Graphical Models for Inference Under Outcome-Dependent Sampling

We consider situations where data have been collected such that the sampling depends on the outcome of interest and possibly further covariates, as for instance in case-control studies. Graphical models represent assumptions about the conditional independencies among the variables. By including a node for the sampling indicator, assumptions about sampling processes can be made explicit. We demonstrate how to read off such graphs whether consistent estimation of the association between exposure and outcome is possible. Moreover, we give sufficient graphical conditions for testing and estimating the causal effect of exposure on outcome. The practical use is illustrated with a number of examples.Comment: Published in at http://dx.doi.org/10.1214/10-STS340 the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org

Undersøgelse af De Nationale Tests måleegenskaber

Denne rapport indeholder en omhyggelig analyse af de måletekniske egenskaber af de nationale test i læsning i 8. klasse i 2017. Analyserne bygger på svarene på alle opgaver fra alle 48.481 elever i 8. klasse i 2017. Analysen er foretaget ved hjælp af den samme Rasch-model som blev anvendt i forbindelse med udviklingen og afprøvningen af de nationale test. Eventuelle forskelle på det som analysen af datamaterialet fra 2017 måtte afsløre, i forhold til det som de nationale test producerer, kan derfor ikke skyldes at denne analyse bruger andre metoder og stiller andre krav til test, end dem der blev brugt i forbindelse med udviklingen af de nationale test.Resultaterne af analysen kan ganske kort opsummeres på følgende måde:1)    Nationale test anvender opgavernes sværhedsgrader til at udvælge opgaver til elever og til at beregne mål for hvor dygtige eleverne er. Disse sværhedsgrader er forkerte, og der var i 2017 mange tilfælde af meget store forskelle på de sværhedsgrader som nationale test benytter, og de sande sværhedsgrader.2)    Konsekvensen af at nationale tests sværhedsgrader er forkerte, er at beregningerne af dygtigheden er forkert og kan være direkte vildledende. Analyserne i kapitel 4 giver flere eksempler på at det rent faktisk er tilfældet, både når man ser på testresultater for enkelte elever, og når man ser på fordelingen af læsefærdigheden i 2017. Nationale tests resultater tegner med andre ord et forvrænget billede af situationen.3)    Anvendelsen af forkerte sværhedsgrader betyder at den adaptive algoritme vælger opgaver på en uhensigtsmæssig måde som – selvom målingerne af dygtigheden ikke havde været systematisk forkerte, og selvom analyserne også viser at den adaptive algoritme fungerer som den skal – ville forringe sikkerheden på målingerne. Resultaterne i kapitel 4 og 5 giver flere eksempler på at dette ikke blot er noget der kan påvises at følge logisk af problemerne med sværhedsgraderne, men at det også kan ses i data fra 2017.4)    Undersøgelsen i kapitel 4 af opgavernes tilpasning til eleverne viser at der i to af de tre områder som eleverne testes i (profilområder), kun er et meget begrænset udvalg af opgaver til dygtige og meget dygtige elever. Det kan betyde at disse elever vil opleve at få de samme opgaver i den obligatoriske test som de allerede har fået i den frivillige test, og det betyder at de skal besvare flere opgaver end nødvendigt for at opnå tilstrækkelig sikkerhed på resultatet.5)    Med hensyn til usikkerheden viser analyserne også at ministeriets beslutning om at slække på kravene til målingernes sikkerhed fører til testresultater der er så usikre at de er uanvendelige på elevniveau. Dette problem ville også være der selvom der ikke var problemer med opgavernes sværhedsgrader, men fejlene i sværhedsgraderne forstærker problemet med usikkerheden.6)    En undersøgelse af datas tilpasning til Rasch-modellen i kapitel 4 viser at der ikke er belæg i data for at sige at de tre profilområder i læsning måler én og samme færdighed, men analysen tyder på at det kan give mening at se afkodning og tekstforståelse som én dimension. En sådan sammenlægning af profilområder ville kunne forøge sikkerheden på elevernes resultater.7)    Analyserne i kapitel 5 viser at der er situationer hvor elevens færdigheder i læsning ikke kommer til udtryk i dele af testforløbet, og at beregningerne derfor systematisk undervurderer hvor godt eleven læser. De nævnte situationer, hvor dele af testforløbet er mislykkedes, er hyppigst i starten af forløbet, men forekommer også undervejs. Denne analyse kan ikke sige noget konkret om hvor ofte der er problemer med dele af testforløbene, men vi kan konstatere at det var særdeles let at finde sådanne eksempler ved blot at kigge datamaterialet igennem. Af den årsag forventer vi at hyppigheden af delvist mislykkede testforløb hvor elevernes færdigheder undervurderes, er med til at tegne et mere pessimistisk billede af danske elevers læsefærdigheder, end der er belæg for

Consequences of Screening in Lung Cancer: Development and Dimensionality of a Questionnaire

AbstractObjectiveThe objective of this study was to extend the Consequences of Screening (COS) Questionnaire for use in a lung cancer screening by testing for comprehension, content coverage, dimensionality, and reliability.MethodsIn interviews, the suitability, content coverage, and relevance of the COS were tested on participants in a lung cancer screening program. The results were thematically analyzed to identify the key consequences of abnormal and false-positive screening results. Item Response Theory and Classical Test Theory were used to analyze data. Dimensionality, objectivity, and reliability were established by item analysis, examining the fit between item responses and Rasch models.ResultsEight themes specifically relevant for participants in lung cancer screening results were identified: “self-blame,” “focus on symptoms,” “stigmatization,” “introvert,” “harm of smoking,” “impulsivity,” “empathy,” and “regretful of still smoking.” Altogether, 26 new items for part I and 16 new items for part II were generated.These themes were confirmed to fit a partial-credit Rasch model measuring different constructs including several of the new items.ConclusionIn conclusion, the reliability and the dimensionality of a condition-specific measure with high content validity for persons having abnormal or false-positive lung cancer screening results have been demonstrated. This new questionnaire called Consequences of Screening in Lung Cancer (COS-LC) covers in two parts the psychosocial experience in lung cancer screening. Part I: “anxiety,” “behavior,” “dejection,” “sleep,” “self-blame,” “focus on airway symptoms,” “stigmatization,” “introvert,” and “harm of smoking.” Part II: “calm/relax,” “social network,” “existential values,” “impulsivity,” “empathy,” and “regretful of still smoking.

Validation of the Early Functional Abilities scale:An assessment of four dimensions in early recovery after traumatic brain injury

Objective: The Early Functional Abilities scale assesses the restoration of brain function after brain injury, based on 4 dimensions. The primary objective of this study was to evaluate the validity, objectivity, reliability and measurement precision of the Early Functional Abilities scale by Rasch model item analysis. A secondary objective was to examine the relationship between the Early Functional Abilities scale and the Functional Independence Measurement™, in order to establish the criterion validity of the Early Functional Abilities scale and to compare the sensitivity of measurements using the 2 instruments. Methods: The Rasch analysis was based on the assessment of 408 adult patients at admission to sub-acute rehabilitation in Copenhagen, Denmark after traumatic brain injury. Results: The Early Functional Abilities scale provides valid and objective measurement of vegetative (autonomic), facio-oral, sensorimotor and communicative/cognitive functions. Removal of one item from the sensorimotor scale confirmed unidimensionality for each of the 4 subscales, but not for the entire scale. The Early Functional Abilities subscales are sensitive to differences between patients in ranges in which the Functional Independence Measurement™ has a floor effect. Conclusion: The Early Functional Abilities scale assesses the early recovery of important aspects of brain function after traumatic brain injury, but is not unidimensional. We recommend removal of the “standing” item and calculation of summary subscales for the separate dimensions

Socioeconomic status and duration and pattern of sickness absence. A 1-year follow-up study of 2331 hospital employees

BACKGROUND: Sickness absence increases with lower socioeconomic status. However, it is not well known how this relation depends on specific aspects of sickness absence or the degree to which socioeconomic differences in sickness absence may be explained by other factors. The purpose of the study was to examine differences in sickness absence among occupational groups in a large general hospital; how they depend on combinations of frequency and duration of sickness absence spells; and if they could be explained by self-reported general health, personal factors and work factors. METHODS: The design is a 1-year prospective cohort study of 2331 hospital employees. Baseline information include job title, work unit, perceived general health, work factors and personal factors recorded from hospital administrative files or by questionnaire (response rate 84%). Sickness absence during follow-up was divided into short (1-3 days), medium (4-14 days) and long (>14 days) spells, and into no absence, "normal" absence (1-3 absences of certain durations) and "abnormal" absence (any other absence than "normal"). Socioeconomic status was assessed by job titles grouped in six occupational groups by level of education (from doctors to cleaners/porters). Effects of occupational group on sickness absence were adjusted for significant effects of age, gender, general health, personal factors and work factors. We used Poisson or logistic regression analysis to estimate the effects of model covariates (rate ratios (RR) or odds ratios (OR)) and their 95% confidence intervals (CI). RESULTS: With a few exceptions sickness absence increased with decreasing socioeconomic status. However, the social gradient was quite different for different types of sickness absence. The gradient was strong for medium spells and "abnormal" absence, and weak for all spells, short spells, long spells and "normal" absence. For cleaners compared to doctors the adjusted risk estimates increased 4.2 (95% CI 2.8-6.2) and 7.4 (95% CI 3.3-16) times for medium spells and "abnormal" absence, respectively, while the similar changes varied from 0.79 to 2.8 for the other absence outcomes. General health explained some of the social gradient. Work factors and personal factors did not. CONCLUSIONS: The social gradient in sickness absence was different for absences of different duration and patterns. It was strongest for absences of medium length and "abnormal" absence. The social gradient was not explained by other factors

School-related mediators in social inequalities in smoking: a comparative cross-sectional study of 20,399 adolescents

<p>Abstract</p> <p>Background</p> <p>The aim of this study was to examine the associations between social inequalities and daily smoking among 13 and 15 year olds, and to determine the role of students' academic achievement and school satisfaction in these associations.</p> <p>Methods</p> <p>HBSC is an international study including adolescents from 32 countries in Europe, Israel, and North America. The present study was based on information from 20,399 adolescents from Denmark, Sweden, Norway, Finland and the United Kingdom. Data were analysed by regression models.</p> <p>Results</p> <p>The initial analyses showed significant inequality in daily smoking in all countries except for Sweden. When adjusted for the mediating role of academic achievement, estimates were attenuated, but remained significant in three countries.</p> <p>Conclusion</p> <p>The study found social inequality in daily smoking in Denmark, Sweden, Norway, Finland and United Kingdom, as well as inequalities in students' academic achievement and school satisfaction. The analyses also showed that above average academic achievement was associated with lower OR of smoking. Teachers and politicians may find this information useful, and allocate resources to give higher priority to a supportive environment in schools especially for children and adolescents in lower social groups. Subsequently this prioritisation might contribute to reducing smoking in this group.</p

Item analysis using Rasch models confirms that the Danish versions of the DISABKIDS (R) chronic-generic and diabetes-specific modules are valid and reliable

BACKGROUND: Type 1 Diabetes (T1D) has a negative impact on psychological and overall well-being. Screening for Health-related Quality of Life (HrQoL) and addressing HrQoL issues in the clinic leads to improved well-being and metabolic outcomes. The aim of this study was to translate the generic and diabetes-specific validated multinational DISABKIDS® questionnaires into Danish, and then determine their validity and reliability. METHODS: The questionnaires were translated using a validated translation procedure and completed by 99 children and adolescents from our diabetes-department; all diagnosed with T1D and were aged between 8 and 18 years old. The Rasch and the graphical log linear Rasch model (GLLRM) were used to determine validity. Monte Carlo methods and Cronbach’s α were used to confirm reliability. RESULTS: The data did not fit a pure Rasch model but did fit a GLLRM when item six in the independence scale is excluded. The six subscales measure different aspects of HrQoL indicating that all the subscales are necessary. The questionnaire shows local dependency between items and differential item functioning (DIF). Therefore age, gender, and glycated hemoglobin (HbA1c) levels must be taken into account when comparing HrQoL between groups. CONCLUSIONS: The Danish versions of the DISABKIDS® chronic-generic and diabetes-specific modules provide valid and objective measurements with adequate reliability. These Danish versions are useful tools for evaluating HrQoL in Danish patients with T1D. However, guidelines on how to manage DIF and local independence will be required, and item six should be rephrased. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12955-017-0618-8) contains supplementary material, which is available to authorized users

Measurement of alienation among adolescents:construct validity of three scales on powerlessness, meaninglessness and social isolation

Abstract Background Psychological alienation is an important concept in the study of adolescents’ health and behavior but no gold standard for measuring alienation among adolescents exists. There is a need for new scales with high validity for use in adolescent health and social research. The purpose of the present study was to develop and validate alienation scales in accordance with Seeman’s conceptualization of alienation focusing on three independent variants specifically relevant in adolescent health research: powerlessness, meaninglessness and social isolation. Methods Cross-sectional data from 3083 adolescents aged 13 to 15 years from the Danish contribution to the cross-national study Health Behaviour in School-aged Children (HBSC) were used. We identified and developed items, addressed content and face validity through interviews, and examined the criterion-related construct validity of the scales using graphical loglinear Rasch models (GLLRM). Results The three scales each comprised three to five face valid items. The powerlessness scale reflected the adolescent’s expectancy as to whether his/her behavior can determine the outcome or reinforcement he/she seeks. The meaninglessness scale reflected the expectancy as to whether satisfactory predictions regarding the effects of one’s behavior are possible. Finally, the social isolation scale reflected whether the adolescent had a low expectancy for inclusion and social acceptance. All scales contained some uniform local dependency and differential item functioning. However, only to a limited degree, which could be accounted for using GLLRM. Thus the scales fitted GLLRMs and can therefore be considered to be essentially construct valid and essentially objective. Conclusion The three alienation scales appear to be content and face valid and fulfill the psychometric properties of a good construct valid reflective scale. This suggests that the scales may be appropriate in future large-scale surveys to examine the relation between alienation and a range of adolescent health outcomes such as health, behavior and wellbeing