Question

A disruption of a gene called \(D Y X C 1\) on chromosome 15 for humans may be related to an increased risk of developing dyslexia. Researchers \({ }^{16}\) studied the gene in 109 people diagnosed with dyslexia and in a control group of 195 others who had no learning disorder. The \(D Y X C 1\) break occurred in 10 of those with dyslexia and in 5 of those in the control group. (a) Is this an experiment or an observational study? What are the variables? (b) How many rows and how many columns will the data table have? Assume rows are the cases and columns are the variables. (There might be an extra column for identification purposes; do not count this column in your total.) (c) Display the results of the study in a two-way table. (d) To see if there appears to be a substantial difference between the group with dyslexia and the control group, compare the proportion of each group who have the break on the \(D Y X C 1\) gene. (e) Does there appear to be an association between this genetic marker and dyslexia for the people in this sample? (We will see in Chapter 4 whether we can generalize this result to the entire population.) (f) If the association appears to be strong, can we assume that the gene disruption causes dyslexia? Why or why not?

Short answer

This is an observational study and the variables are dyslexia status and \(D Y X C 1\) gene break status. The data table will have 2 rows and 2 columns. There seems to be a higher association of the \(D Y X C 1\) gene break with dyslexia, but causality cannot be concluded based on this data.

Step-by-step solution

Is it an experiment or an observational study?

This is an observational study. Research was done by looking at the existing data from dyslexic patients and a control group. The variables are the presence or absence of the \(D Y X C 1\) gene break and whether the individual has dyslexia or not.

Rows and Columns

The total number of rows will be two (one for subjects with Dyslexia and one for the control group). The amount of columns is two as well (people with the \(D Y X C 1\) break and people without the \(D Y X C 1\) break).

Two-way table

Let’s construct a two-way table with dyslexia status on the rows and \(D Y X C 1\) break status in the columns. In each cell, the count of people belonging to that category will be displayed. For example, there are 99 people in the dyslexia group that do not have a \(D Y X C 1\) break and 195-5=190 people in the control group that do not have a \(D Y X C 1\) break.

Comparison of proportions

To compare proportions, calculate the proportion of each group who have the \(D Y X C 1\) gene break. For the dyslexia group, this is 10/109 and for the control group, this is 5/195.

Association

Judging from the proportions above, there does appear to be a higher association of the \(D Y X C 1\) gene break with dyslexia. However, we need to do further statistical testing, for example using a Chi-square test, to be sure.

Causality

While there may be an association between the gene disruption and dyslexia, one cannot conclude causality based on this data. This is because it is an observational study; there could be lurking variables or the gene break could be an effect rather than a cause of dyslexia. To establish causality, further detailed studies are required, preferably randomised controlled trials (if ethically sound).

Key concepts

Observational Study

When studying the relationship between the DYXC1 gene and dyslexia, researchers carried out what is known as an observational study. Unlike experiments, where scientists manipulate variables and observe effects, observational studies involve no such interference. Instead, researchers observe and record data as it naturally occurs. This often means they look at real-world scenarios where factors are outside their control. In this case, the variables were whether or not individuals had a certain gene disruption and whether they were diagnosed with dyslexia. The strength of observational studies lies in their reflection of genuine, unaltered conditions, but this very feature limits their ability to determine cause-and-effect relationships. Hence, they are paramount in establishing associations that might warrant further experimental research.

DYXC1 Gene

The DYXC1 gene is under scrutiny due to its suggested link to dyslexia, a learning disorder characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities. This gene is one out of several that has been of interest because of its potential contribution to this condition. Genetic studies, like the one outlined in the exercise, aim to elucidate whether the presence or alteration of such genes is related to the manifestation of dyslexia. While the data indicates a higher occurrence of the gene disruption among dyslexic individuals compared to the control group, conclusions must be drawn cautiously, as it is only a piece of the complex puzzle that is the genetics of dyslexia.

Association vs Causality

Understanding the nuance between association and causality is fundamental in scientific research. An association indicates a link between two variables—here, we see a potential link between the DYXC1 gene break and dyslexia. However, proving causality, the notion that one event is the direct result of another event, is much more challenging. Why might this be? In our given data, even a strong association does not rule out the possibility of other factors, known as confounding variables, influencing the results. Therefore, while the initial study shows an association, it cannot claim that the DYXC1 gene disruption causes dyslexia without comprehensive, controlled experimental studies designed to isolate the effect of this gene.

Two-Way Table

A two-way table is a statistical tool used to display the frequency of different combinations of two categorical variables. In our exercise, the two-way table is used to organize the presence of the DYXC1 gene break against the diagnosis of dyslexia. Each cell within the table represents the count of individuals that correspond to each combination of variables—those with dyslexia and the gene break, those with dyslexia without the gene break, and so on for the control group. This visual representation helps us to quickly assess potential associations between the variables in question and is a common and practical method in educational research to simplify complex data sets.

Educational Research Methods

The methodologies encompassed by educational research methods are indispensable when seeking answers to questions about how we learn and how educational approaches might be improved or restructured. They include quantitative methods like the one used in the dyslexia genetics study which involves numerical data and statistical testing to decipher patterns and associations. Similarly, qualitative methods, such as interviews or case studies, provide more detailed narratives and a deeper understanding of participants' experiences. To design effective education strategies that cater to diverse needs, researchers often combine multiple methods. This combined approach might be particularly beneficial when exploring the complexities of conditions like dyslexia, where a multidimensional understanding is key to creating supportive learning environments.