Id |
Subject |
Object |
Predicate |
Lexical cue |
T223 |
0-30 |
Sentence |
denotes |
4.4 Strengths and limitations |
T224 |
31-190 |
Sentence |
denotes |
Our study is the first study to examine the association between long-term exposure to NO2 and PM2.5 and COVID-19 mortality at very high geographical precision. |
T225 |
191-489 |
Sentence |
denotes |
The spatial unit of our analysis is LSOAs, for which there are 32,844 in England (~130 000 km2), whereas previous studies have used 317 LTLAs or 175 sampling units in England, counties in the US (3 122 in an area ~9.8 million km2) and municipalities in the Netherlands (334 in an area ~41 500 km2). |
T226 |
490-659 |
Sentence |
denotes |
Such high-resolution allows capturing the localised geographical patterns of the pollutants but also ensures adequate confounding and spatial autocorrelation adjustment. |
T227 |
660-908 |
Sentence |
denotes |
Our study also covers, so far, the largest temporal window of the epidemic (capturing COVID-19 deaths attributable to the first wave, Supplemental Material Fig. S34), while most previous studies focused on the early to mid-stages of the first wave. |
T228 |
909-961 |
Sentence |
denotes |
This ensures better generalisability of the results. |
T229 |
962-1213 |
Sentence |
denotes |
In addition, physical distancing and other public health interventions were introduced nationwide in England during the first epidemic, mitigating any distortion between air-pollution and COVID-19 mortality due to potential regional level differences. |
T230 |
1214-1355 |
Sentence |
denotes |
Our results are also consistent in a sensitivity analysis focusing on the pre-lockdown period, in the absence of public health interventions. |
T231 |
1356-1526 |
Sentence |
denotes |
Based on the scientific literature, we adjusted for several variables which would act as the confounders of the relationship between air pollution and COVID-19 mortality. |
T232 |
1527-1717 |
Sentence |
denotes |
Nevertheless, since the aetiology and the factors contributing to COVID-19 mortality are not fully understood yet, we included a spatial random effect to capture unknown spatial confounding. |
T233 |
1718-1793 |
Sentence |
denotes |
The spatial random effect was found to be a crucial component in the model. |
T234 |
1794-1984 |
Sentence |
denotes |
Not accounting for spatial autocorrelation, when spatial autocorrelation is present, is expected to give rise to narrower credible intervals and false positive effects (Lee and Sarran 2015). |
T235 |
1985-2021 |
Sentence |
denotes |
Our study has also some limitations. |
T236 |
2022-2100 |
Sentence |
denotes |
The downscaling procedure will likely inflate the reported credible intervals. |
T237 |
2101-2215 |
Sentence |
denotes |
However, this naturally reflects the uncertainty of the place of residence resulted from the downscaling approach. |
T238 |
2216-2373 |
Sentence |
denotes |
Although we consider small areas, the study is still an ecological one and thus the reported effects do not reflect individual associations (Wakefield 2008). |
T239 |
2374-2505 |
Sentence |
denotes |
Case fatality might have been a more appropriate metric for the analysis, since disease spread is accounted for in the denominator. |
T240 |
2506-2720 |
Sentence |
denotes |
Nevertheless, given the asymptomatic infections and the fact that number of reported infections is not a random sample of the general population, the number of COVID-19 cases per LTLA is not reliable at this stage. |
T241 |
2721-2930 |
Sentence |
denotes |
For the same reason, using the number of reported cases to adjust for disease progression and clustering of cases and deaths might not adequately capture disease progression and clustering of cases and deaths. |
T242 |
2931-3013 |
Sentence |
denotes |
However, part of this clustering was captured in the spatial autocorrelation term. |
T243 |
3014-3150 |
Sentence |
denotes |
We did not account for population mobility during 2014–2018 and assumed constant residence and thus levels of exposure to air-pollution. |
T244 |
3151-3412 |
Sentence |
denotes |
While this is a limitation, we believe that it would have a minimal impact on the results given that 1) the exposure period is relatively short and 2) almost 93% of the deaths in our dataset occurred in people 60 years or older (Supplemental Material Table S2). |
T245 |
3413-3517 |
Sentence |
denotes |
This comprises a population less likely to have moved during the past 5 years (Burgess and Quinio 2020). |
T246 |
3518-3587 |
Sentence |
denotes |
We also could not account for non-residential air-pollution exposure. |
T247 |
3588-3852 |
Sentence |
denotes |
Spatiotemporal variation in the strains of COVID-19 can introduce bias (Villeneuve and Goldberg 2020), however at the time of publication there was no evidence supporting that strain types can confound the relationship between COVID-19 mortality and air-pollution. |