Research question
Systematically, and critically, review the methods (ie. study design, bias, confounding and chance) to assess the study quality and validity of the findings. The research paper is attached below from where we need to perform critical appraisal.
This is a critical appraisal of an article titled, ‘Acute effects of ambient temperature and particulate air pollution on fractional exhaled nitric oxide: A panel study among diabetic patients in Shanghai, China’, written by Li H, Bai H, Yang C, Chen R, Wang C, Zhao Z, Kan H., and published in the journal of epidemiology, 27(12):584-9, in the year 2017.
The research question being answered in this article is concerning the mechanisms involved in the air pollution by particulate matter in presence of ambient temperatures 1. To do this therefore, the researchers determined the association between fine and coarse particulate matter, and ambient temperatures during the fractional exhalation of nitric oxide, which is a biomarker of respiratory inflammation 2. This research question is valid and in line with the topic because the authors have linked the problem with previous research findings to show the existing gap. For instance, they acknowledge the fact that previous research has shown an existence of a link between temperature variations and air pollution by particulate matter in causing respiratory morbidities and mortalities. Since most of the respiratory tract infections are associated with inflammations, nitric oxide has been chosen as a non-invasive agent to access the mechanism of the association between ambient temperatures and particulate matter in respiratory tract infection 3.
This article has adopted a longitudinal panel research design among a study population of people suffering from type 2 diabetes mellitus in Shanghai, China. In this case, the authors justify the reasons of selecting a population of type 2 diabetes mellitus patients. In this case, they have argued that previous studies have indicated that these patients are highly vulnerable to the stimuli of ambient temperatures because they are in a state of high inflammation. The use of this study design fits to answer the research question because it involves making repeated observations on the same variables, either for a short or long period of time 4. Moreover, bearing in mind that this study involves the analysis of the effects of exposure of the type 2 diabetes mellitus patients to ambient temperatures and particulate matters, the actual relationship between exposure and effects must be presented. The longitudinal study design is most commonly used to test the cause-effect relationship between different variables. In this case, repeated measures of the association between ambient temperatures and particulate matter was followed up among the study participants throughout the study period. Moreover, this design allows the collection of both qualitative and quantitative data to allow for proper observation on exposure and outcomes relationship 5. However, this method is associated with drawbacks that would affect the completion of the research due to increased financial costs of this design requires. There could also be possibilities of interruptions during the follow-up of the study subjects leading to loss of follow-up across time.
Study design and sample
This study recruited 35 type 2 diabetes mellitus people from the urban communities in Shanghai China, among a population of 86,000 people. However, this study sample does not look quite representative of the population. This is because from a sample of 35 people, it would not be sensible enough to make a general conclusion about 86,000 people. Moreover, the authors have not presented the method used for the sample selection. It would be better if the selection method was indicated, alongside the equation for estimation of the sample size so that readers can understand how a sample of 35 type 2 diabetes mellitus patients was arrived at, and not any other figure 1. The inclusion of participants who had doctor-diagnosed type 2 diabetes was to ensure that only participants who were prone to respiratory tract infections as a result of exposure to ambient temperatures and particulate matter which is nitric oxide were recruited in this study. Moreover, the selection of people who had a permanent residence in the study area was to facilitate the ease of follow-up and prevent possible loss of follow-up which would in turn affect the final findings 6. In the selection of participants, the researchers excluded people who were active smokers, suffering from cardiac and pulmonary infections and alcohol drinkers. This is to rule out the possible respiratory tract infections and inflammation as a result of any other agents apart from ambient temperatures and particulate matter 7. This is because the named exclusion features are also known to cause infections to the respiratory tract.
Possible errors in this study could be during sampling whereby the sample size selected was so small as compared to the overall population of the study area. Therefore, this sample size might not be a representative of the concerned population 8. Selection error could also have occurred, whereby the issues of gender and age differences have not been highlighted.
The effect of confounding of variables is quite clear, by considering the two variables, ambient temperatures and particulate matter (nitric oxide). While low temperatures increase, the chances of bacterial and viral infection in the respiratory tract, the nitric oxide also causes inflammation of the respiratory tract. Therefore, there could be a possibility that the observed association between the two variables and inflammation on the respiratory tract could be due, totally or in part to these factors. Therefore, the effects of the confounding variables cause bias when estimating the impact of the exposures 9. This could for example indicate that there is a significant difference in the population, when in real sense no difference actually exists. Bias in this article could be due to loss of follow-up or the observer bias.
Possible errors and biases
This research can be classified as type two level of evidence study, since the randomized control trials fall in level one. This is because this was a longitudinal study involving follow-ups and repeated observations 10.
It could also be possible that the respiratory tract infections or inflammation which was observed was not due to the exposure variables but chance This is because, the viral infections could cause the inflammation due to the weakened immune system of type 2 diabetes mellitus patients and not an interplay between ambient temperatures and particulate matter. In this case, probably the use of healthy participants could rule out the issues of chance, in the obtained results.
This study was approved by the institutional review board at the school health in Fudan university 1. Application of ethical clearance is usually done before the research begins, which is the case that happened as outlined in this article 12. Before being granted ethical clearance, a research must demonstrate through detailed application, that the research will adhere to all ethical principles 13. Moreover, the study participants were asked to provide a written informed consent during the enrollment process. Seeking of informed consent was justified because in any research, more so those involving the use of human subjects, it enables the participants to choose on whether to participate or not 14. Consent also discloses the details of the research and the procedures to be used to avoid causing danger to them.
The statistical analysis involved the establishment of a link between exposure of the subject to nitric oxide, and the exact time when the test was performed. In this case, the mixed methods model was applied alongside the lag nonlinear model for short-term association between ambient temperature and the particulate matter exposure. The use of mixed methods in this case allowed the researchers to enable each and every study participant to serve as their own control for the adjustment of variations especially in longitudinal studies involving repeated measurements from the same subject during follow-ups. However, the use of the mixed effects model in research could suffer a number of drawbacks like the production of estimates which have high sample-sample variations that affects the final results. While the authors have provided various concepts in statistical analysis, they have also mentioned that the R software version 3.2.0, was used for data analysis, though no explanation is given for the choice of specifically this analysis tool. The choice of the relevant data analysis software is very important because it ensures that all variables are accurately analyzed and the data outputs obtained are sufficient to answer the initial research question.
Ethical consideration
Moreover, the article describes that the significance level was considered as p<0.05. The results for the ambient temperatures were presented in form of relative risk with respect to the nitric oxide by comparing with reference ranges. Additionally, the results for the particulate matter was presented in the form of percentages in the increase of nitric oxide based on their increasing concentrations. Therefore, the statistical analysis is clearly presented and this makes it easy for the readers to follow up the results manipulations with relative ease. The clinical significance is clearly illustrated in the results and discussion section of the article. This research reported that there were significant associations between the short term exposure to ambient low temperature conditions and the particulate matter of nitric oxide among patients suffering from type 2 diabetes mellitus in Shanghai China. This is because temperatures provide modifiers in analyzing the association between nitric oxide and particulate matter. Thus this article provides a clear epidemiological data and evidence concerning the effects of ambient low temperatures and inflammation to the respiratory tract. The clinical aspect of this is that the airway system is a body system which is affected by the stimulus from the physical environment. While previous epidemiological studies have indicated that the ambient temperatures and particulate matter causes mortalities and morbidities involving the airway system, the exact mechanisms were not provided before this research was performed. The link between the low temperatures and nitric oxide was because the exhaled nitric oxide is produced by a reaction involving the enzyme nitric oxide synthase 1. This enzyme is activated by internal mediators of the body like cytokines, or by the external factors like viral and bacterial infections. However, from literature, during cold weather, that is, low temperatures, there is high prevalence of both viral as well as bacterial infections, and these could possibly colonize the airways system and cause inflammations which lead to mortality and morbidity to the patients. This research clearly demonstrates both statistical as well as clinical significance of the research findings.
Publication bias occurs when the researchers choose to present and discuss the results which are clinically or statistically significant, while withholding other findings 15. For instance, in this article, the authors have not indicated whether there are some subjects who withdrew from the research during follow-ups, or whether there are those who died as a result of succumbing to type 2 diabetes and associated complications. Therefore, it is quite important for the researchers to appreciate the mechanisms of publication bias and other results-reporting methods so that they can minimize the negative impacts that could arise during the interpretation of results 16.
The internal validity in this research was achieved because the variables and experimental procedures were significant enough in answering the research question. The use of patients suffering from type 2 diabetes mellitus was to ensure that they were easily prone to respiratory inflammations upon the exposure to ambient temperatures and particulate matter, as compared to non-diabetic individuals. However, it is not indicated if a variable like age and sex could have effects on the severity and extent of inflammation. This would have been better explained so as to determine the age and gender intervals, if any, that could pose a higher risk to this exposure. At the same time, the manner in which the experiments were conducted followed clear procedures which can be easily replicated in different studies and hence valid enough. In this case, nitric oxide was chosen because it has been found to be non-invasive on human beings and hence suitable for use in the downstream experimental processes.
However, the external validity is not justified because the obtained results cannot be inferred to the general population in the study area due to the small sample size that was used 17. On the other hand, the results indicate the mechanism of the exposure and outcome of variables about these participants, a concept which was lacking in previous epidemiological studies. Therefore, the outcomes can be generalized, although the sample size of 35 out of the 86,000 people in the study area still raises some form of doubts about representability of the findings.
References
- Li H, Bai H, Yang C, Chen R, Wang C, Zhao Z, Kan H. Acute effects of ambient temperature and particulate air pollution on fractional exhaled nitric oxide: A panel study among diabetic patients in Shanghai, China. Journal of epidemiology. 2017 Dec 1;27(12):584-9. doi: 1016/j.je.2017.01.002
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