Testing the Discriminant and Convergent Validity of the World Health Organization Six-Item Adult ADHD Self-Report Scale Screener Using the Stockholm Public Health Cohort

Abstract

Objective: The World Health Organization (WHO) Adult ADHD Self-Report Scale (ASRS) is intended to measure population prevalence of ADHD. The short version ASRS-6 has yet not been validated in a population setting. Our aim was to examine the validity of the ASRS-6 in a general population. Method: We used the Stockholm Public Health Cohort 2014. The convergent validity was assessed using item response theory (IRT). The discriminant validity was assessed by examining the correlation between the ASRS and known correlates. Results: The ASRS-6 was unidimensional albeit with hyperactivity and impulsivity items fitting less good. IRT analysis showed that the item difficulty ranged between easy to hard and that the four items on inattention had good or very good discriminatory ability. Correlates were all in the expected direction. Conclusion: The ASRS-6 has adequate validity in the general population but reflects the duality of ADHD having both inattention and hyperactivity/impulsivity as sufficient and non-necessary criteria.

Keywords

sensitivity and specificity screening attention-deficit hyperactivity impulsivity

Introduction

The World Health Organization (WHO) Adult ADHD Self-Report Scale (ASRS) was developed as part of the World Mental Health Initiative Surveys to obtain population-based estimates of the prevalence of ADHD in adults (Adler et al., 2006; Kessler et al., 2005). The scale was constructed from a combination of questions covering the 18 Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association, 1994) symptoms of inattention and hyperactivity or impulsivity, and 11 additional symptoms regarded as common clinical expressions of adult ADHD that were later not retained (Kessler et al., 2005). The discriminant validation of the scale items and a range of summary score indexes was tested against clinical interview data in a subsample nested within the development sample. While the agreement at the symptom level varied significantly, a simple summary index of the dichotomization of the 18 items was found to have overall good agreement with the clinicians’ diagnosis (area under the curve [AUC] = 0.84). A shorter version with only six items (ASRS-6) was also tested, which performed even better than the 18-item version (AUC = 0.96). A later study assessing the six-item version in health plan members found only moderate agreement with clinical diagnosis, but that agreement was better if the six items were summarized before dichotomization (AUC = 0.79 compared with 0.64; Kessler et al., 2007). As the primary aim of the ASRS development was to estimate prevalence, the optimal cutoff points was set to mirror the prevalence of diagnosis in the primary care sample (Kessler et al., 2007), emphasizing specificity over sensitivity. The ASRS-6 cutoff points at 4 or more of the 0 to 6 scale and 14 or more on the 0 to 24 scale rendered prevalence of 14% and 11%, to be compared with 8.5% in the original clinical sample. Much lower prevalence is reported in population-based samples where ADHD estimates range between 1.2% and 7.3% (de Zwaan et al., 2012; Fayyad et al., 2007; Kessler et al., 2006; Medina-Mora et al., 2005).

The U.S. primary care sample study also provided information on the internal consistency of the ASRS-6 scale (Kessler et al., 2007). All six items of the ASRS-6 belonged to a single underlying dimension, but with varying factor loadings and consequently also low Cronbach’s alpha, which the authors explained was because ADHD as a syndrome contained both inattention and/or hyperactivity (i.e., no necessary criteria). A two-factor latent structure differentiating the two hyperactivity/impulsivity items from the inattention items has also been presented in two subsequent studies (Hesse, 2013; Oerbeck et al., 2015). Common correlates of ADHD include not only mental comorbidity including mood and anxiety disorders (de Zwaan et al., 2012; Hesse, 2013; Kessler et al., 2006), other impulse control disorders (Hesse, 2013; Kessler et al., 2006), and substance use disorder/illicit use (Kessler et al., 2006), but presumably related correlates such as divorce (de Zwaan et al., 2012; Kessler et al., 2006) has been used to examine the concurrent validity of the ASRS.

The aim of this study was to examine the convergent and discriminant validity of the ASRS-6 in a general population sample. Because there is doubt whether older people have difficulty interpreting the ASRS questions (Kessler et al., 2005; Oerbeck et al., 2015), we examine the psychometric properties in separate age-groups.

Method

Population

This study was based on the 2014 wave of the Stockholm Public Health Cohort (SPHC-2014) which comprise three stratified random samples first recruited with postal questionnaires in 2002 (n = 21,182), 2006 (n = 34,704), and 2010 (n = 30,767; Svensson et al., 2013). The SPHC is collected by Statistics Sweden on behalf of Stockholm County Council every 4 years and encompass participants aged 18 to 84 (2002 and 2006) or 18 years and older (2010), and living in Stockholm county. Participants are drawn from the Swedish Total Population Register, randomly at the level of municipalities and smaller administrative areas in the Stockholm municipality. All previous 2010 wave participants were considered eligible (n = 74,416), also those who had moved from Stockholm County. The net sample after over-coverage by diseased and emigrants was reduced to 71,141 individuals. To these were sent an invitation letter with web login on November 11, 2014, followed by a Postal Questionnaire 2 weeks later, and up to four reminders (two including a postal questionnaire). The collection ended February 25, 2015, with 50,157 respondents (participation 70.5%). Statistics Sweden performed nonresponse analysis and constructed weights based on national register information on participants and nonparticipants (Lundstrom & Särndal, 1999).

ASRS-6

The six-item version of the ASRS used here comes from the ASRS-VI.I for use in persons 18 years and older and is a screening module in the WHO Composite International Diagnostic Interview schedule (Kessler et al., 2004. The Swedish version used is the official translated version obtained from the Harvard National Comorbidity Survey webpage. The translation was conducted by Alina Rodriguez, PhD, at the Department of Psychology, Uppsala University, Sweden, and is shown in Table 1. All ASRS items have five response categories: never, rarely, sometimes, often, and very often, scored 0 to 4. Summary indexes of the Likert-type score responses were computed for all those who replied to all six ASRS items (potential range 0 to 24). Following two studies by Kessler and colleagues (Kessler et al., 2005; Kessler et al., 2007), we also constructed four groups based on the score ranges: 0 to 9 (Strata 1), 10 to 13 (Strata 2), 14 to 17 (Strata 3), and 18 to 24 (Strata 4). To examine the recommended dichotomization of the items and their discriminatory ability, responding sometimes, often, and often to the first three items, and often, and very to the next three items was considered as prevalent symptoms. The ASRS has been shown to have good test–retest reliability (Kessler et al., 2007).

Table 1.

The Six-Item Adult ADHD Self-Report Scale Questions.

Domain	Question
Inattention	1. How often do you have trouble wrapping up the final details of a project, once the challenging parts have been done?
	2. How often do you have difficulty getting things in order when you have to do a task that requires organization?
	3. How often do you have problems remembering appointments or obligations?
	4. When you have a task that requires a lot of thought, how often do you avoid or delay getting started?
Hyperactivity/Impulsivity	5. How often do you fidget or squirm with your hands or feet when you have to sit down for a long time?
Hyperactivity/Impulsivity	6. How often do you feel overly active and compelled to do things, like you were driven by a motor?

Note. Response alternatives are never, rarely, sometimes, often, and very often.

Mental health and behavior correlates

The 10-item version of the Autism-Spectrum Quotient-10 (AQ-10) scale was used as a measure of autism (Allison, Auyeung, & Baron-Cohen, 2012). The AQ-10 consists of 10 descriptive statements of preferences and habits, each answered on a 4-point Likert-type scale: 1 = definitely agree, 2 = slightly agree, 3 = slightly disagree, 4 = definitely disagree. This version makes no reference to any time period, unlike the original which refer to the past 6 months. Four of the statements are positively phrased, and the Likert-type scores are reversed for these items. The scale covers five domains of autism: difficulties with social skills, routine, attention switching, imagination, and an attention to details. We constructed a summary index of the Likert-type responses (range = 10-40). Test–retest reliability for the original AQ version has been found to be satisfactory, r = .78 (Hoekstra, Bartels, Cath, & Boomsma, 2008). Psychological distress was measured using the 12-item version of the General Health Questionnaire (GHQ-12), which contains six positively and six negatively phrased questions about affective symptoms in the last few weeks. These are coded according to a Likert-type scale (e.g., for positively phrased items: 0 = better than usual, 1 = as usual, 2 = worse than usual, 3 = much worse than usual) which are summarized into a scale with range of 0 to 36. The GHQ-12 has shown good agreement with depression in the Stockholm population (Lundin, Hallgren, Theobald, Hellgren, & Torgén, 2016; Lundin, Åhs, et al., 2016). Substance use was measured using two questions on the frequency of intensive alcohol consumption and the use of Hash or Marijuana (Cannabis). Binge drinking was measured with a question on frequency of consuming one bottle of wine/five shots of hard liquor/four cans of beer (≥Alcohol By Volume [ABV] 4.5%) or six cans of beer (ABV = 2.25%-3.5%) at a single occasion, with response categories >5days/week, 3 to 4 days/week, 1 to 2 days/week, 2 to 3 days/month, 1 day/month, 1 to 6 days/year, and never. Last use of cannabis was recorded as last month, last year, >1 year ago, and never which was dichotomized as ever use. Binge drinking more than monthly was considered as frequent heavy episodic drinking. Smoking was based on questions on cigarette smoking with a probe question on frequency grouped into current high consumption, current moderate, smoke-quitter, and never-smoker, and was dichotomized as current smokers.

Correlates

Information on sex, age, country of birth, and marital status was obtained from the Population Register in January 2014, and information on income came from the Tax Register. Highest level of obtained education according to the Swedish version of the International Standard Classification of Education 1997 was obtained from the Register of Education and final school grades from upper secondary school (elective but usually attended) from the Register of Final Grades in upper secondary school at the National Agency for Education.

Information on school grades from finishing upper secondary school was available from 1973 Statistics Sweden. Income was log transformed after zero income was replaced with 1 Swedish Krona (about 0.12 US Dollar). The grade system was reformed in 1996, when the 5-point Likert-type participant grades were replaced with 4-point scores. Mean individual scores were computed for the older systems which were converted into percentile ranks separately for those graduating from 1973 through 1984 and 1985 through 1996.

Age was classified as young early adulthood (22-29 years), early adulthood (30-44 years), adulthood (45-64 years), and mature (65 years and older).

Statistical analysis

All analyses were conducted in SAS 9.4. Exploratory factor analysis with promax rotation was performed to examine the potential dimensionality of the Likert-type ASRS items. Eigenvalues, scree plots, and factor loadings were used to examine the number of potential dimensions. After confirming unidimensionality, we conducted a two-parameter logistic item response theory (IRT) model to assess item severity and item discrimination of the dichotomous items. Severity refers to the likelihood of endorsing the specific item at a given level of the latent continuum (the spectrum), and item discrimination refers to the ability of an item to discriminate respondents from lower to high levels of the latent continuum. The IRT analysis was based on dichotomous items. Analyses were conducted with PROC IRT. Our interpretation of the slope values follows the suggestions by Baker (1985): 0.01 to 0.34, very low discrimination; 0.35 to 0.64, low discrimination; 0.65 to 1.34, moderate discrimination; 1.35 to 1.69, high discrimination; and ≥1.70, very high discrimination. For comparisons with previous studies, we also computed Cronbach’s alpha coefficient for the ASRS index. Associations with correlates were examined in ordinary least squares (OLS) regression and logistic regression with ASRS scale score as independent variable. SAS SURVEYREG and SURVEYLOGISTIC procedures were used.

Results

Table 2 shows the descriptive statistics for the entire cohort and in the recommended groups of the ASRS scores (0-1, 2-3, 4-6 on the dichotomous scale, and 0-9, 10-13, 14-17, 18-24 on the Likert-type scale; Kessler et al., 2005). Because the cohort was originally sampled in 2002 and 2006, the age distribution is positively skewed. Moreover, men were less likely than women to participate. The overall prevalence for the Likert-type scale score range groups were as follows: 0 to 9 = 80.3%, 10 to 13 = 14.8%, 14 to 17 = 3.9%, and 18 to 24 = 1.0%. The prevalence for the dichotomized scale score range groups were as follows: 0 to 1 = 72.1%, 2 to 3 = 21.1%, and 4 to 6 = 6.8%.

Table 2.

Descriptive Statistics of the Cohort.

	All		ASRS
	n	%	Low 0-1	Medium 2-3	High 4-6
Total
Sex
Men	20,563	49.2	49.5	49.4	47.0
Women	27,179	50.8	50.5	50.6	53.0
Age
Young early adulthood	1,462	15.7	13.0	20.7	30.1
Early adulthood	8,638	15.7	28.8	34.6	34.5
Adulthood	18,700	31.5	33.3	27.5	24.4
Mature	18,942	22.5	24.9	17.2	11.0
Country of birth
Sweden	40,621	73.7	74.0	73.3	71.6
Other European country	4,608	12.6	12.9	11.9	10.8
Asia	1,224	8.2	7.8	8.4	11.7
Rest of the world	880	5.5	5.3	6.3	6.0
Household income
1st quartile	19,070	44.6	42.8	47.7	54.4
2st quartile	11,213	22.4	22.5	22.1	22.5
3rd quartile	7,525	15.1	15.8	13.9	11.2
4th quartile	9,523	17.8	18.8	16.3	11.9
Marital status
Married	3,300	4.5	4.7	3.8	3.4
Unmarried	10,704	35.8	32.4	42.6	52.9
Divorce	26,481	47.3	50.4	41.5	32.4
Widow(er)	7,213	12.4	12.5	12.1	11.3
Education
9 or less years	5,801	16.5	16.9	14.6	16.0
Upper secondary	18,229	38.2	38.4	37.2	39.3
Higher education	23,534	45.3	44.8	48.2	44.6
Grades (for those graduating 1973-1996)
1st quartile	3,847	27.6	27.2	27.6	34.3
2st quartile	3,515	24.7	25.0	24.1	22.4
3rd quartile	3,683	24.1	23.5	26.2	24.6
4th quartile	3,762	23.6	24.4	22.0	18.7

Note. ASRS = ADHD Self-Report Scale.

Factor analysis of the Likert-type ASRS items indicated that they comprise a single factor: The first three eigenvalues were 2.13, 0.36, and –.034. Based on the Kaiser Guttman criteria, this implies a dominant global factor, but there are positive eigenvalues, and theoretically, there is a lower order structure. The scree test indicated one sharp drop. A two-factor solution increased the finale community estimate from 2.20 to 2.84 (higher is better). The two-factor solution separated the two Hyperactivity/Impulsivity items that had the lowest loading into the single factor solution (Table 3). Eigenvalues of the reduced correlation matrix increased from 37% to 47% with a two-factor solution. There is, however, a strong correlation between the two factors (inter-factor correlation = .45).

Table 3.

ASRS Rotated Factors Loading.

Subscale	Item no.	Single factor	Two factors
Subscale	Item no.	Factor 1	Factor 1	Factor 2
Inattention	1	0.73	0.75	0.001
	2	0.76	0.85	−0.06
	3	0.51	0.43	0.12
	4	0.70	0.65	0.09
Hyperactivity/Impulsivity	5	0.47	0.06	0.73
Hyperactivity/Impulsivity	6	0.35	0.01	0.55

Note. Single factor solution shows un-rotated factor pattern and two-factor solution shows rotated pattern. ASRS = ADHD Self-Report Scale. Bold values signify primary loadings.

Table 4 shows the IRT discrimination and severity parameters for the six ASRS items when dichotomized according to the manual. The severity ranged from 0.9 to 2.9 in the entire cohort. Moderate discriminatory was found for the two Hyperactivity/Impulsivity items and one of the Inattention symptoms. Age-stratified analyses showed low discriminatory ability for the Inattention items in all age-groups.

Table 4.

Difficulty and Discrimination of Bimodal ASRS Items.

ASRS item no.	All		Young		Medium		Old middle age		Retired
ASRS item no.	Difficulty	Slope	Difficulty	Slope	Difficulty	Slope	Difficulty	Slope	Difficulty	Slope
1	0.70	2.56	0.50	1.90	0.46	1.99	0.69	2.55	1.08	1.91
2	0.96	2.93	0.79	2.77	0.94	2.72	0.97	3.25	0.86	10.48
3	1.99	1.36	1.67	1.25	1.77	1.18	2.06	1.37	2.26	1.35
4	1.76	2.32	0.95	2.19	1.45	2.20	1.78	2.45	2.24	2.06
5	2.28	1.02	0.74	0.86	1.74	0.89	2.40	0.96	3.75	0.83
6	3.75	0.89	2.62	0.81	3.52	0.78	3.87	0.82	6.43	0.63

Note. ASRS = ADHD Self-Report Scale.

Table 5 shows the association between the ASRS index score (sum of Likert-type responses) and concomitant measures of autism, psychological distress, school grades (OLS coefficients), and smoking cannabis use and heavy episodic alcohol drinking (odds ratios). ASRS scores increase the prevalence of autism, psychological distress, smoking, cannabis use, and heavy episodic alcohol drinking. School grades and income were negatively associated with ASRS scores. There were no large variations in estimates across age-groups.

Table 5.

Association Between the ASRS Scale Score and the Correlates.

Correlates	Men				Women
Correlates	Beta	SE	p		Beta	SE	p
Psychological distress
Young early adulthood	0.67	0.08	<.0001		0.52	0.06	<.0001
Early adulthood	0.56	0.03	<.0001		0.60	0.03	<.0001
Adulthood	0.65	0.03	<.0001		0.70	0.02	<.0001
Mature	0.57	0.03	<.0001		0.68	0.03	<.0001
AQ-10
Young early adulthood	0.35	0.05	<.0001		0.39	0.04	<.0001
Early adulthood	0.36	0.02	<.0001		0.36	0.02	<.0001
Adulthood	0.33	0.02	<.0001		0.38	0.02	<.0001
Mature	0.36	0.02	<.0001		0.37	0.02	<.0001
log income (log t SEK)
Young early adulthood	−0.02	0.02	0.3716	−0.03	0.02	0.0759
Early adulthood	−0.03	0.005	<.0001	−0.01	0.01	0.0080
Adulthood	−0.03	0.006	<.0001	−0.02	0.005	0.0002
Mature	−0.04	0.0163	0.0168	−0.01	0.004	0.0055
Upper secondary school grades (quartiles)
Young early adulthood	−0.006	0.009	0.4916	−0.0269	0.007	<.0001
Early adulthood	−0.004	0.006	0.4980	−0.0124	0.005	0.0217
	OR	95% CI		OR	95% CI
Frequent heavy episodic drinking
Young early adulthood	0.99	[0.94, 1.04]		1.06	[1.02, 1.11]
Early adulthood	1.04	[1.01, 1.07]		1.05	[1.02, 1.08]
Adulthood	1.02	[1.00, 1.04]		1.02	[1.00, 1.04]
Mature	1.03	[1.00, 1.07]		1.01	[0.98, 1.05]
Cannabis use
Young early adulthood	1.08	[1.02, 1.14]		1.11	[1.07, 1.16]
Early adulthood	1.08	[1.06, 1.11]		1.07	[1.05, 1.09]
Adulthood	1.07	[1.05, 1.09]		1.08	[1.06, 1.11]
Mature	1.06	[1.00, 1.12]		1.10	[1.02, 1.18]
Current smoker
Young early adulthood	1.11	[0.99, 1.25]		1.08	[1.01, 1.15]
Early adulthood	1.02	[0.96, 1.10]		1.08	[1.04, 1.12]
Adulthood	1.02	[0.99, 1.06]		1.05	[1.02, 1.07]
Mature	0.99	[0.96, 1.03]		0.98	[0.95, 1.01]

Note. ASRS = ADHD Self-Report Scale; AQ-10 = Autism-Spectrum Quotient-10; OR = odds ratio; CI = confidence interval.

Discussion

Concluding the Findings

We found that the ASRS is well described as a unidimensional factor, potentially with a higher order factor separating the two hyperactivity/impulsivity items from the four items covering inattention. Applying IRT on the symptoms when dichotomized according to the standard mode of scoring confirmed a better discrimination of the (last) items when dichotomized more conservatively. Overall prevalence of 14 or more on the 0 to 24 scale (screen positive) and 4 or more on the 0 to 6 scale were 4.9% and 6.8%, respectively. The ASRS was found to correlate in the expected direction with measures of autism, psychological distress, and cannabis use in all age-groups and both sex. Associations with smoking, heavy episodic alcohol drinking, income, and school grades were also found, but less consistently across age and sex.

Comparison With Previous Studies and Explaining the Findings

Exploratory analysis did not obviously reveal a second factor, which is in line with the original scale construction, but in contrast to two previous studies on the ASRS-6 where the Hyperactivity/Impulsivity items were found to be separate from the Inattention items (Hesse, 2013; Oerbeck et al., 2015). Both Hesse et al. and Oerbeck et al. argue for a two-factor solution (Hesse, 2013; Oerbeck et al., 2015), although in the former study, the second eigenvalue was only 0.24 which similar to our study may be interpreted as a lower order factor. In our study as well as the studies by Hesse et al. and Oerbeck et al., it is the two items on inattention that correlates poorly with the overall construct. This was commented already by the original constructors of the ASRS-6, reflecting that ADHD is a syndrome comprising of two types of behavioral problems, inattention and/or hyperactivity-impulsivity (Kessler et al., 2007). It should be noted that lower order factors exist in the 18-item version of ASRS, but that these would be hard to retain using only six items.

The dichotomization of the Likert-type answers was originally guided by item-level agreement with clinically judged symptom prevalence (high sensitivity and specificity), which resulted in that some items were considered present if answer with “sometimes” or higher (first three items in ASRS-6), and others with “often” or “very often.” However, our IRT analyses show that the difficulty of the items spans from easy (below 1) to hard (above 1), as intended if you want to create an index to measure a continuous normally distributed phenomenon. Items 1, 2, and 4 were found to have very high and Item 3 high discriminatory ability, whereas Items 5 and 6 (the hyperactivity/inattention items) discriminated only moderately.

We found that the ASRS correlated significantly with autism and psychological distress, which is in concert with previous studies from Sweden (Capusan, Bendtsen, Marteinsdottir, & Larsson, 2016), Germany (de Zwaan et al., 2012), and the United States (Kessler et al., 2006). The strongest association was between ADHD and ASD, as expected from previous population-based samples in Sweden, and in agreement with clinical observational studies. In twins, however, co-occurrence of ASD and ADHD item correlations for interests and inattention, repetitive and restricted behavior, and hyperactivity/impulsivity was generally low to moderate (T. J. Polderman, Hoekstra, Posthuma, & Larsson, 2014), and AQ-short items correlated only moderately to not at all with Conners’ Adult ADHD Rating Scale items (T. J. C. Polderman et al., 2013). The association between the ASRS and psychiatric distress is in line with general population studies from the United States where mood and anxiety disorders were significantly more often reported among respondents with ADHD (Kessler et al., 2006), and a strong correlation was reported between ASRS and Kessler depression scale in a student sample, r = .47 (Hesse, 2013).

Less strong associations, but significant and in the expected direction, were found between the ASRS and smoking, cannabis use, and hazardous alcohol consumption. This in part contrasts previous studies from Sweden where twins with ADHD were more often alcohol dependent, alcohol abuser, and current cannabis users. Similarly in our study, nicotine use was associated with ADHD not only in women (Capusan et al., 2016). Kessler found increased prevalence of drug dependence but not alcohol use disorders among those with ADHD compared with non-ADHD population controls (Kessler et al., 2006). Substance use has been suggested as a self-regulation mechanism for restlessness and mood regulation (Capusan et al., 2016). Income and school grades had no or very small associations with the ASRS score, which is in contrast with previous studies where inattentiveness in ADHD has been found to negatively affect academic achievement (Frazier, Youngstrom, Glutting, & Watkins, 2007) in both college students and adult samples. Adult ADHD in the national Comorbidity Survey was, however, not related to income or education (Kessler et al., 2006).

Implication of the Findings

The tests of the validity of the ASRS conducted here indicate that this short scale is well suited as a statistical measure for use in public health surveys. Using the proposed cut points, the prevalence range from 4.9% and 6.8%, which agree with the original report of 4% and later 1% to 7% reported in public mental health surveys (de Zwaan et al., 2012; Fayyad et al., 2007; Kessler et al., 2006; Medina-Mora et al., 2005). The recommended cutoff points (Kessler et al., 2007) were chosen to reflect prevalence in a clinical sample, despite the low sensitivity for these cutoff points (sensitivity and specificity was 39.1 and 88.3 for the 0 to 6 scoring, and 64.9 and 94.0 for the 0 to 24 scoring). Depending on the purpose, this cut point may not be optimal, because it will produce a larger share of false negatives (e.g., not favorable for a clinical screener). For use in statistics and research, this high specificity would help minimize dilution of the true cases with false positive (if needing to dichotomize the scale). The ASRS was previously decided to not work well for older individuals (though not reported), which is confirmed in our study (Kessler et al., 2005).

Methodological Consideration

The ASRS-6 contains too few items to construct separate indices for hyperactivity and impulsivity.

We had no clinical interview data on ADHD and thus could not assess the agreement between ASRS scale and ASD. In a small clinical sample of Swedish Twins, the ASRS correlated with all the 18 DSM symptoms of ADHD as conceptualized in the ADHD-STAGE instrument (correlation of .63; p < .0001; Larsson et al., 2013), but here, ASRS was used as the reference index. Moreover, as the sensitivity and the specificity are not known, it is not known to what extent the estimated prevalence reflect the true population prevalence.

Conclusion

The ASRS-6 has adequate validity in the general population. It is largely unidimensional although hyperactivity/impulsivity items possibly tap into a separate latent construct than inattention. This most likely reflects the duality of ADHD (Attention-Deficit and/or Hyperactivity Disorder) where both hyperactivity/impulsivity and inattention are sufficient but not necessary criteria.

Footnotes

Authors Note

The Stockholm Public Health Cohort is available for researchers. For data requisition, see

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study is supported by FundRef Funding Sources Forskningsrådet om Hälsa, Arbetsliv och Välfärd (Grant/Award Number: “2014–1743”).

Author Biographies

Andreas Lundin, PhD, is a research coordinator at the Department of Public Health Sciences, Karolinska Institutet. His research covers mental health and substance use.

Kyriaki Kosidou, MD, PhD in medical sciences from Karolinska Institutet, Sweden, is a psychiatrist and researcher at the Centre for Epidemiology & Community Medicine, specializing in psychiatric epidemiology. She is also a researcher at the Department of Public Health Sciences, Karolinska Institutet.

Christina Dalman, MD, PhD, is a professor of psychiatry at the Department of Public Health Sciences, Karolinska Institutet, and head of the unit of Mental Health at Centre for Epidemiology & Community Medicine. Her research interests cover vulnerability and risk factors for psychiatric disorders with special regard to serious and long-standing conditions such as psychotic disorders.

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