Item generation
Our literature search retrieved 64 studies on HRQoL in PHPT; of these, 16 were selected for analysis of the most relevant items related to the impact of PHPT on daily life. The rest of studies were excluded because they were comparative studies of pharmacological treatments or because the measures used to evaluate HRQoL were not clear. Twenty-two items were chosen, including weakness, anxiety, depression, insomnia, apathy, lack of concentration, pain (muscle, bone, and joints), mood swings, loss of appetite, and digestive problems (vomiting, nausea). The different items were assigned to the following HRQoL domains: physical, emotional, social functioning, daily activities, symptoms, cognitive function, perceived health, sexual function, energy/vitality, and pain.
Item reduction
The PHPQoL-V.1 ( see ‘PHPQoL-V.1 (PHPQoL-34) subsection) was presented to a group of 67 PHPT patients (Table
1). Their mean (± SD) age was 59.2 (±13.4) years, 69.7% were women and 52.3% had a history of surgery for PHPT.
Table 1
Sociodemographic and clinical characteristics of the 67 patients who took part in the pilot studyof the PHPQoL-v.1 questionnaire
Sociodemographic characteristics
|
Mean age (years), ±s.d.
| 59.2 ± 13.4 |
Female sex, n (%) | 46 (69.7%) |
Clinical variables
|
Surgery (yes), n (%) | 31 (47.7%) |
No treatment for kidney stones, n (%) | 49 (74.2%) |
No bone fractures in the past two years, n (%) | 65 (100%)* |
The response rate was 80.9%. Most frequently unanswered items were 32, 33, and 34, all related to working life.
Internal consistency as measured by Cronbach’s alpha was 0.96 for the 34 items.
The mean normalized score obtained by the patients on the PHPQoL-V.1 was 63.2 ±19.70.
Those items not answered by over 50% of the patients (items 16, 29, 30, 31, 32, and 33 of PHPQoL-v1, see ‘PHPQoL-V.1 (PHPQoL-34) subsection) were eliminated. In total, six items were removed in this phase.
The remaining 27 items were subjected to exploratory factor analysis, which yielded two major domains explaining 51.5% of the total variance. The first domain explained 44.5% of the variance while the second domain explained 7%. All of the items that contributed to each of the domains had a factor loading of at least 0.4; item 10 (I’ve been sad’) had a similar loading on both factors but was included in the second one due to its similarity to the other items in this domain. None of the items in either of the two domains had a factor loading of less than 0.4 and were therefore not removed.
Thereafter, the Rash analysis was performed for each one of the domains. The Rasch model lists the items in relation to severity and selects the items according to adjustment to the model, redundancy, discriminant validity and content.
Following the application of Rasch analysis (Table
2), the number of items in the first domain was reduced from 12 to 11; item 6 (
I’ve had difficulty going up and down stairs) was removed as it had an infit value of over 1.4. Overlapping items were assessed by the expert group with the aim of retaining just one item per level of impact. In the case of item 1 (
I’ve felt tired or fatigued) and item 24 (
I’ve had back pain), it was decided to retain item 24 as back pain is a common problem in PHPT and is also associated with a higher incidence of hip fracture [
33,
34]. Furthermore, the content of item 1 was covered by items 3 (
I’ve felt weak) and 4 (
I’ve found it hard to walk for a long time).
Table 2
Summary of Rasch analysis results for the physical and emotional functioning domains
Physical functioning domain (factor 1) (PHPQoL-9)
|
Item no.
|
Item
|
Measure
|
Error
|
Infit
|
Outfit
|
2 | I’ve felt sleepy after getting up in the morning and it’s been hard to get going | 0.01 | 0.14 | 1.36 | 1.29 |
26 | I’ve been able to carry out my activities as normal | −0.89 | 0.15 | 1.02 | 1.29 |
27 | I’ve restricted some leisure activities because of the symptoms of the illness | −1.04 | 0.16 | 1.21 | 1.14 |
24 | I’ve had back pain | 0.72 | 0.14 | 1.19 | 1.18 |
5 | I’ve noticed that I get short of breath when I walk quickly | −0.33 | 0.15 | 1.18 | 1.06 |
25 | My bones and/or joints have ached | 1.15 | 0.015 | 1.18 | 1.06 |
28 | The illness has limited what household chores I do | −0.74 | 0.15 | 1.02 | 0.90 |
4 | I’ve found it difficult to walk for a long time | 0.25 | 0.14 | 0.88 | 0.89 |
3 | I’ve felt weak | 0.15 | 0.14 | 0.62 | 0.65 |
Emotional functioning domain (factor 2) (PHPQoL-7) |
Item no. | Item | Measure | Error | Infit | Outfit |
17 | I’ve found it hard to concentrate | −0.17 | 0.14 | 1.28 | 1.24 |
34 | I’ve noticed I find it more difficult to concentrate at work than before | −0.73 | 0.16 | 1.19 | 1.04 |
12 | I’ve slept well | −0.51 | 0.15 | 1.13 | 1.08 |
19 | I’ve been worried, not only about the illness but also its complications | 0.25 | 0.14 | 1.09 | 1.06 |
13 | I’ve woken up during the night | 0.80 | 0.14 | 0.85 | 0.90 |
8 | I’ve felt depressed | 0.15 | 0.14 | 0.84 | 0.83 |
7 | I’ve been irritable | 0.05 | 0.14 | 0.81 | 0.79 |
In the Rasch analysis of the second domain, five items were removed as they were outside the limits established for infit and outfit values. Items 7 (I’ve been irritable) and 14 (I’ve had difficulty falling asleep) overlapped and it was decided to retain item 7 as irritability had been mentioned frequently by the patients interviewed. Furthermore, sleep-related problems were already covered by items 12 and 13. Likewise, in the case of items 8 (I’ve felt depressed) and 18 (I’ve been worried when I think about the illness), it was decided to retain item 8 as the concept of worry was covered by item 19.
Item 16 was retained based on the results of the Rasch analysis but the option not applicable was added to the response categories, as the item was only applicable to patients who were working.
After applying Rasch analysis in each domain, the total number of items of the questionnaire was 16 (PHPQoL-V.2) (see ‘PHPQoL-V.2 (PHPQoL-16) subsection); 9 items corresponded to the first domain (PHPQoL-9) and 7 items to the second domain (PHPQoL-7). Based on the content of the items included in each domain, the first domain (PHPQoL-9) was labeled the physical functioning domain while the second one (PHPQoL-7) was labeled as the emotional functioning domain.
PHPQoL-V.2 (PHPQoL-16)
Over the last 4 weeks and due to calcium problems, …
1.
I've felt sleepy after getting up in the morning and it's been hard to get going
3.
I've found it hard to walk for a long time
4.
I've noticed I get short of breath when I walk quickly
6.
My bones and/or joints have ached
7.
I've found it difficult to carry out my daily activities
8.
I've restricted some of my leisure activities
9.
I've restricted what household chores I do
12.
The illness has stopped me from sleeping well
13.
I've woken up during the night
14.
I've found it hard to concentrate
15.
I've been worried, not only about the illness but also its complications
16.
I've noticed I find it more difficult to concentrate at work than before
The correlations between the mean overall score obtained on the PHPQoL-16 and on each of the domains were over 0.90 and higher than the cutoff of 0.70. The correlation between the mean scores obtained on the PHPQoL-V.1 and the PHPQoL- V.2 was 0.98 (Table
3).
Table 3
Correlation between PHPQoL-V.2 (16 items), PHPQoL-9 (physical functioning), PHPQoL-7 (emotional functioning), and PHPQoL-V.2 (34 items) (version 1 of the questionnaire)
PHPQol-9 | 0.96 | | |
P < 0.001 | | |
N = 61 | | |
PHPQoL-7 | 0.90 | 0.76 | |
P < 0.001 | P < 0.001 | |
N = 61 | N = 61 | |
PHPQoL-V.1 (34 items) | 0.98 | 0.93 | 0.91 |
P < 0.001 | P < 0.001 | P < 0.001 |
N = 55 | N = 55 | N = 55 |
Table
4 shows a summary of the most relevant results obtained for the initial 34- item (PHPQoL-V.1) and the reduced 16-item versions (PHPQoL-V.2).
Table 4
Summary of measurement properties of different versions of the PHPQoL questionnaire
No. of items | 16 | 9 | 7 | 34 |
Score distribution | Valid observation | 61 | 66 | 62 | 55 |
Mean | 58.73 | 58.08 | 59.10 | 63.2 |
SD | 21.95 | 25.49 | 20.82 | 19.70 |
25th percentile | 43.75 | 38.89 | 42.86 | 50.74 |
50th percentile | 57.81 | 55.56 | 60.71 | 66.18 |
75th percentile | 76.56 | 77.78 | 78.57 | 80.88 |
Total item correlation | | 0.45-0.81 | 0.66-0.84 | 0.57-0.77 | 0.03-0.81 |
Internal consistency (Cronbach’s alpha) | 0.92 | 0.91 | 0.82 | 0.96 |
Rasch analysis | | | | |
Person separation | 3.06 | 2.87 | 2.23 | 3.72 |
Person reliability | 0.90 | 0.89 | 0.83 | 0.93 |
There were statistically significant differences between overall scores when analyzed by gender, with women scoring lower than men (p < 0.01). We also observed worse HRQoL with increasing age, but this did not reach statistical significance (p = 0.52). There were no significant differences in scores depending on whether or not the patients had undergone surgery (p = 0.074) or had been treated for kidney stones (p = 0.23). None of the patients reported fractures in the past 2 years.
The PHPQoL-v.2 was translated by two professional (bilingual) translators with experience in translating HRQOL questionnaires; in a consensus meeting both translations were compared with each other and with the original Spanish version. This version was then independently translated back into Spanish to ascertain equivalent significance in both languages.