Validity and reproducibility of the Physical Activity Scale for the Elderly (PASE) questionnaire for the measurement of the physical activity level in patients after total knee arthroplasty

Knee osteoarthritis is a frequently occurring debilitating disease which may cause joint pain, lower extremity muscle weakness and physical dysfunction in elderly men and women[1]. At the present time, the most effective surgical treatment for end-stage knee osteoarthritis is total knee arthroplasty (TKA) as it is successful in relieving pain and improving functional ability in approximately 80% of patients[1–4]. The number of TKA procedures performed in developed countries has increased by over 25% in the last decade, partly due to population aging[2, 3], with about two thirds of all TKAs performed on women[5]. As knee replacement reduces knee pain and improves physical function[2, 6], this should allow patients to increase their physical activity level (PAL). However, although TKA patients report improvements in their PAL 12 months after surgery (compared to preoperative), they still do not reach the recommended amount of physical activity[7]. On the other hand, high levels of sport and heavy labor activities have been mentioned as important risk factors for early implant failure[8]. Thus, assessment of PAL using valid and reproducible measurement tools is of particular concern for patients after TKA[9].

The doubly-labeled water method is considered to be the gold standard for measuring physical activity[10]. However, its implementation is quite complex, has considerable costs and is therefore unrealistic in a clinical setting. A more popular tool to assess the PAL is portable accelerometry, which consists of recording a person’s body motion in free-living conditions[11]. Accelerometric systems are able to provide the duration and the intensity of physical activities, as well as the associated energy expenditure. Therefore, they are often used to validate physical activity questionnaires because they measure closely-related constructs[12]. Nevertheless, the practicability of accelerometers in routine assessment of physical activity is not usual because of their cost and the need of a technician for data handling. Recall questionnaires are commonly used in large-scale trials and epidemiological studies since they are inexpensive, easy to administer, and thus more appropriate than accelerometers to estimate PAL in a clinical setting[11]. However, up to now, no questionnaire has proven to be valid and reproducible for the assessment of the PAL in patients after TKA[13].

The physical activity scale for the elderly (PASE) is a recall questionnaire that was specifically developed for people aged 65 years and older. It assesses intensity, frequency and duration of physical activities and can be self- or interviewer-administered. The advantages of the PASE questionnaire are that it takes a short time to be completed, the recall time frame is short and it especially considers low-intensity activities (light leisure and household activities) which are commonly performed by the elderly[14]. Additionally, the PASE questionnaire has recently been recognized as a promising tool for the assessment of physical activity in knee osteoarthritis patients[13]. The PASE total score has been found to be moderately correlated with direct methods for assessing PAL (doubly-labeled water and accelerometry), but also with grip strength, static balance, knee muscle strength and 6-min walking distance in patients with knee osteoarthritis and in healthy subjects[14–21]. However, to date, the validity and reproducibility of the PASE questionnaire for the assessment of physical activity in patients with TKA has never been examined.

The main aims of this study were to evaluate the validity (using accelerometer measures as criterion) and reproducibility of the PASE questionnaire in TKA patients. A special focus was devoted to sex-related differences because some of the above-cited validation studies reported better correlations between PASE total score and objectively measured PAL in men than in women[16, 17, 19].

Two patients (1 woman) were excluded from the reproducibility analyses because they were on holiday the week preceding the study, and this significantly altered their physical activity habits. No significant differences were observed for the PASE total score between the two test sessions, in both men [-10.2% (-23.8 to 47.1)] and women [-9.7% (-24.5 to 8.1)]. ICCs were 0.77 (0.53 to 0.89) and 0.58 (0.25 to 0.80) for men and women, respectively. SEM were 32% (24 to 47%) and 35% (26 to 52%) for men and women, respectively. SDC were 89% (67 to 130%) and 97% (72 to 144%) for men and women, respectively.

Validity results are shown in Table 4 and Figure 1. A moderate and significant correlation was found between the PASE total score and aPAL for men, but not for women. Low and non-significant correlations were found between low and moderate-to-high intensity activity PASE sub-scores and accelerometry-derived minutes spent in low and moderate-to-high intensity activities, respectively.

	Men (n = 25)		Women (n = 25)
	r	p-value	r	p-value
	Mean (95% CI)		Mean (95% CI)
PASE total score vs.:
aPAL (counts∙min-1)	0.45 (0.09 to 0.71)	0.01	0.06 (-0.24 to 0.36)	0.39
PASE sub-scores vs. activity intensity:
low (min∙day-1)	0.22 (-0.13 to 0.53)	0.15	-0.01 (-0.30 to 0.30)	0.48
moderate-to-high (min∙day-1)	-0.14 (-0.41 to 0.30)	0.25	0.09 (-0.29 to 0.48)	0.33

PASE, Physical Activity Scale for the Elderly; aPAL, Accelerometry derived Physical Activity Level.

The PASE total score demonstrated acceptable reliability for men but not for women and low agreement for both men and women. When compared to accelerometry measures, PASE total score had inadequate validity. The total amount of physical activity, as assessed with accelerometry, was greater in women than in men, but this was not confirmed by the PASE total scores.

There was no evidence of gender-related differences for the PASE total score, but men tended to have higher scores than women, mainly because of higher work-related activity scores. In fact, more men than women in our group of patients were still working part- or full-time. The PASE total scores of our TKA patients were comparable to those previously obtained in healthy populations[15, 16, 21] and in patients with knee pain and disability[18]. The relatively high PASE scores we observed could be explained, at least in part, by the fact that most TKA patients begin a formal exercise prescription program after surgery and usually maintain it afterwards. In contrast, Tsonga et al.[32] reported a mean PASE score of 68 in Greek women 6 months after TKA. These scores are much lower compared to our patients, likely because the group of women evaluated in this previous study was older (73 years), had a greater BMI (30 kg∙m^-2) and was recruited early after surgery compared to the patients considered in our study.

No systematic bias was found for the PASE total score between the two test sessions, despite a substantial reduction of approximately 10% from test to retest. Personality traits, social desirability and social approval were recognized to be possible sources of systematic bias[33]. Since TKA patients are encouraged by doctors and therapists to exercise, we suppose that patients in this study tended to overestimate their physical activity to attain social approval and desirability of the investigator at the first session[34]. In contrast, knowing that the PASE total score referred to the week objectively assessed by the accelerometer, patients committed to report their physical activities more precisely and truthfully at the second session. This was particularly reflected in the recreational activity sub-score which is dependent on the reported weekly frequency and daily duration, and this resulted in a significantly lower recreational activity sub-score for women.

The PASE total score showed acceptable reliability for men but not for women according to the predefined threshold proposed by Terwee et al.[12]. These findings are comparable to those obtained in previous studies investigating the reliability of PASE questionnaire in healthy and pathological elderly populations[14–16, 20] The high mean ICC of 0.91 reported by Dinger et al.[15] in a rural elderly community can be explained by a substantial difference in the study design compared to the present investigation. In fact, questionnaire administrations were separated by only 3 days and referred to the same week in the study of Dinger et al.[15], while in the current study they referred to two consecutive but different weeks. These reliability results indicate an acceptable but moderate ability of the PASE questionnaire to discriminate between male patients following TKA according to their PAL, but not between female patients.

The PASE total score demonstrated low agreement for both men and women due to the large measurement error, with SEM values similar to those recently reported in knee osteoarthritis patients[20]. The smallest detectable change represents the smallest change in the questionnaire score that can be interpreted as a “real change” above measurement error[31]. In order to detect real changes in the questionnaire score after an intervention or over time, the smallest detectable change should be smaller than the minimal clinically important change[12]. Unfortunately, the minimal PASE score change that can be considered clinically relevant in TKA patients is not known. However, the acceptability of PASE agreement results can be interpreted using the noise-to-signal ratio, which can be expressed as an effect size (change in score divided by SEM)[35]. Tsonga et al.[32] observed an increase of 18% in the PASE total score of female patients between 3 and 6 months after TKA, while an average PASE total score SEM of 34% was observed in the present study. Interpreting the signal as the change in score (18%), the noise we obtained (34%) was almost 2 times larger than the signal. Since the noise has to be smaller than the changes in score, this suggests that the PASE questionnaire has a very limited ability to distinguish measurement error from real changes. Hence, the PASE questionnaire is not suitable for longitudinal monitoring of the PAL in TKA patients of both sexes.

The PASE total score showed inadequate validity in both men and women. Indeed, although the association between the PASE total score and aPAL was significant for men, the correlation coefficients did not reach the defined threshold of r ≥ 0.50 proposed by Terwee et al.[12]. In previous studies, the correlations between the PASE total score and aPAL ranged between 0.43 and 0.52 in healthy elderly people[15, 17, 21] and was 0.30 in patients with hip osteoarthritis[20]. There is no consensus on how high correlations should be to demonstrate adequate validity[36]. Previous studies rated the PASE questionnaire to be valid with significant but lower correlations with respect to those obtained in the present study[14–16, 18, 20]. We chose to use the more conservative thresholds because the worse the measurement properties are, the higher the risk is for misclassification and biased results[20].

In line with our findings, some studies reported better validity of the PASE total score for healthy elderly men compared to their female counterparts[16, 17, 19]. This was probably associated to household-related activities, which are generally more frequently performed by women than men[16, 19]. However, such an assumption is not supported by our observations as household activity sub-scores did not differ significantly between men and women. We nevertheless acknowledge that household activities might be a potential source of misjudgment for PASE questionnaire scoring, since, contrary to recreational and work-related activities, household activities provide a fixed score without considering frequency and duration.

The PASE total score is the standard outcome for this questionnaire. However, for explorative purposes, we determined two PASE intensity sub-scores. Indeed, differentiating patients by the time spent in low and moderate-to-high intensity activities may be important for investigations focusing on the dose–response effects of physical activity. However, unfortunately, we found no significant correlations between the time spent in low or moderate-to-high intensity activities and the respective PASE sub-scores. Therefore, our results, together with those of Svege et al.[20], seem to confirm that the PASE has no ability to differentiate physical activity intensities.

The PASE total score failed to detect the gender-related differences in the total amount of physical activity reported by the accelerometer (women > men). Questionnaires have several limitations associated with recall and reporting bias; they overestimate the time spent on strenuous activities and underestimate activities lasting less than 10 min or with a level of exertion lower than brisk walking[37]. Therefore, we suppose that the mismatch between accelerometry and PASE total score lies in the ability of the PASE questionnaire to assess low intensity activities, since the reported higher aPAL of women is explained by the fact that they spent significantly more time on low intensity activities than men. Therefore, the lack of gender differences in the PASE total score further weaken its construct validity.

The main limitation of this study is the design used to evaluate the reproducibility of the PASE questionnaire. Since the physical activity level was assessed for reproducibility during two consecutive but different weeks, it cannot be ensured that TKA patients maintained the same physical activity level during this time period. The repeated assessment of the physical activity level referring to the same week would have been methodologically more appropriate. However, a time period of less than a week between two questionnaire administrations would have increased the risk of recall bias[38]. In addition, accelerometer wearing could have influenced the reproducibility results, by inducing the TKA patients to be more active during the second week. On the other side, we explicitly asked the patients to maintain their usual physical activity habits during this time period. Two patients demonstrated disparate physical activity habits between the two weeks because of holidays and were thus excluded from reproducibility analyses thereby reducing the statistical power.

The PASE questionnaire demonstrated acceptable reliability for men but not for women, and low agreement and inadequate validity for both men and women. Accordingly, our findings suggest that there are several shortcomings associated with the use of the PASE questionnaire to assess PAL in TKA patients, particularly in women. Therefore, we do not recommend the use of the PASE questionnaire for evaluating PAL in TKA patients. We advise clinicians and researchers to use wearable accelerometers as no physical activity questionnaire has proven to be valid and reproducible in this population.