Interviewers attempted to contact 392 patients, of which 282 were reached. Of these 282 patients, 72 agreed to participate, while 161 declined, 35 were lost to follow up, and 14 were not eligible. We conducted interviews with 72 adults with cancer. One participant was not able to complete the entire interview, resulting in a sample size of 71 for the cognitive interview portion. A sample description is provided elsewhere [2] (Appendix 4) and briefly described here. Half the sample was female (n = 36). The study sample included 12 inpatients and 60 outpatients. It was split evenly between participants with nonmetastatic (n = 34, 47.2%) and advanced/metastatic (n = 38, 52.8%) disease. Participants’ primary cancer types were diverse, including 22 different cancer types [2] (Appendix 5). Almost half of participants (n = 32, 46.5%) chose one of the standard activities (A through D). No participants used “sit on the edge of the bed.” Several patients who could walk a mile but who chose to use “the ability to walk 15 min” were primarily concerned with the word “briskly.” Chosen activities for Form X included walking for a distance not included in Form A-C (n = 7), walking briskly for distances both greater and less than 1 mile (n = 7), yardwork (n = 4), such as mowing the lawn or gardening, other forms of high- intensity exercise such as running, exercise videos, biking (n = 8), bed mobility (n = 3), going up steps (n = 2), walking without a walker, bending over to pick something up, backpacking, driving, getting dressed, lifting heavy objects, and organizing classroom. Table 1 presents the proportion of participants using each form.

At the beginning of the interview, participants were asked, “How would you describe your physical functioning currently?” and then, “When you were thinking about your physical function, how far back in time were you thinking?” The purpose was to describe participants’ “natural recall period” when considering their current PF status. The majority of participants used a recall period of more than 1 month, with 27.8% (20/72) using a natural recall period of 1–6 months, and 44.4% (32/72) using a recall period of more than 6 months. Nineteen participants (26.4%) used a recall period of less than a month, with six (8.3%) using a recall period of 1–4 weeks, six (8.3%) using a recall period of less than 1 week, and seven (9.7%) using a recall period of today (at the time of the interview) to describe their current PF. (One participant did not specify a natural recall period.)

The three most common reasons for the natural recall periods chosen by participants were related to changes since diagnosis or getting sick (15/72, 20.8%), since starting treatment (16/72, 22.2%), or since most recent surgery (15/72, 20.8%) (Table 2).

The majority of inpatients used a recall period of less than 1 week (8/12, 66.7%). Yet the majority of outpatients used a recall period of more than 1 month, with 19 of 60 (31.7%) using a recall period of 1–6 months and 31 (51.7%) using a recall period of more than 6 months. There were no apparent differences in natural recall periods for participants with advanced/metastatic cancer and nonmetastatic cancer or by treatment type.

To examine the appropriateness of a 7-day recall period, participants were asked “Is your physical functioning now different than it was a week ago?” and were prompted to expand on their answer. As a follow up, participants were asked how often their PF changed within a week. Overall, they found it easy to think back 7 days and described changes in their functioning. Over half (n = 37, 51.4%) indicated no change in PF in the past week. Nine indicated that their PF fluctuated day-by-day or multiple times per week with treatment. Seven participants indicated changes that occurred week-by-week with cycles of treatment. For seven participants, pain was the primary indicator and driver of PF over the past week. In terms of frequency of change, most indicated that their changes in PF were unpredictable due to pain. Table 3 presents illustrative quotes on how participants experience changes in their PF.

During concept elicitation, participants did not have trouble recalling their PF or describing changes in their PF over time within the 7 days prior to the interview.

The unit of analysis for this section is the number of item responses per person, with up to 9 responses per person for 71 participants (639 responses total). When participants were offered items with no recall period (items 1–4 in Appendix 3), the most frequently used recall period was more than 4 weeks (41.7%). Table 4 shows the recall period used for items with no recall period.

This table presents the recall periods participants reported across four items with no recall period. The total number of responses possible is 288 (72 participants × 4 items with no recall = 288). One participant did not complete the cognitive interview (missing all four items with no recall period) and one participant did not provide a recall period for one item.

When participants were offered a 7-day recall (items 5–9 in Appendix 3), the most frequently used recall period was 7 days (52.7%). Table 5 shows the recall period used for items with a 7-day recall period.

This table presents the recall periods participants reported using five items with 7-day recall. The total number of responses possible is 360 (72 participants × 4 items with no recall = 360). One participant did not complete the cognitive interview (missing all five items with no recall period) and two responses were missing.

Table 6 shows which recall periods were used by participants depending on treatment location. For inpatients, PF changes are precipitous due to surgery or treatment. Inpatients tended to use a recall period of 1 week or less. Outpatients used a recall period of more than 4 weeks more often than any other recall period length (48.1% of responses) when no recall period was offered. When a 7-day recall period was offered, outpatients most often used a 1-week recall period or less (67.2% of responses).

This table presents the recall periods participants reported using four items with no recall period versus five items with a 7-day recall period. The total number of possible inpatient responses for participants responding to items with no recall and 7-day recall are 48 and 60 respectively. The total number of possible outpatient responses for participants responding to items with no recall and 7-day recall period are 240 and 300 respectively. One outpatient did not complete the cognitive interview, accounting for most of the missing responses.

For items with no recall period, the most common retrieval process was thinking back to the last time an activity was tried or completed (113 responses; 40.2% responses). Figure 2 shows the most common retrieval strategies used for items with no recall period.

Common retrieval strategies for items with no recall period

For inpatients, the most common retrieval strategies were PF since their most recent surgery (50%, n = 24), since they last tried or completed an activity (31.3%, n = 15), or now (i.e., at the time of the interview) (14.6%, n = 7). For outpatients, retrieval strategies focused on PF since they last tried or completed an activity (42.1%, n = 98), now (13.3%, n = 31), since their diagnosis (10.3%, n = 24), or since their most recent surgery (9.4%, n = 22). Figure 3 shows the most common retrieval strategies for items with recall periods; using the recall given was the strategy used most often (46.3%).

Common retrieval strategies for items with 7-day recall period

For inpatients, the most frequently used retrieval strategies for items with 7-day recall were thinking of their PF since their most recent surgery (45.0%, n = 27), the recall period offered (33.3%, n = 20), or since they last tried or completed an activity (15.0%, n = 9). For the 9 inpatients that used a strategy of when they last tried the activity, all had tried the activity within 7 days since the interview. Outpatients most often thought about the recall period offered (49.0%, n = 143) or since they last tried or completed an activity (28.1%, n = 82) when retrieving responses for items with a 7-day recall period. For the participants that used the retrieval strategy of when they last tried an activity, 18/82 responses were based on reports of having tried the activity outside of the 7-day recall window.