PEDIATRICS Vol. 105 No. 3 March 2000, pp. 569-574

Parental Perspectives of the Health Status and Health-Related Quality of Life of Teen-Aged Children Who Were Extremely Low Birth Weight and Term Controls

Saroj Saigal, MD^{*, §}, Peter L. Rosenbaum, MD^{*, §}, David Feeny, PhD, Elizabeth Burrows, MBA^{*, §}, William Furlong, MSc, Barbara L. Stoskopf, RN, MHSc^{*, §}, and Lorraine Hoult, BA^{*, §}

From the Departments of ^* Pediatrics and  Clinical Epidemiology and Biostatistics, and the Centre for Health Economics and Policy Analysis, McMaster University, ^§ Children's Hospital at Hamilton Health Sciences Corporation, Hamilton, Ontario, Canada.

	ABSTRACT

Top Abstract Methods Results Discussion References

Objectives.  To compare the health status and health-related quality of life of teen-aged children who were extremely low birth weight (ELBW) with matched controls from the perspective of their parents.

Study Design.  Geographically defined cohort; longitudinal follow-up; cross-sectional interviews. Participants: parents of 149/169 (88%) ELBW children between 12 and 16 years of age (including 41 children with neurosensory impairments) and 126/145 (87%) parents of term controls. Health status of the teenagers was classified according to the 6 attributes of the Health Utilities Index Mark 2, based on information obtained during parent interviews. Parents were asked to imagine themselves living in their own child's health state and 4 preselected hypothetical health states when providing directly measured standard gamble utility scores.

Results.  Parents of ELBW children reported a higher frequency and more complex functional limitations than parents of controls for their own children's health status. Also, the mean utilities were lower (ELBW = .91 vs controls = .97) and the variability in their scores was greater. There were no differences in the valuation of the hypothetical health states provided by parents of ELBW and control children.

Conclusions.  ELBW children were reported to have a greater burden of disability than were control children based on parental descriptions. Nonetheless, parents of ELBW children, on average, rated the health-related quality of life of their children fairly high. Thus, differences in reported functional status are not necessarily associated with lower utility scores.  Key words:  health status, quality of life, adolescence, extremely low birth weight, parental.

With recent advances in perinatal care, the survival of very premature infants has gradually improved without a concomitant increase in the prevalence of impairments.^1,2 However, reports to school age show that in extremely low birth weight (ELBW) infants social, behavioral, and educational problems constitute an increasingly large proportion of the overall morbidity.^3-6 Historically, the indicators and measures used to evaluate health outcomes have been chosen from the viewpoint of health care providers. Although reliance on parental report is a basic part of the traditional medical practice of pediatricians, there is considerable skepticism as to the ability of parents to provide valid data about the development of their child.^7,8 To date, parents have been underutilized in the identification of developmental and behavioral problems in children.^7-10 Moreover, parents may have a very different perspective than do health professionals regarding the problems they perceive to be most important for their child and family, as well as in the valuation of the same.¹¹ Recent studies have shown that the dimensions of health and the values of individuals whose health status is being measured may differ from those of health care providers, proxy respondents, and members of society.^11-13 Therefore, there is increasing support for the measurement of outcomes from the perspective of patients or their families in all areas of medicine.¹⁴

We previously reported on the health status and health-related quality of life (HRQL) of a cohort of children who were ELBW using the Health Utilities Index.^15,16 Two different perspectives were obtained. In the first study, at 8 years of age,^17,18 health status was retrospectively classified based on assessments provided by health professionals, and utility scores for each subject were estimated indirectly using a formula derived from measurements obtained from general-population parents.¹⁹ More recently, we used direct preference measurement techniques to describe the outcome from the perspective of the children at adolescence.²⁰ The objectives of the present study are to describe and to compare the health status and HRQL of the same cohort of children in adolescence, this time from the perspective of their parents.

	METHODS

Top Abstract Methods Results Discussion References

Study Subjects and Assessors

The subjects of this study were a cohort of ELBW survivors (1000 g birth weight) born between 1977 to 1982 to residents of a geographically defined region in central-west Ontario.³ There were 179 ELBW survivors who were followed longitudinally from birth. Ten children subsequently died, leaving 169 survivors.

The control subjects (n = 145) were born at term and weighed >2500 g at birth. They were recruited at 8 years of age from a random list of children provided by the board of education of the City of Hamilton and the Hamilton-Wentworth Roman Catholic Separate School Board and were matched with the ELBW cohort for age, sex, and social class.³ One parent of each ELBW and control subject was invited to be interviewed about the health status and HRQL of their child when the children were between 12 and 16 years of age.

Measurement of Health Status and HRQL

A custom interview script was used to collect information from each parent to classify the health status of the teenage subject according to the Health Utilities Index Mark 2 (HUI2) multiattribute health status classification system.^15,16 The following 6 attributes were assessed: sensation (vision, hearing, and speech), mobility, emotion, cognition, self-care, and pain. Each attribute has between 4 and 5 defined functional levels of severity, ranging from normal function to severe functional limitations. In addition, parental perception of the overall current health status of the teens (excellent, good, fair, or poor health) was obtained in response to a single question.

After the assessment of the health status, we directly measured preferences for the subjectively-defined current health state of the teen subjects. Two preference measurement techniques²¹ were used to elicit preference-based HRQL scores from the parents for the health state of teenagers and for 4 preselected hypothetical health states. The visual analog scaling technique (feeling thermometer) measures preferences under conditions of certainty and provides value scores ranging from 0 (least desirable health state) to 100 (most desirable health state). The standard gamble (chance board) measures preferences under conditions of risk (uncertainty) and involves a lottery approach to measurement. Preference scores on the standard gamble were transformed, if necessary, onto a scale in which dead = 0.0 and perfect health = 1.0, to ensure comparability when aggregating results across individuals. Briefly, in cases in which the rater considered the health state to be worse than dead, the negative utility for the state was determined directly from the standard gamble.²² The negative utilities were then rescaled onto a 1.0 to .0 interval using the nonlinear transformation: y = x/(1  x), described by Patrick et al.²³

The 4 hypothetical health states were selected as reference states from those reported for ELBW survivors at 8 years of age.^17,18 Each hypothetical health state was given a unisex name (Jamie, Chris, Pat, and Sandy).²⁰ These health states were used to provide a context within which respondents could rate the health state of their own child and ranged from a mild, single-attribute problem (Jamie), to moderate dysfunction (Chris), to severe, multiple problems (Pat and Sandy). The parents were asked to imagine themselves living in each of the above states of health, as well as in the health state of their own child, for the next 60 years. The instruments were pilot tested on a group of nonstudy parents.

Interview Protocol

Parents were interviewed in a private room at the McMaster University Health Sciences Center by trained nonclinical, professional interviewers who were blind to the group status. At the start of the interview, the parents were introduced to the HUI2 attributes and functional levels and were asked to respond to questions to classify their child's health status using 1 level from each of the 6 attributes. The parents were then asked to rate the 4 hypothetical health state descriptions on the feeling thermometer, followed by the health state of their own child. Although the feeling thermometer was used before the standard gamble to familiarize the respondents with the concept of preferences, these data will not be presented because the reliability and validity of the visual analog scale instrument are not as high.²⁴ Lastly, the parents were asked to participate in the measurement of the same health states using the chance board.²¹ The concept of probability was explained to the parents using an illustrative probability wheel and parents were given 2 practice sessions to test their comprehension of the task before being asked standard gamble questions about utilities of the above health states.

At the end of each interview, the interviewers reported their impression of each respondent's comprehension and concentration on the tasks assigned using a 5-point Likert scale. As well, the respondents were asked whether they encountered any difficulties and whether the questions asked allowed them to report how they actually felt. These data were subsequently analyzed to assess the quality of the interviews. For descriptions of the health states and for additional details of preference measurement techniques, please refer to our previous publication.²⁰

Ethics Approval

The study was approved by the institutional review board of the Hamilton Health Sciences Corporation. Written informed consent was obtained from the parents of all children.

Statistical Analyses

Tests Pearson ² test with the Yates correction for continuity was used to test for differences between ELBW and control parent respondents in reporting the number of attributes affected and for frequencies of attribute levels used to describe their child's health status. Student's t tests for unpaired data were used to test equality of mean utility scores between parents of ELBW and control teenagers; 95% confidence intervals were calculated for differences in mean scores between ELBW and control groups. The variance ratio test was used to test for homogeneity of variance between mean utility scores reported by ELBW and control parent groups.

	RESULTS

Top Abstract Methods Results Discussion References

Parental and teen demographic information on 149/169 (88%) ELBW subjects and 126/145 (87%) control subjects is presented in Table 1. Neurosensory impairments were present in 41 (27.5%) ELBW children and included 1 or more of the following conditions: cerebral palsy (n = 19), hydrocephalus (n = 6), significant cognitive impairments (n = 14), autism (n = 5), unilateral blindness (n = 5), bilateral blindness (n = 9), and sensori-neural deafness (n = 2). Nine of these children had severe cognitive deficits and multiple impairments. One child was in a group home and 4 children were in foster care and the information on these children was obtained from their primary caregivers. Nonparticipants included 20 parents of ELBW subjects; of these 6 ELBW subjects had neurological impairments. The prevalence of neurosensory impairments was significantly lower among control children (control: 1.6%; P < .001). Nonparticipants included 19 parents of control subjects; only 1 of these children had a mild neurological impairment.

The majority of participating parents were mothers (ELBW: 85%; control: 93%). There were no significant differences in the mean ages of parents or in the distribution of social class²⁵ between the 2 groups. There were no significant differences in the parental demographic characteristics of participants and nonparticipants.

Health Status Assessment of Teenage Subjects by Parents

Based on levels of the 6 attributes of the HUI2 classification system, the health status of the 149 ELBW teenagers was described using 48 unique health states. In contrast, only 22 unique health states were used by 126 control parents to describe the health status of their children. Parents of ELBW subjects reported a lower proportion of teenagers as having no functional limitations (ie, perfect health), compared with control parents (34% vs 60%). One or 2 attributes were reported to be affected in 47% of ELBW subjects, compared with 39% of controls; 3 to 6 attributes were affected in 19% of ELBW teenagers, compared with 2% of control teenagers (² = 29.1; P < .0001).

Table 2 depicts the frequencies of disability (any level) for ELBW and control teenagers by attribute according to parental report. Statistically significant differences in the frequency distribution between groups were reported in the following attributes: sensation (P < .0001), mobility (P < .001), cognition (P < .001), and self-care (P < .04). There were no significant differences for emotion and pain attributes (P > .05). The proportion of children who had moderate to severe disabilities in each attribute is illustrated in Fig 1. A significantly higher proportion of ELBW teenagers was considered by their parents to have moderate to severe disabilities in sensation (P < .001), cognition (P < .0001), and self-care (P < .04) compared with controls. No significant differences were noted in the proportion with moderate to severe disabilities by parent report in the remaining 3 attributes (P > .05).

View larger version (12K): [in this window] [in a new window]   Fig. 1.   Parental assessment of teens' health status: proportion with moderate to severe disability by attribute. For the 6 attributes of HUI2 shown, levels 3 through 5 represent moderate or severe limitations.

There were no statistically significant differences in the general health of the teens as reported by parents of ELBW and control children: excellent in 56% of ELBW teens and 67% of control teens; good in 40% of ELBW teens and 31% of controls teens; fair in 4% ELBW teens and 1% control teens; and poor in 0% ELBW teens and 1% control teens (P = .14).

HRQL Ratings of Teenage Subjects By Parents

Own Child's Health State Table 3 shows the mean utility scores provided by parents when assessing their own children's health state. The mean utility score for ELBW teens was significantly lower than for controls (.91 vs .97; P = .002). The minimum score provided by ELBW parents was .10 compared with a minimum of .45 by control parents, and there was greater variability among ELBW parent scores (P < .01). The difference in variability is apparent from the difference in shapes of the frequency distributions for utility scores provided by parents of ELBW and control teens (Fig 2). A utility score of 1.0 (perfect health) was provided by 53% of parents of ELBW children compared with 72% of controls (P = .002). However, the ELBW distribution was more skewed with 4.2% of subjects having scores below .40 compared with none in this range among control parent respondents. Mean utility score of ELBW children with neurological impairments was .78 (standard deviation = .324), compared with .96 (standard deviation = .0865) for the health states of ELBW children without impairments (P < .0001).

View larger version (14K): [in this window] [in a new window]   Fig. 2.   Parental rating of the HRQL of their child on chance board: utility scores for the health states of ELBW and control children.

HRQL Ratings of Hypothetical Health States Table 4 provides summary statistics of parental utility scores for hypothetical health states. There are considerable similarities in the mean scores provided by parents of ELBW and control children for all hypothetical health states. Sandy and Pat, health states with the greatest disability, had the lowest mean scores and the variability was also greater than for the other 2 health scenarios. Intermediate scores were provided for Chris. Jamie, a child with learning difficulties, had the highest mean scores for the hypothetical scenarios.

Health States Worse Than Dead One parent of an ELBW child considered their own child's health state to be worse than dead. No control parents rated their child's health state to be worse than dead. A proportion of parents of both ELBW and control children reported some hypothetical health states (primarily Pat and Sandy) to be worse than dead on the chance board (ELBW parents: Sandy 39%, Pat 36%, other 5%; control parents: Sandy 31%, Pat 30%, other 4%). There were no significant differences in the proportion of parents who rated 1 or more hypothetical health states to be worse than dead, (ELBW: 48%; control: 42%; P > .05).

	DISCUSSION

Top Abstract Methods Results Discussion References

In many areas of child health, there is a growing trend to document parental perceptions of the health and developmental status of their children. Therefore, it is important to interpret our results in the context of the existing evidence. These studies suggest that when parents are asked the relevant questions in a clear and appropriate manner, they can provide data of moderate to high validity.^8-10 Parents are also the only source of information for developmental issues in young children and for those who are severely disabled and considered untestable by conventional measures.

In the field of neonatal intensive care, parents are being encouraged to play an active role in decision-making and to take the best interest of the infant and their family into consideration, at least where infants of borderline viability are concerned.^26,27 Yet, little is known about the impact of chronic medical problems and disabilities on the families or their personal perspective of the health status and quality of life of their children. This study was designed specifically to explore parental perceptions of the health status of their children and the values and preferences they place on the same health states.

Parents of ELBW children in this study reported a higher prevalence of functional limitations in most domains, and the severity and complexity of the limitations were also greater in comparison to reports by parents of control children. The limitations among ELBW survivors were found in the attributes that one would expect to be affected: vision, mobility, cognition, and self-care. Again, as expected, moderate and severe levels of disability in these attributes were reported more frequently for ELBW teens than for control teens. There is a tendency for researchers in medicine to perceive the control group as the "gold standard," with the expectation that they are normal in every respect. However, children in the control group in this study were not without problems. Although the actual neurological impairment rate was very low, they were also considered by their parents to have some degree of functional limitations in several domains.

We believe that the valuations provided by parents of ELBW children for the health states of their children were consistent to a large extent with the severity of their children's disabilities. For example, the overall mean scores assigned by parents of ELBW children were lower than those assigned by parents of control children, and fewer ELBW parents considered their children's health state to have utility scores equal to perfect health. The mean utility scores for children with neurological impairments were significantly lower than for those without impairments, and a proportion of ELBW parents reported utility scores below .40 compared with none by control parents. However, although parents of ELBW children reported a greater prevalence of disability, these differences were not necessarily associated with low utility scores.

The marked heterogeneity in utility scores provided by parents of ELBW and control adolescents in the current study is typical of data provided by all types of respondents to measurement surveys on HRQL. Such variations have been reported in studies on childhood cancer,²⁸ surveys on general population parents,¹⁹ self-reports by ELBW and control adolescents,²⁰ and within health professionals and other respondents.¹³ We have recently shown that health professionals provide lower mean utility scores for hypothetical health states than do adolescents and their parents.¹³ Although it is difficult to ascertain the reasons behind parental ratings of the HRQL of their own children, we found it interesting that parents of both ELBW and control children provided remarkably similar scores for the 4 hypothetical health states, and a similar proportion rated the severely disabled health states to be worse than dead. Quantification of states worse than dead provides an important additional perspective that may be useful in decisions regarding life-sustaining treatment and for estimating quality adjusted life-years. Patrick et al²³ suggest that such information should be incorporated into future studies on health services research and in medical decision-making.

The measurement of HRQL adds an important and meaningful dimension to the conventional biomedical approach of enumerating neurological impairments and other disabilities. Directly measured utility scores reflect a uniquely personal perception, so that it is possible for any 2 individuals to view the same health state very differently. It is this incorporation of values and preferences of individuals that distinguishes HRQL from all other measures of health.²⁹ The results of this study provide useful information on the relative preferences of parents for different health states. To our knowledge, no other investigators have obtained direct preferences from parents of premature children. Although Torrance et al²² and Boyle et al³⁰ were among the first to apply preference measures to assess the outcomes of neonatal intensive care, their study used preferences from a random sample of general population parents and parents of premature infants were not interviewed.

A valid concern about this approach, however, is that as yet we do not have clear knowledge of the processes by which individuals arrive at these judgements, nor the predictive validity of the same. Most studies are cross-sectional, and longitudinal data on the stability of preferences are very limited.^31,32 Concerns have been expressed by parents and physicians that the subjective ratings of HRQL obtained from children and parents may be inappropriately used to influence health policy decisions, and that additional validation, such as assessment by health professionals, is necessary before the preferences of patients can be accepted.^33,34 One has to accept that there is no single best perspective of HRQL and the unique information provided by relevant assessors should be respected. There does, however, seem to be a consensus that although patient and family preferences are important for individual clinical decision-making, community values are useful for program evaluation and for allocation of health-care resources.³⁵

This study adds to the information in the literature on parental perceptions of the health and functional abilities of their children. Similar to the study of high-risk children by McCormick et al,³⁶ most of the ELBW children were considered by their parents to have good to excellent general health even though many had significant functional disabilities. Parental perceptions are important in influencing the behavior and development of a child, because family coping patterns may foster a child's ability to function, despite ill health and disabilities. It has also been shown that parental assessment of their child's health has implications for the use of health services.³⁶

The relatively high valuation provided by parents of premature children for their children's health states, despite recognition of significant functional deficits, speaks highly of the resilience of parents in coping with disabilities. Perhaps with time, parents seem to accept their children's disabilities and to live with them and help their children to achieve their full potential. It may be easier for parents to accept what they know first hand about their own child's health state than conditions with which they have little or no experience. Therefore, the question remains whether the preference scores collected at adolescence are representative of the preference scores of parents had they been obtained in the neonatal period. In other words, are the preferences of individuals stable over time, or do other factors, such as life experiences, influence recaliberation of the same?^31,32 To address this type of question, we are currently obtaining preferences from high-risk women in the antenatal period and serially after the birth of the infant through the first year of life. The issue of stability of preferences requires additional resolution before parental preferences can be more formally incorporated in clinical decision-making during the neonatal period.

	ACKNOWLEDGMENTS

This study was supported by Grant 04447 from the Ontario Ministry of Health, Toronto, Ontario, and Grant HS-08385 from the Agency for Health Care Policy Research, Rockville, MD.

We are most grateful to the parents of premature and control children for their time and effort in assisting us with our ongoing studies. We thank Dr George Torrance (Health Utilities Inc) for his support and advice, Dr David Streiner for advice on statistical analysis, and Liz Merz for her help in tracing the subjects and typing the manuscript. The support of the Children's Hospital at Hamilton Health Sciences Corporation and the Department of Clinical Epidemiology and Biostatistics and the Center for Health Economics and Policy Analysis at McMaster University is gratefully acknowledged.

	FOOTNOTES

Dr Feeny is currently with the University of Alberta and Institute of Health-Economics, Edmonton, Alberta, Canada.

Drs Feeny and Furlong are currently with Health Utilities Inc, Dundas, Ontario, Canada.

Elizabeth Burrows is currently with Monash University, Melbourne, Australia.

Received for publication Dec 21, 1998; accepted Jun 29, 1999.

Reprint requests to (S.S.) McMaster University, Room 4G40, 1200 Main St W, Hamilton, Ontario, L8S 4J9, Canada. E-mail: saigal{at}fhs.mcmaster.ca

	ABBREVIATIONS

ELBW, extremely low birth weight; HRQL, health-related quality of life; HUI2, Health Utilities Index Mark 2.

	REFERENCES

Top Abstract Methods Results Discussion References

1. Lefebvre F, Glorieux J, St-Laurent-Gagnon T Neonatal survival and disability rate at age 18 months for infants born between 23 and 28 weeks of gestation. Am J Obstet Gynecol 1996; 174:833-838 [CrossRef][Medline]
2. Hack M, Friedman H, Fanaroff AA Outcomes of extremely low birth weight infants. Pediatrics 1996; 98:931-937 [Abstract/Free Full Text]
3. Saigal S, Szatmari P, Rosenbaum P, King S, Campbell D Cognitive abilities and school performance of extremely low birth weight children and matched term control children at age 8 years: a regional study. J Pediatr 1991; 118:751-760 [CrossRef][Medline]
4. McCormick MC, Brooks-Gunn J, Workman-Daniels K, Turner J, Peckham GJ The health and developmental status of very low-birth-weight children at school age. JAMA 1992; 267:2204-2208 [Abstract]
5. Szatmari P, Saigal S, Rosenbaum P, Campbell D Psychopathology and adaptive functioning among extremely low birthweight children at eight years of age. Dev Psychopathol 1993; 5:345-357
6. Hack M, Taylor HG, Klein N, Eiben R, Schatschneider C, Mercuri-Minich N School-age outcomes in children with birth weights under 750 g. N Engl J Med 1994; 331:753-759 [Abstract/Free Full Text]
7. Coplan J Parental estimate of child's developmental level in a high-risk population. Am J Dis Child 1982; 136:101-104 [Abstract]
8. Carey WB Validity of parental assessments of development and behavior. Am J Dis Child 1982; 136:97-99 [Medline]
9. Glascoe FP, Dowrkin PH The role of parents in the detection of developmental and behavioral problems. Pediatrics 1995; 95:829-836 [Abstract/Free Full Text]
10. Glascoe FP, Sandler H Value of parents' estimates of children's developmental ages. J Pediatr 1995; 127:831-835 [CrossRef][Medline]
11. Cadman D, Goldsmith C, Bashim P Values, preferences, and decisions in the care of children with developmental disabilities. Dev Behav Pediatr 1984; 5:60-64 [Medline]
12. Churchill DN, Torrance GW, Taylor DW, Measurement of quality of life in end-stage renal disease: the time trade-off approach. Clin Invest Med 1987; 10:14-20 [Medline]
13. Saigal S, Stoskopf BL, Feeny D, et al. Differences in preferences for neonatal outcomes among health professionals, parents and adolescents. JAMA. 1999;:281:1991-1997
14. Laine C, Davidoff F Patient-centered medicine: a professional evolution. JAMA 1996; 275:152-156 [Abstract]
15. Feeny D, Furlong W, Barr RD, Torrance GW, Rosenbaum P, Weitzman S A comprehensive multiattribute system for classifying the health status of survivors of childhood cancer. J Clin Oncol 1992; 10:923-928 [Abstract]
16. Feeny DH, Torrance GW, Furlong WJ. Health utilities index. In: Bert Spilker, ed. Quality of Life and Pharmacoeconomics in Clinical Trials. 2nd ed. Philadelphia, PA: Lippincott-Raven Press; 1996:239-252
17. Saigal S, Rosenbaum P, Stoskopf B, Comprehensive assessment of the health status of extremely low birth weight children at eight years of age: comparison with a reference group. J Pediatr 1994; 125:411-417 [CrossRef][Medline]
18. Saigal S, Feeny D, Furlong W, Rosenbaum P, Burrows E, Torrance G Comparison of the health-related quality of life of extremely low birth weight children and a reference group of children at age eight years. J Pediatr 1994; 125:418-425 [CrossRef][Medline]
19. Torrance GW, Feeny DH, Furlong WJ, Barr RD, Zhang Y, Wang Q Multiattribute utility function for a comprehensive health status classification system: Health Utilities Index Mark 2. Med Care 1996; 34:702-722 [CrossRef][Medline]
20. Saigal S, Feeny D, Rosenbaum P, Furlong W, Burrows E, Stoskopf B Self-perceived health status and health-related quality of life of extremely low birthweight infants at adolescence. JAMA 1996; 276:453-459 [Abstract]
21. Furlong W, Feeny D, Torrance GW, Barr R, Horsman J. Guide to Design and Development of Health-state Utility Instrumentation. Hamilton, Ontario: Centre for Health Economics and Policy Analysis, McMaster University; 1990. CHEPA Working Paper Series Paper 90-9
22. Torrance GW, Boyle MH, Horwood SP Application of multi-attribute utility theory to measure social preferences for health states. Operations Res 1982; 30:1042-1069
23. Patrick DL, Starks HE, Cain KC, Uhlmann RF, Pearlman RA Measuring preferences for health states worse than death. Med Decis Making 1994; 14:9-18
24. Torrance GW Social preferences for health states: an empirical evaluation of three measurement techniques. Socio-Econ Plan Sci 1976; 10:129-136 [CrossRef]
25. Hollingshead AB. Four Factor Index of Social Status. New Haven, CN: Department of Sociology, Yale University. Unpublished working paper, 1975
26. Fetus and Newborn Committee, Canadian Paediatric Society; Maternal-Fetal Medicine Committee, Society of Obstetricians and Gynaecologists of Canada Management of the woman with threatened birth of an infant of extremely low gestational age. Can Med Assoc J 1994; 151:547-553 [Abstract]
27. American Academy of Pediatrics, Committee on Fetus and Newborn, American College of Obstetricians and Gynecologists, Committee on Obstetric Practice Perinatal care at the threshold of viability. Pediatrics 1995; 96:974-976 [Abstract/Free Full Text]
28. Feeny D, Barr RD, Furlong W, Torrance GW, Weitzman S. Quality of life of the treatment process in pediatric oncology: an approach to measurement. In: Osoba D, ed. Effect of Cancer on Quality of Life. Boca Raton, FL: CRC Press; 1991:73-88
29. Gill TM, Feinstein AR A critical appraisal of the quality of quality-of-life measurements. JAMA 1994; 272:619-626 [Abstract]
30. Boyle MH, Torrance GW, Sinclair JC, Horwood SP Economic evaluation of neonatal intensive care of very-low-birthweight infants. N Engl J Med 1983; 308:1330-1337 [Abstract]
31. Everhart MA, Pearlman RA Stability of patient preferences regarding life-sustaining treatments. Chest 1990; 1:159-164
32. Llewellyn-Thomas HA, Sutherland HJ, Thiel EC Do patients' evaluation of a future health state change when they actually enter that state? Med Care 1993; 31:1002-1012 [Medline]
33. McCormick MC Follow-up studies, designs, analysis and reporting. Semin Neonatol 1996; 1:313-321 [CrossRef]
34. Harrison H Extremely low-birth-weight infants at adolescence: health status and quality of life. JAMA 1996; 276:1722 [CrossRef][Medline]
35. Gold MR, Patrick DL, Torrance GW, et al. Identifying and valuing outcomes. In: Gold MR, Siegel JE, Russell LB, Weinstein MC, eds. Cost-Effectiveness in Health and Medicine. New York, NY: Oxford University Press; 1996:82-134
36. McCormick MC, Athreya BH, Bernbaum JC, Charney EB Preliminary observations on maternal rating of health of children: data from three subspecialty clinics. J Clin Epidemiol 1988; 41:323-329 [CrossRef][Medline]