2021TrialExtended response

Q33 (g)

8 marks

Question

Rubella is an infectious disease caused by Rubivirus rubella. The disease is frequently mild, with a characteristic rash often appearing two weeks after exposure and lasting for three days. Other symptoms include fever, sore throat and fatigue, with joint pain common in adults. Up to half of infected cases are asymptomatic. Rubella is usually spread from one person to the next through the air via coughs of people who are infected. People are infectious during the week before and after the appearance of the rash. Only humans are infected. Once recovered, people are immune to future infections. In the early 1940s, Australian ophthalmologist Norman Gregg noticed a high incidence of congenital cataracts in babies whose mothers had suffered from rubella during pregnancy. It was then statistically shown that infection during early pregnancy may result in a miscarriage or a child born with congenital rubella syndrome (CRS). The main defects result almost exclusively from rubella infection occurring in the first 16 weeks of gestation and include deafness due to cochlea malformation, eye and cardiovascular defects and central nervous system damage leading to mental retardation. Rubella is preventable with a single dose of the rubella vaccine being more than 95% effective. When rubella vaccination became feasible around 1971, both the United States and the United Kingdom embarked on vaccination programs. In the United States, the strategy was to vaccinate infants, so that eventually the reservoir in childhood would be abolished. In contrast, the United Kingdom decided on a program of vaccinating adolescent girls. Both strategies were partial successes, in that CRS incidence began to decrease.

Evaluate the importance of validity in biological research. In your response, refer to:
• the study that you have described in part (f),
• ONE other named epidemiological study that you have investigated as part of your course
• ONE first-hand investigation that you have carried out as part of your course
• ONE second-hand investigation that you have carried out as part of your course

Uncropped source page 32 for question 33.g; requires human review and cropping — Reviewed visual · source page 32

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Solution

Criteria	Marks
• Demonstrates thorough understanding of validity.<br>• Correctly analyses own study, named epidemiological study, first-hand investigation and second-hand investigation.<br>• Evaluates the statement.	8
• Demonstrates good understanding of validity.<br>• Correctly analyses own study, named epidemiological study, first-hand investigation and second-hand investigation.<br>• Evaluates the statement.	7
• Demonstrates good understanding of validity.<br>• Correctly analyses three investigations or four with some omissions.	6
• Demonstrates sound understanding of validity.<br>• Analyses three investigations with some errors, OR demonstrates thorough understanding of validity.	5
• Demonstrates sound understanding of validity.<br>• Analyses two investigations, OR demonstrates good understanding of validity.	4
• Demonstrates some understanding of validity.<br>• Outlines validity of one investigation, OR demonstrates sound understanding of validity.	3
• Demonstrates some understanding of validity, OR outlines validity of one investigation.	2
• Provides some relevant information defining validity.	1

Additional guidance from the source:

Validity in a scientific investigation is extremely important as it describes whether the results of an investigation really do measure the concept being tested. In a firsthand investigation it includes whether the hypothesis is tested over a suitable range with appropriate equipment, if variables are controlled, if an experimental control is used when appropriate and if the method is suitable for testing the independent and dependent variables. For an epidemiological study, these address the issue of internal validity, which deal with bias, confounding effects and chance, while external validity addresses the ability to generalise the findings to a wider population. In a second-hand investigation it includes whether the information refers to the hypothesis being investigated, the data was gathered using an appropriate method and measuring devices, the findings are up to date as well as the nature of the article in terms of the credentials of the author, possible bias of the article and the nature of the publishing site (although this has been brought into controversy recently with a number of papers withdrawn from high impact journals). In the epidemiological study proposed, only unvaccinated pregnant women <16 weeks gestation with signs or symptoms of rubella infection were included. There was a control group, and randomly allocating patients to each group reduced any possible bias. There was no other medical care provided, which controls that variable. Blood levels of vitamin A and birth defects were measured using an appropriate technology as the independent and dependent variables. This gives this investigation a level of internal validity, but external validity would be less relevant as the results do not need to be extended to males, non- pregnant females. However, it may not extend to pregnancies in other ethnic groups. In the British Doctor’s Study, a prospective longitudinal cohort study, internal validity was ensured by following a large number of doctors (which reduced bias) and collecting accurate data regularly on the number of cigarettes smoked daily, health status and causes of death. As the doctors had to be registered in order to practice medicine, there was an unusually high level of follow-up in a study of this type. As this was not an experimental study, there is no need to have an experimental control. External validity could be questioned as younger subjects and females were excluded from the study due to lower numbers of health issues and subjects respectively. However, the results from this study have had significant impacts on public health policy around the world. In order to investigate the presence of microbes in water samples, validity was ensured by firstly testing different water samples (e.g. tap water, dam water and bottled water) for the presence of bacteria and fungi using appropriate procedures by inoculating agar plates, incubating them, counting the number and size of the colonies using a mm grid and identifying them by comparing them to reference images. Sterile processes such as running the inoculating loop through a flame were carried out to ensure that only the microbes in the water were tested. An experimental control was included with no water sample was performed, and variables such as composition of agar, temperature and length of incubation were controlled. When investigating the response of an Australian plant to a named pathogen, the validity of this second hand investigation was ensured by checking the source and content of the article studied. The information was published in a reputable peer-reviewed journal (Function Plant Biology), was recent (2017), written by a professor of Biology who had published in the area for more than 25 years and did not appear to be biased. As the plant investigated was an Australian native plant, and a number of immune responses such as H2O2 production, lignification and callose formation were described, it addressed the aim of the investigation. There are many aspects of an investigation which contribute to its validity, and it is important that they are all assessed to ensure that the investigation has addressed what it set out to address in order for the findings to be useful and relevant. Range: 1-8, average 3.7 Comments: Some students did not demonstrate their understanding of validity in their own investigations, particularly in their own second hand investigation.

Supplied marking guidance · human reviewed

Compare this with your working, not only your final sentence.

Syllabus alignment

Module 8 · Non-infectious Disease and Disorders

EpidemiologyEvaluate the method used in an epidemiological study.

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