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2.2.1 Retrospective and Prospective Follow-up Studies

Follow-up studies of adults with developmental SLD date back to the 1960s and 1970s (Garvey 1970; Griffiths, 1969; Hall and Tomblin, 1978) and can be retrospective or prospective in their approach (Ruspini, 2002). Traditionally, follow-up studies have taken a retrospective approach. These are typically cross sectional meaning taken from a single point in time and studying a cohort once (as in (Aboagye, 2001; Records et al, 1992). In such studies the follow-up is the first and only time of data collection. For example, a cohort with a known history of SLD would be recruited as adults rather than recruiting children with SLD and tracking them through into adulthood. Some more recent studies have also been

retrospective in their approach (Aboagye, 2001; Records et al, 1992).

Other studies have used a prospective approach (Billstedt, Gillberg and Gillberg, 2005; Clegg et al., 2005; Conti-Ramsden, and Durkin, 2008; Johnson et al., 1999; Snowling et al., 2006). These are usually part of larger longitudinal studies that revisit the same cohort several times over the course of many years. Both methodologies have their strengths and weaknesses; these are summarised in table 2.1. Overall, prospective studies are significantly more difficult to carry out, but are ultimately superior to retrospective studies as they produce rich

longitudinal data sets.

The largest prospective studies are the National Cohort studies. These studies collect large and rich longitudinal databases on a national scale. The 1958 National Child

Table 2.1 - The advantages and disadvantages o f retrospective and prospective follow-up studies.

Retrospective studies Prospective studies Length of time Advantage - Relatively quick as

the cohort will only be visited once.

Disadvantage - Very slow,

projects could take the lifespan of the participants and researcher as cohort members will be seen multiple times over many years. Cost Advantage - Relatively cheap as

only 1 study will require funding.

Disadvantage - Relatively

expensive as multiple studies will require funding.

Workload Advantage - Relatively low as only 1 study will be carried out.

Disadvantage - Relatively high as many studies will be carried out. Larger longitudinal studies are typically carried out by large research teams or organisations. Attrition of the

sample

Advantage - No attrition as a cohort will be seen once.

Disadvantage - It is highly likely that increasing numbers of original cohort members will withdraw from a project over time.

Changing research interests

Advantage - None, as the study will be a snapshot and relevant to the research interests of the time.

Disadvantage - It is highly likely that the research interests will have changed by the end of a longitudinal project. This could mean a project will have different aims and focuses at different times as the knowledge in the field increases and theory progresses.

Longitudinal research questions

Disadvantage - Cannot address issues such as causality, risk factors or resilience with time.

Advantage - Can address issues such as causality, risk factors or resilience with time.

Examining the effects of age

Disadvantage - Difficult to

distinguish the effects of age from other factors.

Advantage - Can distinguish the effects of age as the same factors can be measured at a range of ages over the lifespan.

Data quality _{Disadvantage - May require} participants to recall things from the past. Some individuals may struggle with this and memories can become distorted with time.

Advantage - Will document participants’ life experiences of the time.

such data bases. The NCDS recruited everyone bom between the 3rd and 9th of March 1958 and collected information regarding their physical, psychosocial and educational progress in a series of follow-up studies at ages 7, 11, 16, 23, 33, 42 and 46 years. The BCS70 recruited children bom between the 5th and 11th of April and followed them up at ages 5,10,16, 26, and 30 years. Data was collected on their health, education, social and economic

circumstances (Schoon, Ross and Martin, 2007).

2.2.2 Psychometric Assessments

Psychometric assessments are quantitative test batteries specifically designed to measure performance within specific domains relative to normative data; examples of domains are cognitive, language or literacy. For example, the WASI- R (Wechsler, 1981) is designed to measure verbal and nonverbal IQ of ages 6-89. There are difficulties associated with their use: for example, they are typically standardised in 1 country; they can be subject

to performance on the day; and individuals can become familiar with assessment batteries with repeated exposure. Also most assessments designed to detect SLD are designed for children and the norms do not extend to adulthood. Thus such assessments may lack the sensitivity to detect more subtle difficulties which can persist into adulthood. In addition, they do not measure functional language such as that used in everyday situations. How to interpret psychometric assessments can also vary, for example when defining what identifies the presence of a difficulty; such as, the disagreement over the cut off point that distinguishes SLI from typical development (Rice, 2000) (previously discussed in 1.2.2). Even so,

psychometric assessments are commonly used in follow-up research (as in, Clegg et al., 2005; Johnson et al., 1999; Stothard et al., 1998).

2.2.3 Archive Data

Archive data can be utilised through document research and used to inform

retrospective follow-up studies. Documents can be written text, audio recordings or visual images and can have historical content (Bowling, 2002). The content of documents can be collected, coded, analysed and used to inform a research project. In a retrospective study documents have the advantage of capturing an earlier time point that the researcher wishes to study. This is unlike human memories that will become distorted with time (Ruspini, 2002) (see table 2.1). However, archive documents can be subject to biases imposed by their

original authors, and document research can be biased by the researcher’s interests that will influence what material might be selected.

A small number of follow-up studies have used archive data to help inform their findings (Aboagye, 2001; Schery, 1985; Shriberg and Kwiakowski, 1988). The method used by Aboagye (2001) was similar to the present project. She followed-up 4 ex-pupils of a residential special school for SLD and was able to use archive data from the ex-pupil’s time at the school to compare with her own data collected at follow-up for each of her case studies. Shirberg and Kwiakowski (1988) collated data from the school records of 55 children with special educational needs (SEN) and was able to map trajectories of their SEN between ages 4 and 8. Finally, Schery (1985) gathered data over an 8 year period for 718 with language

disordered children between the ages of 3;1 and 16;4 years. These data were organised into categories: demographics, physical development, social development, language and academic characteristics. From this the characteristics of the participants who showed the most progress could be drawn: for example the child’s age (the younger the better the outlook); nonverbal IQ; maternal education; clarity of child’s speech; behaviour and the child’s sociability.

2.2.4 Siblings as a Control Group

SLD can aggregate in families (Viging et al., 2003). A strong source of evidence for this comes from studies on the KE family. Gopnik and Crago (1991) collected data from 22 of the 30 members of this family spanning three generations; 16 of these participants had developmental dysphasia. The family members with dysphasia presented with grammatical errors in both expressive and receptive language. These errors indicated difficulties using plural forms and with tense markers. The family members without dysphasia did not show these errors. Examination of the KE family’s profiles suggested that some had caused by a specific deficit with learning language. This research eventually lead to the discovery of a gene for language known as FOXP2; a mutation which in this gene was thought to cause the severe language difficulties in the KE family (Lai, Fisher, Husrt, Vargha-Khadem and

Monaco, 2001). While this might seem like a breakthrough discovery, the idea that FOXP2 is really a gene for language and the cause of SLI was later treated with caution. Marcus and Fisher (2003) argued that it was just one genetic element that contributes to language

development and that it was unclear whether its role is special or unique; notably FOXP2 can be normal in many cases of SLI. Further research has suggested that SLI could also be

associated with genes on chromosomes 16 and 19 that potentially cause individuals to be at a genetic risk of developing SLI (The SLI Consortium, 2002).

Barry, Yasin and Bishop (2007) reported more difficulties with nonword repetition in parents of children with language impairment compared to those without language

difficulties; they argued that nonword repetition could serve as a marker of family risk for language difficulties. Tallal et al. (2001) also reported the risk of language difficulties to be significantly higher in families of probands with SLI than matched controls; mothers and fathers were equally affected but brothers were significantly more likely to be effected than sisters. There is now a consensus that language impairment can be inherited.

These findings question of the validity of using siblings and other family members as nonlanguage impaired controls in research into language difficulties. However, Clegg et al., (2005) successfully used siblings to control for upbringing and the family environment in their follow-up study of adults with DLD; siblings performed significantly better on language measures suggesting they were not affected by SLD (as described in 2.1.2). Pratt, Botting and Conti-Ramsden (2006) also reported that mothers of children with SLI were no more likely to have language difficulties than those in the general population. Overall this suggests that siblings can be used as a control group successfully, however the literature into family heritably suggests researchers should be cautious as family members may also have some level of SLD of their own. Psychometric assessment can help to confirm if this is the case.

2.2.5 Case Studies

Case studies and cohort studies are also complementary methodologies that follow-up research has utilised. A case study can be a detailed study of an individual, an organisation, a process, a neighbourhood, an institution or an event. Single or multiple cases studies can be examined by a research project (Yin, 2003). They allow detailed and rich data sets to still be drawn from only one or a few individuals.

Case studies in the follow-up literature have focused on individuals. Clegg and Henderson (1999) examined the economic outcomes for adults with persistent SLD. Within their cohort they were able to pick out the case of TH, a 34 year old male diagnosed with DLD in childhood. Aboagye (2001) is an example of a follow-up study that used 4 case studies to examine the outcomes of 4 adults with SLD in detail. The multiple case study design meant she was able to make direct comparisons between her cases. Studies of this type

have the advantage that they are able to provide a rich detailed data analysis of the research area that can include both quantitative and qualitative information. They have the

disadvantage that their findings are specific to those who participate, which limits their generalisability to other populations. As individuals with SLD are relatively few they can be challenging to locate and recruit; a case study design can therefore be advantageous when studying individuals with SLD as only small numbers need to be recruited.