IB Docs (2) Team
Research methods: genetics
Research methods in genetics
After completing this lesson, you should be able to:
- Identify two research methods used in genetic studies of behaviour
- Evaluate the strengths and limitations of the research methods
- Discuss the extent to which we can determine causality in genetic research
Before beginning this part of the module, take some time to revise the meanings of each of the following research methods. Can you describe the characteristics of each method - and its strengths and limitations?
- Case studies
- Correlational studies
- Experiments
- Natural experiment
- Quasi-experiments
One of the questions you may be asked on the IB exam is Discuss two research methods used in the study of genes and behaviour. For a lot of students, this is a tricky question. Up until now, this module has focused on techniques used to study genes and behaviour - not research methods.
Remember, when we talk about research methods, we are talking about experiments, observations, interviews, case studies, and correlational studies.
In this module (and in the textbook), we have looked at the following studies.
- Cai et al (2015)
- Caspi et al (2003)
- Kendler et al (2006)
- Kendler et al (2018)
- Weissman et al (2005) - see below
- Wender et al (1986)
Before anything else, please know that you do not need to know all of those studies! Please remember to fill in your online study guide to make sure that you are keeping organized for the final assessment.
However, when you look at this list, what do you think? What are the research methods used in the different studies above? When looking at genetic research in this module, there are three types of research that are commonly used: correlational studies, natural experiments, and case studies. For each of the studies above, see if you can figure out what the research method was. But before you take the quiz, read the following study by Weissman et al (2005). The researcher carried out a family study.
Weissman et al (2005) carried out a longitudinal family study with a sample of 161 grandchildren and their parents and grandparents to study the potential genetic nature of Major Depressive Disorder. The study took place over a twenty-year period, looking at families at high and low risk for depression. The parents and children were interviewed four times during this period. The children are now adults and have children of their own - allowing for the study of the third generation.
In order to establish credibility, researcher triangulation was used. Children were evaluated by two experienced clinicians - with one being a child psychiatrist and the other a psychologist.
Children had an increased risk of any disorder if depression was observed in both the grandparents and the parents, compared to children where their parents were not depressed. In addition, the severity of a parent's depression was correlated with an increased rate of a mood disorder in the children.
On the other hand, if a parent was depressed but there was no history of depression in the grandparents, there was no significant effect of parental depression on the grandchildren.
Checking for understanding
case study case study case study correlational study correlational study correlational study natural experiment natural experiment natural experiment natural experiment natural experiment
1. Cai et al (2015) was a .
2. Caspi et al (2003) was a .
3. Kendler et al (2006) was a .
4. Kendler et al (2018) was a .
5. Weissmann et al (2005) was a .
6. Wender et al (1986) was a .
1. Cai was looking at a correlation between a behaviour and the number of polymorphisms.
2. In Caspi's study, he wanted to see the effect of the IV - stressful life experiences - on individual with different genotypes. The individuals cannot be randomly allocated to conditions and the IV was not manipulated by the researcher.
3. Kendler's (2006) study was a twin study. This is correlational - he wanted to see if as genetic similarity increased, would we also see an increase in the concordance rate of the behaviour.
4. Kendler's second study was an adoption study. The placement of the children in either the home of the biological or the adoptive parent was the IV - which was not manipulated by the researcher.
5. Weissman is a longitudinal case study, involving researcher and method triangulation.
6. Wender is an adoption study - and is, therefore, a natural experiment.
In a natural experiment,
In a natural experiment, there is an independent variable but it is manipulated by "nature" - which could be the government, the weather, fate, etc.
One of the limitations of a natural experiment is
In a natural experiment, the researcher does not manipulate the IV. In addition, there is very little control over the study. This means that there is low internal validity as changes in the DV may have arisen due to extraneous factors. They are "natural", so ecological validity is usually high. Population validity is not dependent on the research method - but more on how the sample for the study was obtained. As for construct validity, this also is not related to the research method. It is how well the researcher has defined and measured variables. So, in studies of depression, it would be whether we can say that the measurement of "depressive symptoms" is a valid measure.
Which of the following is not true of correlational studies?
Because no independent variable is manipulated, cause and effect cannot be determined. In many cases, bidirectional ambiguity is problematic - for example, do women who have body dysmorphia read more fashion magazines, or do women who read more fashion magazines develop body dysmorphia? However, be careful of this argument in genetics. You cannot say, "Do the two short alleles lead to depression, or does depression lead to two short alleles?" We inherit our genome at birth and this does not change over our lifetime. What does change is gene expression.
Case studies may study
What is the advantage of a case study using researcher or method triangulation?
Using triangulation increases the credibility of the study. We know that the reason we got the results we did it not simply because we used a single research method - for example, an observation - because we got the same results in the same sample using different methods or by using different researchers.
One of the points that students often find confusing is that when carrying out the studies, the researchers used different data collection methods - such as an interview or questionnaire. An interview is only a research method when it is not used to gather data to be used for some other purpose - for example, to determine their history of past trauma so that it can be compared to their genotype - but instead when the data from the interview alone is used to draw a conclusion.
Assessment
One example of how a natural experiment is used in the study of genes and behaviour was done by Wender (1986). The researcher carried out an adoption study to test the role of heredity and environmental factors in major depression. In order to do this, they had two different groups. They had adoptees who suffered from depression -- and those that did not. They then compared the adoptees to both the mental health of their biological and their adoptive parents. Psychiatric evaluations of the relatives were carried out based on hospital records. The study found that depression was eight times as prevalent in the biological parents of adoptees with depression over the adoptive parents. This appears to indicate that genetics play an important role in the development of major depression.
Please now complete this part of the essay by adding a paragraph that explains why this is a natural experiment and evaluating the study.
Continue to Ethical considerations in genetic research
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