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Bias and Confounding in Public Health Research: Coffee and Hepatocellular Carcinoma

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Discuss the meaning of bias and confounding in relation to quantitative public health and health service research

The term bias is used to define the systematic error in the study of epidemiology, which makes the resulting output incorrect based on the assumptions of the research. Accordingly, this situation arises when there is a limited sample size or the following method in the study is not adequate to give the proper result of the research. However, this bias also impacted the whole research method and gives the wrong output by following the systematic error (Zhao et al. 2020). 50 different kinds of bias can impact the resulting output, among which, as per the opinion of the author, Leung et al. (2011), the bias that arises during the research is recall bias. However, the recall bias resulted in a lower or upper association between the outcome and the exposure. Along with that, it confounds the non-casual and true association between the outcome and the exposure. In this study, the author excluded people who are under medication and have a previous history of any kind of cancer.

Evaluate the steps taken by the author to minimise the bias and confounding

In the case of the confounder in the epidemiology study, it is the variable that can create an associational illusion among the other variables and can impact the outcome of the research result. However, to minimise the chance of bias, it is valuable that the researcher knows the confounders of the study. According to the viewpoint of the author, Sterne et al. (2022), the confounder in the research study is the main reason for the deformation in measuring the alliance between exposure and outcomes. However, the study is based on the impact of consuming moderate coffee on the health of a person and the chance of reducing the risk of "hepatocellular carcinoma in chronic carriers of hepatitis B". In addition, the factors of confounders are people who have a previous history of cancer, are under medication for liver diseases, are elderly, have smoking habits, consume tea and alcohol, and are also involved in physical activities. However, besides all the confounders selected by the author, the persons who are practicable in physical activity were found to be considerable confounders as they might consume such kinds of drinks, which can minimise observing the actual outcome of the research.

Along with that, the confounder, which is selected by the author of the study, is adequate in minimising the bias chances, as the author excluded all the individuals from the research sampling who could limit the study's outcome. However, the study was conducted on people who do not have any previous history of suffering from liver cancer or any kind of cancer and do not consume any other drinks other than coffee. According to epidemiological studies in the country where Japan banned Europe, 76% of the people who consume more than 5 cups of coffee a day have a lower risk of suffering from hepatocellular carcinoma. However, the involvement of confounders in the study minimises the chance of resulting in the actual outcome of a research, for which identification of confounders is effective in reducing the chance of bias (Zhao et al. 2020). In other words, the consumption of other drinks can minimise the actual outcome of the study, For this reason, the confounder which has been considered by the author here is appropriate in analysing the actual impact of drinking coffee in reducing the risk of hepatocellular carcinoma.

Identify the remaining sources of bias and confounding in the study that might still be open

selection of confounders and proper analysis of them before starting of the research is adequate to minimise their impact on the research result. However, during the conduction of the research, the author selected a small sample size, which is "234 HBV chronic carriers", according to the report, this sampling section is the main basis here. On the other hand, the author excludes some categories from the research for identifying the actual outcome of the study. Besides that, the study was conducted to evaluate the impact of consuming coffee at a higher level on the human liver and this consumption results in the reduction of hepatocellular carcinoma. In addition, the author considers gender as a confounder, however, in the paper, the female respondents of consume of coffee 5 times a day are 23 whereas the male respondent is 86. The study was conducted based on 234 respondents among which there is a minimum number of female candidates were chosen by the author. Further, the section of candidates might be a confounder for the study. In the country US there are approximately equal numbers of male and female citizens who consume coffee in a day more than 3 cups. Therefore it can be said that the selection of the sampling size and considering gender as a confounder might limit the actual outcome of the study.

Coffee consumption ratio in the US based on gender

Figure 1: Coffee consumption ratio in the US based on gender

Along with that, the author does not properly segregate the age group while sampling which resulted in a minimum number of respondents in this research who are under the age of 39. However, the age group is also a bias here which can impact the outcome of the study. Further, in this study, the author only considers the patients who are under medication for liver disease and does not have any previous record of suffering from cancer. However, other diseases are not considered in this research, such as the person who takes medicine for diabetes are not considered here. According to that the person who takes medicine for diabetes might consume coffee without sugar which can result in less effectiveness in preventing hepatocellular carcinoma by consuming coffee. Therefore it can be said taht the section of the confounder might be well in completing the study, however, there are some other confounders involved in the study.

Consider another study to determine the consumption of coffee can reduces the risk of "hepatocellular carcinoma in chronic carriers of hepatitis B"

Another study is considered here for comparison with the previous paper and also to find out the gap in the study of the author Leung et al. (2011). However, the paper of the author Kennedy et al. (2017) found adequate in analyzing the consumption of coffee's impact on human health. Along with that, the considered study is based on the examination of the association between caffeinated coffee and decaffeinated coffees impact on the human liver and its effectiveness in reducing the risk of hepatocellular carcinoma or HCC. Further, the sampling in the research is huge than the previous research which also works positively in analyzing the benefits of consuming coffee more than 5 times in a day. Accordingly, the author follows meta-analysis in this study which is also effective in identifying the actual outcome when there are various outputs depending on the same question (Pigott and Polanin, 2020).On the other hand, the author follows the PRISMA method for conducting the research which is considered well for reviewing reports in a systematic way, that is effective in computing the actual result.

Identify the pros and cons of the alternative study (400)

The first study which is here taken into consideration for identifying the impact of coffee consumption on reducing the risk of hepatocellular carcinoma has some limitations in finding out the actual outcome of the research. However, the mentioned confounder in this study creates limitations in demonstrating the actual results of the study. Accordingly, the second study here is considered for analyzing the gap in the previous study and also to find out proper measurement which can be adopted by the researcher for conducting the research in an appropriate way. However, the second study which is considered here has some pros and cons which is discussed here,

Pros of the study

The researcher selects a huge sample for conducting the research which is effective in segregating the sample size into different heads. However, for example with the help of the huge sample size the researcher can easily segregate the individual on the head of caffeinated coffee and decaffeinated coffee consumers. Accordingly, the researcher adopts the PRISMA methodology which is valuable in properly conducting a researcher with the help of systematic review. On the other hand, the researcher use the meta-analysis method which was not adopted by the previous researcher that also might be consider effective in find out the actual outcome of the research.

Cons of the study

In this study, the researcher mentions that there is a minimal impact of the confounder on the association of coffee consumption and HCC "hepatocellular carcinoma". However, the researcher did not properly mention the confounder for this study which can create bias. Accordingly, in this research paper, there is a minimum of examining the bias which is also not considered in analyzing research and also to demonstrate the outcome of the research in a proper way. On the other hand, the author adopts a valuable methodology for conducting the study, however, the did not properly mention the reason behind adopting the methods for conducting the study. Moreover, there are two variables taken into consideration by the author which are caffeinated and decaffeinated coffee, whereas the author does not consider the impact of consuming other drinks on reducing the risk of diseases. Therefore it can be said that this research might be appropriate for analyzing the importance of consuming coffee in minimizing the risk of HCC. However, the less consideration of confounders limited the study's selection for further comparison with previous research.

Evaluate the risk of hepatocellular carcinoma between the person who consumed coffee and who does not consume

Coffee consumption and the likelihood of carcinoma are highly associated. Based on the views of (McGlynn et al. 2021), coffee consumption is inversely connected with hepatocellular carcinoma and the liver cancer that is most commonly found. Therefore, caffeine has some chemo preventive properties present within the molecular segment. However, whether caffeine has any sort of association and responsible for the HCC still remains to be a question mark. It has been evidently examined that increasing consumption of coffee is associated with decreased risk of HCC. As per the reference of (Cheng et al. 2022), a reduced amount of risk has been found among females than men. As it has been identified that the consumption of coffee is considerably higher in women than men and has effectively decreased the chances and probability of the risk factors in men. It was around 54% less and men have a higher modestly reduced risk of HCC. More often, caffeine has been identified to inhibit “hepatic carcinogenesis” potentially by means of antioxidant radical and anti-inflammatory mechanisms.

The test of “strength of the association” has been evaluated with two examples and cases.


With hepatocellular carcinoma



Without hepatocellular carcinoma









Consume coffee



Consume coffee



Does not consume coffee



Does not consume coffee



Odds ratio



Table 1: Computation of ODD ratio

The above table represents the calculation of the ODD ratio for the identification of the increased consumption of coffee and treatment of HCC. It has represented the changes in the overall estimation of individuals and their level of coffee consumption that has effectively helped in identifying the probable risk of cancer HCCC. There are individuals the value of 209 that consume coffee has been 74 and those who do not consume coffee 135. On the other hand, there are 1583 individuals among them around 1257 consume coffee, and 326 that do not consume coffee. The computation of the ODD ratio has been done with the use of the formula “ “(A/B)/(C/D)” which is around 0.14. The ratio has helped in analyzing the results and analysis of coffee consumption among males and females and its impact on increased and decreased rates of HCCC. the conduction of the test basically represented the “strength of the association” within the two variables and its higher strength within them.


Aacrjournals.org (2023) Retrieved on 19th May 2023 from: https://aacrjournals.org/cebp/article/24/9/1398/155568/Coffee-Consumption-and-Risk-of-Hepatocellular

Cheng, H. Y., Lin, H. C., Lin, H. L., Uang, Y. S., Keller, J. J., & Wang, L. H. (2022). Association between nonselective beta-blocker use and hepatocellular carcinoma in patients with chronic hepatitis B without cirrhosis and decompensation. Frontiers in Pharmacology, 12, 3707. Retrieved on 19th May 2023 from: https://www.frontiersin.org/articles/10.3389/fphar.2021.805318/full

Kennedy, O. J., Roderick, P., Buchanan, R., Fallowfield, J. A., Hayes, P. C., & Parkes, J. (2017). Coffee, including caffeinated and decaffeinated coffee, and the risk of hepatocellular carcinoma: a systematic review and dose–response meta-analysis. BMJ open, 7(5), e013739. Retrieved on 19th May 2023 from: https://bmjopen.bmj.com/content/bmjopen/7/5/e013739.full.pdf

Leung, W.W.M., Ho, S.C., Chan, H.L., Wong, V., Yeo, W. and Mok, T.S., 2011. Moderate coffee consumption reduces the risk of hepatocellular carcinoma in hepatitis B chronic carriers: a case–control study. Journal of Epidemiology & Community Health, 65(6), pp.556-558. Retrieved on 19th May 2023 from: https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=fce9770af2d4d692d5c54835f57c698afa751d83

McGlynn, K. A., Petrick, J. L., & El?Serag, H. B. (2021). Epidemiology of hepatocellular carcinoma. Hepatology, 73, 4-13. Retrieved on 19th May 2023 from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7577946/

Pigott, T.D. and Polanin, J.R., 2020. Methodological guidance paper: High-quality meta-analysis in a systematic review. Review of Educational Research, 90(1), pp.24-46. Retrieved on 19th May 2023 from: https://journals.sagepub.com/doi/pdf/10.3102/0034654319877153

Sterne, J. A., Hernán, M. A., McAleenan, A., Reeves, B. C., & Higgins, J. P. (2019). Assessing risk of bias in a non?randomized study. Cochrane handbook for systematic reviews of interventions, 621-641. Retrieved on 19th May 2023 from: https://training.cochrane.org/handbook/current/chapter-25

www.statista.com (2023) Total coffee per capita consumption in the United States in 2020, by gender Retrieved on 19th May 2023 from: https://www.statista.com/statistics/457420/total-us-coffee-per-capita-consumption-by-gender/

Zhao, Q., Adeli, E., & Pohl, K. M. (2020). Training confounder-free deep learning models for medical applications. Nature communications, 11(1), 6010. Retrieved on 19th May 2023 from: https://link.springer.com/article/10.1007/s11111-019-0314-1

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