1. Aetna considers professional services for pediatric intensive feeding programs consisting of an inter-disciplinary team (e.g., behavioral therapist, occupational therapist, physician, registered dietitian, and speech language pathologist/therapist) to treat complex feeding and swallowing disorders in infants and children medically necessary when all of the following conditions are met:
   
   
   1. Behavior problems are interfering with feeding; and
   2. Diagnosis-specific treatment plan with child-specific interventions and estimated length of treatment are proposed and documented; and
   3. Medical causes of failure to thrive have been treated (e.g., acidosis, renal insufficiency, malabsorption) without resolution of the feeding problem; and
   4. Neurological or oral-motor problems exist; and
   5. Normal feeding milestones have not been met; and
   6. Physician will coordinate and oversee the treatment program; and
   7. Suboptimal score on nutritional assessment has been documented as indicated by any of the following:
      
      
      1. Weight below the 3rd or 5th percentile for gestation-corrected age and sex on more than one occasion.  Special growth charts for selected genetic syndromes should be used when indicated (e.g., for children with Down syndrome, Turner syndrome, etc); or
      2. Weight less than 80 % of ideal weight for age, using the standard growth charts of the National Center for Health Statistics (NCHS); or
      3. Depressed weight for length (i.e., weight age less than length age, weight for length less than10th percentile); or
      4. A rate of weight gain that causes a decrease in 2 or more major percentile lines (90th, 75th, 50th, 25th, 10th, and 5th) over time (e.g., from 75th to 25th); or

      5. A rate of daily weight gain less than that expected for age over the previous 2 months, and

   8. Unresponsive to initial treatment efforts by a single discipline (e.g., occupational therapist, speech language pathologist/therapist) over a 2-month period.

Aetna considers pediatric intensive feeding programs experimental and investigational for all other indications (e.g., childhood obesity, Prader-Willi syndrome) because their effectiveness for indications other than the ones listed above have not been established.

Outpatient care is appropriate for the majority of children with complex feeding problems.  Inpatient admission may be appropriate for management of acute problems in children who are severely malnourished (less than or equal to 75 % of ideal body weight), seriously ill, or at risk of harm. 

Notes:

1. Interventions for behavioral therapy are covered under the member's behavioral health benefits.  Please check benefit plan descriptions.
2. Some plans limit coverage of medically necessary speech therapy and occupational therapy.  Speech therapy of the developmentally delayed child has included training to improve the functioning of oral and pharyngeal muscles.  This oral-motor training is usually introduced before the emergence of speech.  Most Aetna plans exclude treatment of developmental delay.  Please check benefit plan descriptions for details. 
3. Aetna's policies typically exclude coverage for services, treatment, education testing, or training related to learning disabilities or developmental delays.  When the policy has such an exclusion, speech therapy and occupational therapy are not covered when the primary or the only diagnosis for a member is mental retardation or a learning disability such as a perceptual handicap, brain damage not caused by accidental injury or illness, minimal brain dysfunction, dyslexia, or developmental delay. 
4. Members should check their benefit plan descriptions for any applicable benefit plan limitations and exclusions on coverage for speech therapy services.

Standard growth charts of the National Center for Health Statistics (NCHS) are available at: http://www.cdc.gov/growthcharts/.

Pediatric feeding disorders should not be confused with anorexia or bulimia, which are characterized by marked disturbances in eating behavior more common in adolescence and adulthood.  For anorexia and bulimia, see CPB 0511 - Eating Disorders.

See also CPB 0049 - Nutritional Counseling, CPB 0061 - Nutritional Support, CPB 0116 - Frenectomy for Ankyloglossia, CPB 0226 - Hospitalization for the Initiation of Ketogenic Diet for the Treatment of Intractable Seizures, CPB 0243 - Speech Therapy, CPB 0248 - Fiberoptic Endoscopic Evaluation of Swallowing (FEES)/Fiberoptic Endoscopic Evaluation of Swallowing with Sensory Testing (FEESST), CPB 0250 Occupational Therapy Services, CPB 0625 - Dysphagia Therapy, and CPB 0648 - Pervasive Developmental Disorders.

Pediatric feeding disorders are a complex set of feeding and swallowing problems that disrupt the acquisition of age-appropriate feeding habits.  Feeding problems may include but are not limited to food refusal, disruptive meal-time behavior, rigid food preferences, suboptimal growth, and failure to master self-feeding skills commensurate with the child’s developmental abilities.  Feeding is a critical self help skill that develops during infancy and toddlerhood.  Inability to self- feed in toddlers or inability to be cooperative with caretaker feeding during infancy may result in severe functional limitation, thus contributing to or establishing disability. 

Children present for the evaluation and treatment of feeding and swallowing problems for a variety of reasons.  Feeding problems are estimated to occur in as many as 25 to 45 % of children with normal development, in 33 % of children with developmental disabilities, and in up to 80 % in children with severe or profound mental retardation (Silverman, 2010).  Approximately 50 to 67 % of children with feeding disorders present with mixed causes that include behavioral, physiological, and developmental factors.  The consequences of feeding problems can be severe and include: growth failure, susceptibility to chronic illness, and even death.  For a child to be diagnosed with feeding disorder of infancy or early childhood, the disorder must be severe enough to affect growth for a significant period of time.

Failure to thrive (FTT) is a term used to describe children, generally up to 3 years of age, who demonstrate a downward deviation in growth when compared to expectations from the standard growth charts of the National Center for Health Statistics (NCHS) Centers for Disease Control (CDC) growth charts.  It refers to infants whose weight is less than the norm for their gestation-corrected age, sex, genetic potential, and medical condition.  It does not include infants and young children with genetic short stature, constitutional growth delay, prematurity, or intrauterine growth restriction and who have appropriate weight for length and normal growth velocity.  The underlying cause of FTT is insufficient usable nutrition (i.e., inadequate intake or absorption, excess metabolic demand, or defective utilization).  Generally, growth failure is considered to be below the fifth percentile of weight and height for gestation-corrected age and sex when plotted on an appropriate growth curve (e.g., NCHS for children without genetic abnormalities, Down syndrome growth curve for children with Down syndrome, etc.) and who have decreased velocity of weight gain that is disproportionate to growth in length, taking into account appropriateness of size at birth.  Failure to thrive is not used to describe children growing along a curve with a normal interval growth rate, even if their weight is less than the 5th percentile.

There is no consensus regarding the definition of FTT, or how long a growth concern should exist before a child meets criteria for FTT.  However, the term may be attributed to a child who, with observation of growth over time, has any of the following:

• Weight below the 3rd or 5th percentile for gestation-corrected age and sex on more than one occasion.  Special growth charts for selected genetic syndromes should be used when indicated (e.g., for children with Down syndrome, Turner syndrome, etc); or
• Weight less than 80 % of ideal weight for age, using the standard growth charts of the NCHS; or
• Depressed weight for length (i.e., weight age less than length age, weight for length less than10th percentile); or
• A rate of weight gain that causes a decrease in 2 or more major percentile lines (90th, 75th, 50th, 25th, 10th, and 5th) over time (e.g., from 75th to 25th); or
• A rate of daily weight gain less than that expected for age.

Pediatric feeding problems are typically treated in outpatient settings by individual practitioners.  Some hospitals have developed comprehensive outpatient clinics with interdisciplinary care models called “pediatric intensive feeding programs” or “feeding clinics” that are designed to evaluate, diagnose, and treat children with severe or complex feeding and swallowing difficulties.  These interdisciplinary clinics are intended to provide greater environmental control, greater frequency of treatment, accelerated learning by increased contact with caregivers, and frequent medical and nutrition monitoring to provide clinicians with additional treatment options (e.g., appetite manipulation, swallow induction).  An interdisciplinary team of specialists work with the child and family to address the multiple factors involved with eating.  Programs vary across locations but generally focus on the feeding problems of infants and children up to 16 years of age.  The Kennedy Krieger Institute (Baltimore, MD) is an example of a facility that offers services ranging from outpatient assessment, intensive day treatment, and inpatient feeding programs that typically last about 8 weeks.  Key aspects of the program include direct observation behavior assessment, approaches for increasing and decreasing feeding behavior, skill acquisition, transfer of treatment gains, and parent training.

According to the recommendations of the American Academy of Pediatrics (AAP, 2010), screening for nutrition risks and problems is an expected part of routine preventive health services.  When the feeding problem is severe or complex, medical causes of FTT have been treated, and initial treatment efforts by a single discipline (e.g., occupational therapist, speech language pathologist) have failed, intensive treatment is considered.  A referral is made to an interdisciplinary team for assessment and intervention in order to evaluate and treat all factors influencing growth.  Services can include a comprehensive clinic evaluation, videofluoroscopic swallow study, feeding therapy, and family and caregiver education.  A nutrition assessment completed by a registered dietitian obtains information needed to rule out or confirm a nutrition related problem.  Nutrition assessment consists of an in-depth and detailed collection and evaluation of data in the following areas: anthropometrics, clinical/medical history, diet, developmental feeding skills, behavior related to feeding, and biochemical laboratory data.  During the assessment, risk factors identified during nutrition screening are further evaluated and a nutrition diagnosis is made.  The assessment may also reveal areas of concern such as oral-motor development or behavioral issues that require referral for evaluation by the appropriate therapist or specialist.  Other members of the interdisciplinary team may include behaviorists, occupational therapist, physical therapist, speech language pathologist/therapist, social worker, and home health care providers. 

Interventions are comprehensive and include behavioral modification to alter the child's inappropriate learned feeding patterns and parent education and training in appropriate parenting and feeding skills.  A majority of feeding problems can be resolved or greatly improved through medical, oral motor, and behavioral therapy.  Behavioral feeding strategies have been applied successfully even in organically mediated feeding disorders.  To avoid iatrogenic feeding problems, initial attempts to achieve nutritional goals in malnourished children should be via the oral route.  The need for exclusive tube feedings should be minimized. (Manikam and Perman, 2000). 

In many intensive treatment programs, the intervention involves 3 phases: (i) the child is fed directly by the therapist to establish a new set of feeding responses, (ii) parents are introduced into the feeding environment, and (iii) parents feed their child with clinicians coaching remotely. 

Common treatment objectives of the feeding team may include the following:

Pediatric psychologist: Provides a behavioral perspective on feeding disorders, assesses for co-morbid behavioral or psychiatric conditions within the child or family system, and provides interventions or facilitates referrals as appropriate.  Behavioral treatment strategies include implementation of meal-time structure and feeding schedule, appetite manipulation, behavior management, and parent training.

Physician: Monitors overall medical well-being of the child and provides oversight and support as needed while the child is in treatment.  Completes medical studies to identify and treat various physiological causes (e.g., endoscopy), manages various conditions through medication (e.g., medication for appetite stimulation, acid reflux therapy), and coordinates the broader treatment team.

Registered dietitian: Provides targeted nutrition interventions to improve growth (weight at or above 90 % of ideal body weight for length), improve growth velocity, increase nutrient intake, improve nutrient balance, redistribute calories from protein, carbohydrate, and fat, and help families avoid harmful foods/supplements.

Speech and language pathologist: Includes therapies to improve chewing and swallowing coordination, strengthen oral musculature, and improve oral tolerance to a broad range of flavors, textures, and temperatures of foods.

Most nutrition and feeding problems of children can be improved or controlled, but may not be totally resolved in complex cases.  Some children may require ongoing and periodic nutrition assessment and intervention.  Hospitalization may be neither helpful nor necessary unless the child is severely malnourished, seriously ill, or at risk of harm.  Separation of the child from the family by hospitalization may promote anxiety and anorexia in the child and cause a delay in feeding and supporting the child within his or her established environment (Kirkland and Motil, 2010). 

Indications for hospitalization include:

• Extremely problematic parent-child interaction
• Failure to respond to several months of out-patient management
• Precise documentation of energy intake
• Psychosocial circumstances that put the child at risk for harm
• Serious inter-current illness or significant medical problems
• Severe malnutrition (less than or equal to 75 % of ideal body weight)
• Significant dehydration.

A review of the literature on pediatric feeding disorders reveals the complexity involved in classifying feeding problems in infants and children.  The most frequently cited is the organic-nonorganic dichotomy.  Most feeding disorders have underlying organic causes; however, evidence indicates that abnormal feeding patterns are not solely due to organic impairment and that disordered feeding in a child is seldom limited to the child alone but is also a family problem.  Organic feeding disorders include problems related to structural abnormalities involved with feeding (e.g., anatomical defects of the palate, tongue, and esophagus), neuromuscular problems (e.g., cerebral palsy, paralysis), or other know physiologic reasons (e.g., esophagitis, gastroesophageal reflux (GER)) in which feeding can be disrupted.  In contrast, feeding disorders which are classified as having nonorganic origins include disruptive social and environmental circumstances.  Rarely can one reason or cause for feeding disorders be isolated or identified.  The most prominent medical diagnoses that can lead to feeding disorders include:

• Apraxia 
• Autism/Pervasive developmental disorders 
• Brain injury 
• Cardiac problems
• Cerebral palsy
• Children with tube feeding 
• Cleft palate 
• Constipation 
• Failure to thrive
• Feeding difficulties 
• Food allergies 
• Malabsorption 
• Muscular dystrophy 
• Neurological problems 
• Oral dysphagia 
• Prematurity 
• Reflux 
• Respiratory complications (e.g., pneumonia) 
• Short gut/bowel syndrome.

Burklow et al (1998) reported multiple characteristics associated with complex pediatric feeding problems and determined the relative frequency of each classification in a population referred to an interdisciplinary feeding team.  Written reports from team evaluations on 103 children (64 males, 39 females; age range of 4 months to 17 years) were reviewed.  Prematurity and/or presence of developmental delay were coded.  Identified factors related to current feeding problems were coded according to 5 categories: (i) structural abnormalities, (ii) neurological conditions, (iii) behavioral issues, (iv) cardio-respiratory problems, and (v) metabolic dysfunction.  Inter-rater reliability for the classification coding was 88 %.  Thirty-eight percent of the children had a history of prematurity and 74 % were reported to have evidence of developmental delay.  The following 5 categories or combinations were coded most frequently: (i) structural-neurological-behavioral (30 %), (ii) neurological-behavioral (27 %), (iii) behavioral (12 %), (iv) structural-behavioral (9 %), and (v) structural-neurological (8 %).  Overall, behavioral issues were coded more often (85 %) than neurological conditions (73 %), structural abnormalities (57 %), cardio-respiratory problems (7 %), or metabolic dysfunction (5 %).  The authors concluded that complex pediatric feeding problems are bio-behavioral conditions in which biological and behavioral aspects mutually interact and that both need to be addressed to achieve normal feeding.  In addition, the authors stated, "[e]mpirically validated treatment protocols specific to the constellation of problems present are needed to both increase effectiveness and reduce costs." 

The Washington State Department of Health (1998) examined the costs and benefits of nutrition and feeding team services for children with special health care needs in a case series of 30 children.  The children received services in the community, outpatient or home settings, and reflected a variety of medical conditions and congenital or genetic disorders.  Costs for the interventions provided and the interventions avoided were based on actual reported costs of providing these services in the community, or the costs were assigned uniformly, based on common practice in Washington State.  The children ranged in age from 11 days to 17 years, and had multiple visits over variable time periods within a variety of settings.  The estimated medical costs avoided exceeded the intervention costs for nutrition and feeding team services for 28 of the 30 children.  The ratio of intervention costs to medical costs avoided ranged from 1:0.8 to 1:20.  Positive outcomes for these children following nutrition or feeding team interventions included appropriate growth, improved dietary intake and adequacy, decreased illness and hospitalization, improved feeding skills and feeding behavior, and progress in feeding development.  The greatest improvements were in growth and dietary intake, which addressed the frequent initial problems of poor growth and inadequate diet.  The authors concluded that an investment in professional time with multiple family/child contacts can achieve improvements in nutrition and feeding problems and result in savings in overall health care expenditures.  Limitations of the study included (i) the case studies were not randomly selected, (ii) there was no comparison control population, and (iii) the specific cases did not necessarily represent all children with similar diagnoses. 

Schwarz et al (2001) reported the results of diagnostic evaluation and the effects of nutritional intervention on energy consumption, weight gain, growth, and clinical status in children (n = 79) with moderate to severe motor or cognitive dysfunction (male: female, 38:41; age, 5.8 +/- 3.7 years) who were referred for diagnosis and treatment of feeding or nutritional problems.  Initial assessments included a 3-day calorie intake record, videofluoroscopic swallowing study, 24-hour intra-esophageal pH monitoring, milk scintigraphy, and esophagogastroduodenoscopy.  These studies demonstrated GER with or without aspiration in 44 of 79 patients (56 %), oropharyngeal dysphagia in 21 (27 %), and aversive feeding behaviors in 14 (18 %).  Diagnosis specific approaches included GER therapy in 20 patients (25 %), fundoplication plus gastrostomy tube (GT) in 18 (23 %), oral supplements in 17 (22 %), feeding therapy only in 14 (18 %), and GT only in 10 (13 %).  After 25 months, relative calorie intake improved significantly.  The z scores increased significantly for both weight and height.  Improved subcutaneous tissue stores were demonstrated by increased thickness of both sub-scapular skin folds and triceps skin folds.  After nutritional intervention, the acute care hospitalization rate, compared with the 2-year period before intervention, decreased from 0.4 +/- 0.18 to 0.15 +/- 0.06 admissions per patient-year and included only 3 admissions (0.02 per patient-year) related to feeding problems.  The authors concluded that in children with developmental disabilities, diagnosis-specific treatment of feeding disorders resulted in significantly improved energy consumption and nutritional status and decreased morbidity (reflected by a lower acute care hospitalization rate) may be related, at least in part, to successful management of feeding problems. 

Rommel and De Meyer (2003) examined the complexity of feeding problems in infants and young children less than 10 years of age (n = 700) presenting to a tertiary care institution for severe feeding problems.  The first aim of the study was to characterize the etiology of feeding difficulties as medical, oral, or behavioral.  The second aim was to assess the prevalence of prematurity and dysmaturity in the patients and their relationship to the type of feeding problem.  Approximately 50 % of the children had a combined medical and oral condition underlying their feeding difficulties.  More than half of the children were examined for gastrointestinal conditions, particularly GER.  Behavioral problems were more frequently seen in children greater than age 2 years.  A significant relationship was found between the type of feeding problem and age: infants born preterm and/or with a birth weight below the 10th percentile for gestational age were at greater risk for developing feeding disorders.  Oral sensory-based feeding problems were found to be related to past medical interventions.  The authors concluded that a multidisciplinary team approach is essential for assessment and management of complex feeding problems in infants and young children because combined medical and oral problems are the most frequent cause of pediatric feeding problems.  In a review of the study by Rommel and co-workers, Gerarduzzi et al (2004) stated that (i) feeding disorders cannot be easily classified as organic or non-organic, (ii) their treatment requires a multidisciplinary approach, and (iii) careful attention should be given to early detection of causes that may be prevented.

Tufts-New England Medical Center conducted a systematic evidence review for the Agency for Healthcare Research and Quality (AHRQ, 2003) on the relationship between FTT and disability in children aged 18 years or younger.  The report concluded that evidence clearly suggests a relationship between FTT and concurrent disability, disability within 6 months, and disability beyond 6 months.  The report stated, "[t]here is substantial evidence that long term growth in all parameters (weight, height, and head circumference) of children with FTT compares unfavorably with thriving children and that this disparity persists even with appropriate attempts at intervention.  This pattern of a persistent growth deficit is seen in both developed and developing countries and across a wide spectrum of severity of FTT.  The effect on head growth is especially concerning, since increasing head circumference reflects brain growth, and therefore any impairment in head growth impacts neuro-developmental outcomes.  There is also evidence that the longer the growth failure continues, the less likely it becomes that treatment will be effective in reversing the negative long-term outcomes.  These findings highlight the importance of early identification and intensive nutritional intervention for children with FTT syndrome to improve efficacy of the therapy and to minimize long-term damage."  In addition, the report stated, "[a] consistent finding among these studies reviewed was the ineffectiveness of existing intervention programs.”

In a review of the literature on feeding problems of infants and toddlers, Bernard-Bonnin (2006) concluded that (i) feeding problems in early childhood often have multi-factorial causes and a substantial behavioral component, (ii) family physicians have a key role in detecting problems, offering advice, managing mildly to moderately severe cases, and (iii) more complicated cases should be referred to multidisciplinary teams.

A report by the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition on the nutrition support for neurologically impaired children (Marchand and Motil, 2006) stated, “[e]arly involvement by a multidisciplinary team of physicians, nurses, dieticians, occupational and speech therapists, psychologists, and social workers is essential to prevent the adverse outcomes associated with feeding difficulties and poor nutritional status.  Careful evaluation and monitoring of severely disabled children for nutritional problems are warranted because of the increased risk of nutrition-related morbidity and mortality.”

Lakeridge Health Corporation (Oshawa, ON, Canada), formerly Oshawa General Hospital, developed an interdisciplinary pediatric feeding and swallowing clinic in 1995.  Children ranged in age from birth to 16 years and have developmental delay, sensory integration difficulties, oral motor control problems, oral sensory problems, and/or poor weight gain and growth.  The interdisciplinary team consists of a pediatrician, a speech-language pathologist, an occupational therapist, and a registered dietitian.  A retrospective review to assess the performance of the clinic was performed on 104 subjects.  Goals were related to improvements in growth and/or feeding abilities and were individualized to each subject.  Initial goals were attained by the first follow-up visit in 75.9 % (95 % confidence interval: 70 to 81) of the subjects.  Progress in the clinic, as measured by the number of goals achieved by the first follow-up visit, was further analyzed according to the patient age group/category (i.e., infant, toddler, and child) and by the health care professional to ascertain and compare success rates in these groups and professionals.  The overall success rates in the patient age groups (p = 0.07) and among the different professionals (p = 0.92) were not significantly different.  The authors concluded that the interdisciplinary team approach proved successful in treating feeding problems in patients referred to the clinic.  Study limitations include: (i) possible inconsistency in documentation, (ii) potential variability in weight and height data collection techniques, (iii) ambiguous parental perception(s) about reporting progress, (iv) a possible lack of professionals’ goal standardization, (v) normal developmental outcomes during growth and development, and (vi) sample size and large variance limit the statistical analysis.  The authors stated that the results should be interpreted with caution and confirmed by further research with a larger sample size (Williams et al, 2006).

Schadler et al (2007) examined the long term outcome to therapy in a case series of 86 ex-premature infants with severe feeding disorders.  Children with a gestational age of less than 37 weeks referred for hospital rehabilitation because of severe feeding disorders, defined as tube feeding or average feeding times of more than 30 minutes were included.  Ex-premature infants accounted for 86/266 patients admitted for treatment of feeding disorders between 1995 and 2004.  The patients had the following diagnoses: cerebral palsy (41 %), mental retardation (51 %) and interaction problems (87 %).  The main element of treatment was behavioral therapy.  The authors reported a 62 % response rate at discharge.  Univariat analyses showed that tube feeding at admission and swallowing difficulties were the best predictors of failure to respond to the intervention.  Long-term follow-up data that were collected for 53 of the 86 children with similar initial response to therapy (64 %) compared to children with no follow-up data (58 %).  Success of therapy after discharge was maintained in 94 %; however, 25 % of the children with normal body mass indexes at discharge and sustained success of therapy fell below the 3rd body mass index percentile.  Cerebral palsy, mental retardation and interaction problems were found to be important risk factors for severe feeding disorders in ex-premature infants.  The authors reported that therapeutic intervention based on behavioral therapy achieved sustained success in almost two thirds of the children.

Greer et al (2008) investigated the impact of an intensive interdisciplinary feeding program on caregiver stress and child outcomes of children with feeding disorders across 3 categories: (i) tube dependent, (ii) liquid dependent, or (iii) food selective.  Outcomes for caregiver stress levels, child meal-time behaviors, weight, and calories were examined at admission and discharge for 121 children.  Repeated measures of analysis of variance were used to examine differences pre- and post-treatment and across feeding categories.  Caregiver stress, child meal-time behaviors, weight, and caloric intake improved significantly following treatment in the intensive feeding program, regardless of category placement.  The authors concluded that regardless of a child's medical and feeding history, an intensive interdisciplinary approach significantly improved caregiver stress and child outcomes.

In a report for the Washington State Department of Health on nutrition interventions for children with special health care needs, Latif et al (2010) stated, “[o]ften pediatric undernutrition and growth failure originate from multiple physical and psychosocial factors that change over time and are most effectively treated by an interdisciplinary team.”

There is some preliminary evidence of the effectiveness of selected clinical interventions to treat complex feeding and swallowing difficulties in infants and children (Miller, 2009).  While randomized controlled studies on the impact of pediatric intensive feeding programs on outcomes are needed, case studies indicate that an inter-disciplinary treatment approach to feeding disorders in complex cases offers the most comprehensive care for the treatment of these disorders and will likely promote the safest and most effective treatment plans (Silverman, 2010).