to measure the same construct as positively-worded illness impact items. In fact, similar to our present findings, the relationship between positive and negative illness impact items was found to be orthogonal (48
). We reasoned that our findings in perceived cognitive function and illness impact, unlike cancer-related fatigue, may share similarities to the measurement of affect, where positive and negative aspects are essentially independent (49
). We therefore conclude that there are two relatively unrelated concepts that comprise perceived cognitive function: deficiency
, defined as perceived cognitive deficits and the consequences of those difficulties, and capability
, including items that tap self-efficacy and confidence. At this time, we cannot completely rule out the possibility that method variance captured by the local factors define the distinction we have made between cognitive capability
and cognitive deficiency
items, and so results from the present analyses require replication.
Previous research has suggested that depression and anxiety may have strong associations with subjective memory difficulties. Neuropsychological test performance may not be associated with patient-reported cognition after controlling for the impact of emotional distress (28
). In this study, for those with available data, we found an association between the cognitive deficiency
scale and mood measures. Yet, similar correlations with cognitive capability
were inconsistent. It is somewhat difficult to know if the different pattern of results for cognitive deficiency
and cognitive capability
are a result of true differences in the subscales or an issue related to the different instruments used to assess emotional health symptoms (e.g., EWB subscale of FACT-G vs. MCS of SF-36). The implementation of initiatives such as NIH PROMIS may help to standardize such assessments, making such comparisons more straightforward. Nonetheless, it is possible that PCF may reflect emotional distress more than cognitive dysfunction, as measured by performance-based measures.
Nonetheless, we feel that PCF is an important patient-reported outcome in its own right. Of note, even when mood symptoms were associated with the PCF subscale, the shared variance between the two concepts was not substantial. Our PCF measure is assessing something above and beyond symptom distress and taps concerns of importance to cancer patients. Some evidence suggests that PCF instruments may be associated with brain changes detectable using structural or functional neuroimagery (23
). In addition to the study conducted by Saykin and colleagues (26
) as mentioned earlier, de Groot et al. (25
) found that cognitive complaints (i.e., cognitive deficiency)
preceded measurable cognitive dysfunction or even dementia. A dose-dependent pattern was suggested: at the low end of the white matter lesions (WML) severity distribution are subjects without reported cognitive deficiency
and good cognitive performance, followed by those with reported cognitive deficiency
but without cognitive dysfunction on neuropsychological testing, and finally those with reported cognitive deficiency
progression during the last five years and measurable cognitive dysfunction. Cognitive deficiency
might be an early warning sign related to progression of WML and imminent cognitive decline. While the results from Saykin et al. and de Groot et al. are compelling, we do not claim that PCF is a superior measure of cognition than neuropsychological tests, but PCF may hold promise, in specific circumstances, as a marker of structural or functional changes in the brain.
A psychometrically sound PCF scale will assist in our understanding of how patients’ self-reported cognition relates to objective performance and to other important correlates, such as emotional distress. For the present samples, we did not have information on patient’s objective neuropsychological test performance to compare with PCF scores. However, to help elucidate this important issue we plan to apply a multi-trait, multi-method approach (52
) to explore the construct validity of PCF with longitudinal data currently being collected. Such a systematic approach will aid in our understanding of what we are measuring when we ask patients about their cognitive functioning.
A few other questions remain unanswered. Patients did not differ with respect to their scores on the cognitive deficiency items based on sex, education, or IQ. However, females and college-educated patients had better cognitive capability scores than the comparison groups. Interestingly, for those patients with IQ estimates, there were no differences between groups on cognitive capability items. The underlying reason for these group differences is not yet clear. To our knowledge, there are no published reports documenting gender difference and education effects on perceived cognitive capability. Future studies should be conducted to further understand potential mediating or moderating factors influencing perceived cognitive function (both deficiency and capability).
Although additional research is necessary to better understand what is being measured by cognitive capability items, there are some interesting potential applications for this sub-domain of PCF items. For example, it may be the case that cognitive capability items are more responsive to cognitive improvement (e.g., post-chemotherapy), compared to deficiency items, which may be more responsive to cognitive injuries. If so, capability and deficiency items could serve as complementary, but distinguishable indexes of change. Divergent and convergent validity studies using both classes of PCF items may help gauge the degree to which these items tap distinguishable concepts.
The current sample was well-educated, with nearly 60% having at least a college degree. Participants with more educational attainment scored better on cognitive capability
items while no significant differences were found between patients with different levels of FSIQ scores. It is unclear what it is about education attainment that influences patients’ perceptions. Future studies that recruit individuals with a greater range in education level are needed to better address such issues. We also note that perceived cognitive function scores are not normally distributed; however, we do not expect that this impacted the resulting factor pattern. Skewed responses on Likert type scale items do not mean that the resulting factors must be skewed. The observed non-normality may simply be due to extremeness of the item wording, which is the central concept of the Item Response Theory models. In Item Response Theory, we prefer to include items with different degrees of endorsement in order to calibrate them on the construct being measured (in this study, perceived cognitive function) (47
Furthermore, the samples for the present analysis were restricted to patients with cancer, as there is a growing interest in cognitive decrements due to either disease itself or the treatment such as chemotherapy (i.e., chemo-brain). However, the actual item content does not reflect symptoms unique or specific to the cancer experience. Nonetheless additional studies are needed in order to cross-validate the factor structure of PCF in other populations. In addition, while the tested items were developed via individual interviews and focus groups, it is noted that these items do not yet fully cover all relevant constructs within cognition; for example, executive function and multitasking are not queried, and the number of deficiency and capability items is not balanced. Using results of this study, our team is currently working on revising the PCF item bank under the Cancer PROMIS supplement (CaPS) as mentioned earlier. We are hoping that a valid and clinically meaningful PCF measure can serve as foundation for computerized adaptive testing (CAT), which can provide brief yet precise assessments in busy clinics. Routine CAT-based PCF assessment holds promise as an efficient screening tool for patients at risk for developing cognitive dysfunction.
In conclusion, this paper examined dimensionality of perceived cognitive function in cancer patients, and based on the convergence of several analyses we concluded that perceived cognitive deficiency and capability are two distinct concepts and should be scored separately. The establishment of sufficient dimensionality is an initial step towards further understanding PCF. Such an understanding holds the promise for the development of better screening tools.