Having established that there are serious negative consequences associated with all types and severities of hearing loss, a natural question is whether there are significant benefits to the child if hearing loss is identified early and appropriate intervention is begun. It is important to note that there have not been prospective randomized clinical trials addressing that issue (slide #51). Most of the evidence we have can be criticized or is weakened by the fact that there is potential for selection bias, most studies do not include long-term follow up, sample sizes are generally quite small, and in some of the studies the types of outcomes assessed were somewhat subjective.
In spite of those weaknesses, there is a fair amount of information showing that there are benefits associated with earlier identification and intervention. For example, a study reported by Yoshinaga-Itano and her colleagues in 1996 (slide #52) evaluated the language abilities of 46 children with bilateral hearing loss identified before 6 months of age, with 63 similar children identified after 6 months of age. Language abilities were measured by parent report using a cross-sectional assessment design in which children were categorized into four different age groups. As can be seen in slide #53, the 23 children assessed when they were 13-18 months old already showed an advantage for the earlier identified group. This advantage for the earlier identified group becomes larger for the 28 children assessed when they were 19-24 months of age, larger still for the 31 children assessed when they were 25-30 months of age, and even larger for the 27 children assessed when they were 31-36 months of age. As shown in slide #54 and slide #55, the results are similar for measures of expressive language and vocabulary.
Apuzzo and Yoshinaga-Itano reported a similar study in 1995 (slide #56) in which 69 children with hearing impairment were categorized into four groups according to the age of identification. Groups were reasonably similar with respect to age at the time of testing, degree of hearing loss, and level of development. All of the children were participating in similar early intervention programs, but had began at different ages. Outcome data are based on parent report using the Minnesota Child Development Inventory, and results shown in slide #57 are based on covariance adjustments for degree of hearing loss and cognitive ability. As can be seen, the 14 children identified earliest are functioning almost at grade level, while those identified latest (25+ months) are functioning at substantially lower levels.
Another study conducted by Sue Watkins at Utah State University (slide #59) provides similar information, but the design is stronger because all of the children were assessed at the same time, sample sizes are larger for each group, and there was more extensive matching and statistical adjustment for potential confounding variables. In this study, there were three groups of 23 children who had been matched or the scores were statistically adjusted for a variety of variables, including severity of hearing loss, age, presence of other handicap, age of mother, SES indicators, and number of childhood middle ear infections. The first group had received an average of nine months of home intervention before 30 months of age, and then received preschool intervention until they were enrolled in public school. The second group of children received no home intervention, but began a preschool intervention program at 36 months of age. The third group received no home intervention or preschool intervention.
A wide variety of measures were collected by trained diagnosticians who were unaware of the group to which the children belonged. As shown in slide #59, it is clear that those who received both home-based intervention and preschool intervention did substantially better than those who received only preschool intervention or did not receive any intervention prior to beginning public school. The effects for reading, arithmetic, vocabulary, articulation, percent of the child's communication understood by non-family members, percent of non-family communication understood by the child, social adjustment, and behavior shows that children who received the most intensive early intervention perform 20-45 percentile points higher than children who do not receive such intervention. The results of this study are particularly convincing because:
- all of the children received the same types of intervention from the same providers, except that they were enrolled in intervention programs at different ages;
- the diagnosticians were unaware of the group to which children belonged;
- matching and/or statistical adjustment was done on a wide variety of variables; and
- measures covered various domains and were collected when children were 10 years old.
Even though results of randomized clinical trials are not available to address the question of whether earlier intervention is better than later intervention for children with hearing loss, the consistency of findings from a number of quasi-experimental studies provides consistent and convincing evidence about the benefits of earlier intervention. It is important to note that the type of intervention children need is dependent on the type and severity of hearing loss (slide #60). Because it has only been in recent years that we have identified children with unilateral and mild bilateral losses at less than one year of age, we do not have a great deal of experience about how to provide the most effective intervention to these children. Over the next several years, as we gain more experience in providing intervention to children in these groups, we will learn more about how to deliver intervention most effectively. As more and more children are identified at earlier ages, it is also expected that more data about the benefits of early intervention will become available.
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