Acta Pñdiatr 93: 830±835. 2004

A comparison of Likert scale and visual analogue scales as response options in children’s questionnaires H van Laerhoven, HJ van der Zaag-Loonen and BHF Derkx Emma Children’s Hospital, Academic Medical Centre (AMC), University of Amsterdam, Amsterdam, The Netherlands

Laerhoven H, van der Zaag-Loonen HJ, Derkx BHF. A comparison of Likert scale and visual analogue scales as response options in children’s questionnaires. Acta Pædiatr 2004; 93: 830–835. Stockholm. ISSN 0803-5253 Aim: To examine which response options children prefer and which they find easiest to use, and to study the relative reliability of the different response options. Methods: A consecutive group of unselected children (n = 120) filled out three questionnaires in a paediatric outpatient clinic. Each questionnaire included seven similar questions, but had different response options: the Likert scale, the Visual Analogue Scale (VAS) and the numeric VAS. In general, the questions were not related to the children’s particular diseases, but dealt with the frequency of simple activities, their feelings and opinions. The pages with the three different response options were offered in random order. Afterwards, the children rated their preference and ease of use of the different response options on a scale from one to 10. Results: Children preferred the Likert scale (median mark 9.0) over the numeric VAS (median mark 8.0) and the simple VAS (median 6.0). They considered the Likert scale easiest to fill out (median mark 10 vs 9 and 7.5 for the numeric and simple VAS, respectively). Results of the different response options correlated strongly with each other (rho = 0.67– 0.90, p < 0.05). Conclusion: Children prefer the Likert scale over the numeric and simple VAS and find it easiest to complete. The Likert scale, the simple VAS and the numeric VAS are of comparable reliability. The Likert scale is recommended for use in questionnaires for children, although research into larger and more diverse samples is needed. Key words: Children, methodology, questionnaires, rating scales, response options HHF Derkx, PO Box 22660, 1100 DD Amsterdam, The Netherlands (Tel. ‡31 20 5669111, fax. ‡31 20 6917735, e-mail. [email protected])

There is an increasing interest in measuring emotional states and quality of life of children, both in clinical practice as well as in empirical research (1). For these measurements, questionnaires including several types of response options can be used. Of these response options, the Likert scale (verbal categorical response options), the simple Visual Analogue Scale (VAS) (line response option) and the numeric VAS (numeric response option) are used most frequently. Little is known about children’s preference for response options; most research focuses on questionnaires designed for adults. The aim of this study is to examine which of the three response options (Likert scale, simple VAS and numeric VAS) is preferred and which is easiest to use by children in different age groups. In questionnaires designed for adults, both the Likert scale and the VAS are applied, most often to quantify pain severity. They have proven to be convenient and valid quantification instruments (2–6). For the assessment of other outcomes, such as quality of life, the Likert response option is most often applied because of the few cognitive demands it places on respondents (easy to complete) and because it makes easy score  2004 Taylor & Francis. ISSN 0803-5253

computation possible for the investigator (6–10). Most authors agree that there are few differences in reliability and responsiveness between the response options, and they prefer the Likert scale because it is easy to interpret (2, 4–6, 8, 9, 11). However, research into adults cannot simply be transposed to the paediatric population, since children have different cognitive capacities. Generally, children from the age of 8 y onwards are believed to be able to provide reliable reports on their well being (12, 13). Some authors favour a standardized reading test instead of an age limit to establish the minimum skills required to complete questionnaires (13, 14). Although there is little empirical evidence to show the adeptness of children of different ages to choose between the different response options, the Likert response option is most often used in paediatric questionnaires (1). March et al. (15) found that younger children and children with poorer reading skills were less able to respond to negative items on questionnaires, the effect of which biased the interpretation of the children’s responses. As for the research on severity of pain in children, the VAS is considered to be the best response DOI 10.1080/08035250410026572

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option. It does not force the respondent into fixed categories as does the Likert scale (16). Abu-Saad et al. (17) described in their research on pain experience in 355 children that the VAS has proven to be easy, effective and sensitive. Rebok et al. (13) also found that children, regardless of age, preferred circled response options to the VAS line in pain research, but because of the small study sample this conclusion is tentative (13). Theoretically, younger children who have less reading potential may be expected to prefer the VAS response option, because it requires less reading time and skills than the Likert type of response options. We studied the preference and ease of completing response options (Likert scale, simple VAS and numeric VAS), and used the correlation as a measure of relative reliability. We hypothesized, based on the literature and theory available, that younger children would prefer the VAS, whereas older children would prefer the Likerttype response option. In accordance with the studies into adult response options, we expected that the correlation between the different types of response options would be good.

Methods A consecutive group of 120 unselected children between 6 and 18 y old completed a survey containing three similar questionnaires with different response options. The survey was carried out during the children’s visit to a paediatric outpatient clinic and prior to consultation. Data registered concerned age, sex, type of school the children attended and ethnic background, as well as the time needed to complete the questionnaires. Ethnic background was defined as immigrants (first, second or third degree non-native children) and native Dutch children. Each questionnaire contained a different response scale: a five-point Likert scale (Fig. 1a), a simple VAS (Fig. 1b) and a numeric VAS (Fig. 1c). The simple VAS was a 10-cm line with the extreme answers of the Likert scale marking the ends. The children were asked to mark the line with a cross somewhere between both extremes that best reflected their answer. The numeric VAS consisted of a series of numbers from one to 10 reflecting the answering options, with again the extreme answers of the Likert scale at the beginning and the end of the series. The pages were presented to the children in random order. The children, who completed the questionnaires by themselves, were told that the same seven questions would be asked on three different pages. The investigator prevented the children from “peeking” at their previous answers and recorded time of completion. The seven-item questionnaire covered three domains: frequency of simple activities (watching television, using the bus), feelings (about dreams and current

Response options in children’s questionnaires

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mood) and opinions (about school, sports and height) (Fig. 1a, b and c). Afterwards, children were asked to rate how much they liked each answering option and how difficult they considered it to be answered, by giving them a mark from one (less preferred or most difficult) to 10 (most preferred or easiest).

Statistical analysis To assess the influence of age on preference for response options, data were analysed in two subgroups: children 6 to 12 y old and children 13 to 18 y old. Differences between the two age groups relating to preference and difficulty of the response options were tested with non-parametric procedures (Mann-Whitney U-test). Differences in time needed for completion were also tested with the Mann-Whitney U-test. Marks given for preference and difficulty of each response option were treated as ordinal data. Therefore, median scores were calculated and non-parametric procedures were used. Differences in median preference and difficulty scores within patients for the three response options were compared using the Wilcoxon statistic for paired ordinal variables. Differences in preference and difficulty between genders and between immigrants and native children were analysed using the Mann-Whitney U-test. The reliability of each response option could not be established in this study as it is of cross-sectional nature. Instead, we chose to analyse the relative reliability of the three response options by computing Spearman rank order correlation coefficients between the various response options. The assumption was that at least one of the response options would best represent the “true” answer of each child. Therefore, a high correlation coefficient would represent high reliability of all three response options; likewise a low correlation coefficient would indicate that one (or two) response options were less reliable. To discover the potential systematic biases in the location of the answers (e.g. the outer answer options on the VAS line), we compared the percentage of children scoring in each category of the five-point Likert scale with the percentage of children scoring in five categories of the VAS. In case of absence of systematic bias, these percentages would have to be comparable. We therefore categorized the numeric VAS score range of 1–10 into five even categories (scores 1 and 2 into category 1, 3 and 4 into category 2, etc.). Similarly, the line of the simple VAS was divided into five equal parts. Wilcoxon’s rank statistic for paired ordinal data was used to test whether the number of children scoring in each category was consistent across response options. A conventional significance level of p < 0.05 was chosen.

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Fig. 1.

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Response options in children’s questionnaires

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Table 1. Median marks for different response options.

Ease Preference

Likert scale simple VAS numeric VAS Likert scale simple VAS numeric VAS

Median mark

Age group 6–12 y

Age group 13–18 y

Mann-Whitney U-teste p-value

10.0a 7.5b 9.0 9.0c 6.0d 8.0

9.1 7.3 8.1 8.5 6.2 7.6

9.2 7.2 8.0 8.3 6.2 7.6

0.10 0.89 0.68 0.21 0.81 0.61

Higher than the mark for the simple VAS (p < 0.001) and numeric VAS (p = 0.005). Lower than the mark for the numeric VAS (p < 0.001). c Higher than the mark for the simple VAS (p < 0.001) and numeric VAS (p < 0.001). d Lower than the mark for the numeric VAS (p < 0.001). e Differences in median marks for the three response options between the two age groups (children 6–12 and 13–18 y old). a

b

Results One hundred and twenty-two consecutive children were asked to participate. Two refused. This resulted in a response rate of 99%. Sixty-nine children (58%) were aged between 6 and 12 y, and 51 children (42%) were aged between 13 and 18 y; 57 children (48%) were boys and 53 children (44%) were immigrants. There were more instances of missed questions on the simple and the numeric VAS than on the Likert scale (3%, 2% and 0.5%, respectively). The questionnaires were completed in 2 to 22 min, where 75% of children needed between 5 and 10 min (mean 7.8 min). Younger children needed more time to complete the questionnaire: 8.5 min vs 7.0 m, respectively (p = 0.02). Immigrant children needed more time to complete the questionnaires: 8.8 min vs 7.2 min for native children (p = 0.05). Table 1 shows the median marks for preference and difficulty of the different response options. The Likert scale scored significantly higher on both preference and difficulty, followed by the numeric VAS and the VAS (all p-values