The study design was population-based cohort study with cross-sectional analysis. In the research, Gopinath et al. (2018) recruited 2856 adults aged greater than or equals to 49 years at baseline (for prevalence analysis) and 2037 adults for 15 year follow up (for incidence analysis). The prevalence and incidence analysis helped to ascertain the association between age-related macular degeneration and dietary intake of flavonoids.
Answer 1 (ii)
Independent variable of this study is flavonoids. Depended variable is age-related macular degeneration (AMD). This is because, the independent variable (flavonoids) is changed or controlled by the researcher and the effects of changing the independent variable is reflected on the dependent variable (AMD), the one which is measured (Hayes & Preacher 2014, p. 451).
Answer 1 (iii)
The main objective of the study is to access the independent association between the prevalence and 15-year incidence of AMD with the dietary intake of total flavonoids and common flavonoid (Gopinath et al. 2018, p. 1).
Answer 2 (iv)
First bias is confounding bias
Confounding bias because, the participants selected are either predisposes to AMD or consumes certain amount of flavonoids helpful in reducing the threat of AMD. So in this case, age and the previously known consumption of flavonoids is a confounder for the effect of total flavonoids on the development of AMD (Gopinath et al. 2018, p. 3).
Second bias is information bias
Information bias because, the participants were given self-administered food-frequency questionnaire (FFQ). This might increase the chance is systematic errors in measurement or misclassification of the exposure (Gouw et al. 2013, p. 232).
Answer 2 (v)
The scale of measurement used by implementing “9 category frequency scale” is interval scale. This is numeric scale used for statistical analysis. Since the data obtained are quantitative like first quartile, second quartile, third quartile and fourth quartile, the scale is quantitative and hence interval scale.
Answer 3 (i)
Incidence means rate of occurrence. That is number of individuals who develop AMD during older adult stage (Parisi et al. 2013, pp. 378).
Prevalence means total number of individuals in the population who have AMD at a specific period of time and is expressed in percentage of population (Parisi et al. 2013, pp. 378).
Answer 3 (ii)
Three factors controlled in the study include age, sex and covariates which is found to be associated with the incidence of AMD (smoking, consumption of fish and intake of zeaxanthin and lutein) (Gopinath et al. 2018, p. 3).
Answer 3 (iii)
Answer 4 (i)
0.63, 0.62 and 0.52 respectively (Gopinath et al. 2018, p. 4)
Answer (ii)
With the increase in the All flavonoids consumption, the odds ratio is decreasing therefore there is inversely proportional relationship. Thus the outcome is 48% less likely to develop AMD in the fourth quartile (Gopinath et al. 2018, p. 4).
Answer 4 (iii)
Odds ratio are used for measuring the association between a outcome and the preceding exposure (TchetgenTchetgen 2013, p.4570). Thus, reduction in the OR from the third to the fourth quartile indicates a less likely chance of AMD with intake of flavonols. Statistical significance refers to the likelihood of a relationship between variables being caused due to an event, in place of chance. Conversely, confidence interval refers to the range of values where the true value is present (Altman et al. 2013, p.552). Hence, 95% CI indicates 0.95 probability of comprising of the population mean .
Answer 4 (iv)
Statistical significance mean that upon increasing the intake of all flavonoids, the likelihood of onset of late AMD is low among people (Gopinath et al. 2018, p.1).
5 i) OR for total flavonones in the any AMD column, corresponding to the fourth quartile is 0.29. This indicates that the group shows a reduced likelihood of experiencing the particular event (AMD)(TchetgenTchetgen 2013, p.4569).
Answer 5 (ii)
The CI for the fourth quartile corresponding to total falvonones for any AMD is 95%. A 95% confidence interval comprises of a series of values that confirm 95% consistency of containing the actual mean of this population(Gopinath et al. 2018, p.4).
Answer 6 (i)
An inverse association is also referred to as a negative correlation and the term is used for explaining a contrary relationship between a dependent and an independent variable that are moving in opposite directions (Silbert et al. 2013, p.819). Thus, with an increase in the consumption of oranges that contain total flavonones, there was a reduction in the prevalence and/or incidence of AMD.
Answer (7)
The title of the newspaper article was accurate in stating that consumption of an orange every day plays an effective role in lowering the risks of onset of macular degeneration. This can be explained by the fact that in the research, 1 increase in standard deviation in the total amount of overall flavonoid was significantly related with lower risks of AMD (multivariable-adjusted OR: 0.76; 95% CI: 0.58, 0.99)(Gopinath et al. 2018, p.3). Thus, the news article was correct in establishing flavonoids present in oranges as the key component (Logan 2018).
The role of flavonoids in reducing oxidative stress and inflammation in the body was accurately presented owing to its impacts on enhanced vascular health(Gopinath et al. 2018, p.2). The article also focused on the drawbacks of the observational study.
This was explained in the research paper by the statement that the observational study failed to distinguish the impact of residual confounding from factors that were unmeasured such as, inflammatory markers(Gopinath et al. 2018, p.6).
Answer (8)
The Bradford-Hill criteria is given below (Fedak et al. 2015, p.14):
Answer 9 (i)
Prospective cohort and/or epidemiological studies need to be conducted
Answer 9 (ii)
Prospective cohort studies will follow similar individuals over a time frame and determine the changes in the dependent variable (AMD outcome) with respect to flavonoid consumption. Epidemiological investigation will establish a link between risk factor and the incidence of disease that is being investigated (AMD)
Answer 9 (iii)
Some of the challenges that might be encountered are as follows:
References
Altman, D., Machin, D., Bryant, T. & Gardner, M. eds., 2013, Statistics with confidence: confidence intervals and statistical guidelines, John Wiley & Sons.
Fedak, K.M., Bernal, A., Capshaw, Z.A. & Gross, S., 2015,‘Applying the Bradford Hill criteria in the 21st century: how data integration has changed causal inference in molecular epidemiology’. Emerging themes in epidemiology, vol.12, no.1, p.14,
Gopinath, B., Liew, G., Kifley, A., Flood, V.M., Joachim, N., Lewis, J.R., Hodgson, J.M. & Mitchell, P., 2018,‘Dietary flavonoids and the prevalence and 15-y incidence of age-related macular degeneration’, The American journal of clinical nutrition, vol.108, no.2, pp.381-387,
Gouw, S.C., Van Der Bom, J.G., Ljung, R., Escuriola, C., Cid, A.R., Claeyssens-Donadel, S., Van Geet, C., Kenet, G., Mäkipernaa, A., Molinari, A.C. & Muntean, W., 2013, ‘Factor VIII products and inhibitor development in severe hemophilia A’, New England Journal of Medicine, vol. 368, no. 3, pp.231-239. DOI: 10.1056/NEJMoa1208024
Hayes, A.F. & Preacher, K.J., 2014, ‘Statistical mediation analysis with a multicategorical independent variable’. British Journal of Mathematical and Statistical Psychology, vol. 67, no. 3, pp.451-470.
Logan, T 2018, ‘An orange a day keeps the macular degeneration away, early research finds’, ABC News, 18 July,
Parisi, R., Symmons, D.P., Griffiths, C.E. & Ashcroft, D.M., 2013, ‘Global epidemiology of psoriasis: a systematic review of incidence and prevalence’, Journal of Investigative Dermatology, vol. 133, no. 2, pp.377-385.
Silbert, B.I., Pevcic, D.D., Patterson, H.I., Windnagel, K.A. & Thickbroom, G.W., 2013,‘Inverse correlation between resting motor threshold and corticomotor excitability after static magnetic stimulation of human motor cortex’, Brain stimulation, vol.6, no.5, pp.817-820,
TchetgenTchetgen, E.J., 2013,‘Inverse odds ratio?weighted estimation for causal mediation analysis’. Statistics in medicine, vol.32, no.26, pp.4567-4580,
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