Using qualitative research to facilitate the interpretation of quantitative results from a discrete choice experiment: insights from a survey in elderly ophthalmologic patients

Figures & data

Table 1 Attributes and levels included in the discrete choice experiment

Attributes	Levels
Effect on visual function	Stabilization
	Improvement
Side effects	Mild–moderate, frequent, eye-related
	Severe, rare, eye-related
	Very severe, very rare, systemic
Monitoring frequency	Monthly
	Every 2 months
	Every 4 months
Approval status	Approved for AMD
	Not approved for AMD
Injection frequency	Scheduled, monthly
	Scheduled, every 2 months
	Scheduled, every 4 months
	On demand, following monthly monitoring*

Note:

* Description used for the medical concept pro re nata.

Abbreviation: AMD, age-related macular degeneration.

Figure 1 Example of a choice task.

Table 2 Patients’ characteristics (N=86)

Age, n (%)
Younger than 45	0 (0)
46–54	2 (2)
55–64	8 (9)
65–74	33 (38)
75 years or older	43 (50)
Sex, n (%)
Female	44 (51)
Educational level, n (%)
No degree	0 (0)
Lower secondary education	66 (77)
College	6 (7)
Academic or comparable degree	14 (16)
Time since AMD diagnosis, n (%)
<1 year	8 (9)
1–5 years	60 (70)
≥6 years	18 (21)
Number of injections, n (%)
1–5	11 (13)
6–12	15 (18)
≥13	58 (69)
Missing	2
Current treatment, n (%)
Aflibercept	35 (41)
Bevacizumab	1 (1)
Ranibizumab	49 (58)
Missing	1
Affected eyes, n (%)
One	54 (63)
Both	32 (37)
Self-rated visual functioning, n (%)
Excellent	2 (2)
Good	15 (17)
Fair	47 (55)
Poor	17 (20)
Very poor	5 (6)
Self-rated general health, n (%)
Excellent	6 (7)
Good	45 (52)
Fair	29 (34)
Poor	6 (7)
Very poor	0 (0)

Abbreviations: N, total number of participants; n, number of participants in subgroups; AMD, age-related macular degeneration.

Table 3 Results from panel mixed multinomial logit model

Attributes and levels	Coefficient (95% CI)	P-value	Standard deviation (95% CI)
Effect on visual function
Stabilization	−0.22 (−0.04, −0.40)	0.0163	0.60 (0.40, 0.80)
Improvement	0.22 (0.04, 0.40)	0.0163	0.60 (0.40, 0.80)
Monitoring frequency
Every month	−0.06 (−0.30, 0.18)	0.6357
Every 2 months	0.34 (0.14, 0.53)	0.0007	0.05 (−0.37, 0.46)
Every 4 months	−0.28 (−0.49, 0.07)	0.0094	0.52 (0.25, 0.79)
Approval status
Not approved	−0.56 (−0.34, −0.78)	0.0000	0.72 (0.49, 0.95)
Approved	0.56 (0.34, 0.78)	0.0000	0.72 (0.49, 0.95)
Injection frequency
Scheduled, every month	−0.66 (−1.04, −0.28)	0.0007
Scheduled, every 2 months	0.15 (−0.09, 0.40)	0.2225	0.48 (0.11, 0.84)
Scheduled, every 4 months	−0.11 (−0.41, −0.18)	0.4446	0.84 (0.48, 1.21)
On demand, following monthly monitoring	0.62 (0.23, 1.01)	0.0019	0.88 (0.46, 1.29)
Side effects
Mild–moderate, frequent, eye-related	0.86 (0.61, 1.12)	0.0000
Severe, rare, eye-related	−0.03 (−0.20, 0.13)	0.6939	0.04 (−0.62, 0.70)
Very severe, very rare, systemic	−0.83 (−1.08, −0.58)	0.0000	0.63 (0.37, 0.89)

Notes: Number of observations =1,032 (86 respondents ×12 choice tasks). Pseudo R²: 0.18; Akaike information criterion: 1.17.

Abbreviation: CI, confidence interval.

Figure 2 Patient preference estimates.

Table 4 Examples of patients’ statements

Attributes and levels	Examples of patients’ statements given while answering choice tasks
Visual function	“I cannot imagine that it gets better with my eyes and I would be happy if it stays as it is right now. Both would be great.”
	“Of course improvement is better, but stabilization is good as well […] [looks at the other attributes].”
	“My visual function is so bad – I really need improvement – stabilization is not enough for me […].”
Injection frequency	“I prefer to come here only when it is necessary, it works well.”
	“Every month, that is how they did it before, but if I can have it only every 2 months and it works as well, then I choose every 2 months.”
	“I only want one of those injections if I really need it and my physician says so.”
Monitoring frequency	“The monitoring always takes a lot of time, increasing the time intervals would be nice, but every 4 months is too dangerous.”
	“I don’t notice the changes myself, I need these visits at least every 2 months.”
	“I really don’t want to come here every month for monitoring, but I don’t want to miss out if things get worse […] I am scared of that situation.”
Approval status	“I cannot believe this medication gives improvement if it is not approved. I’d rather choose the approved one.”
	“I would not participate in a trial, so why should I choose the non-approved drug if there is also this approved one.”
Side effects	“I had a heart attack before and I do not want to have it again. I do not want a treatment that might cause a heart attack.”
	“I have this itching after each injection, but it is gone the next day, so I don’t mind risking this.”
	“Oh no, I don’t want these very severe side effects – I am really scared of those.”