Life expectancy following a cardiovascular event: In the ‘Selection’ category, the study scored the maximum of 4 stars. This was due to the representativeness of both the exposed and non-exposed cohorts, reliable ascertainment of exposure, and a clear demonstration that the outcome of interest was not present at the start of the study.
For ‘Comparability’, the study also scored the maximum of 2 stars. The research controlled for the most crucial factor, which was Type 2 Diabetes (T2D), and also controlled for several additional confounding factors.
Under ‘Outcome’, the study scored 2 out of 3 stars. It was given a star for objective assessment of outcome and another star for having a sufficiently long follow-up period. However, the study did not provide enough detail regarding the adequacy of follow-up cohorts to receive the third star in this category.
Overall, the study achieved a total NOS score of 8 out of 9. Despite not having a perfect score, the study appears to be of high quality based on the Newcastle-Ottawa Scale assessment. The study can improve by providing more detailed information about follow-ups and accounting for potential dropouts or lost participants.
| Criteria | Awarded Stars | Justification |
| SELECTION | ||
| Representativeness of the exposed cohort | ★ | Exposed cohort from CPRD database, representative of the general UK population (age, sex, ethnicity) |
| Selection of the non-exposed cohort | ★ | Non-exposed cohort also from CPRD, from the same community as the exposed cohort |
| Ascertainment of exposure | ★ | Exposure ascertained using CPRD medical codes from clinical practice |
| Demonstration that outcome of interest was not present at the start of the study | ★ | Exclusions made for those with prior diagnosis of CVD |
| Total Selection Score | 4★ | |
| COMPARABILITY | ||
| Control for most important factor | ★ | Controlled for T2D by creating exposed and unexposed groups |
| Control for any additional factor | ★ | Controlled for sex, IMD, lipid-lowering medication, smoking status, and pre-existing hypertension |
| Total Comparability Score | 2★ | |
| OUTCOME | ||
| Assessment of outcome | ★ | Outcomes assessed using linkage from CPRD, HES, and ONS Death Registration |
| Was follow-up long enough for outcomes to occur | ★ | Follow-up of 11 years (2007-2018) |
| Adequacy of follow-up of cohorts | Incomplete information about subjects lost to follow-up | |
| Total Outcome Score | 2★ | |
| TOTAL NOS SCORE | 8★ |
Post Cardiovascular Event Chances of Survival: Selection
Representativeness of the Exposed Cohort: 1 star – Justification: The exposed cohort in this study consisted of individuals with Type 2 Diabetes (T2D) identified from the Clinical Practice Research Datalink (CPRD). This is a large database that is considered representative of the general UK population in terms of age, sex, and ethnicity, thus making the exposed cohort representative of the average in the community.
Selection of the Non-Exposed Cohort: 1 star – Justification: The non-exposed cohort (those without T2D) were also drawn from the CPRD database, ensuring that it was from the same community as the exposed cohort.
Ascertainment of Exposure: 1 star – Justification: The exposure (T2D status) was ascertained using secure records in the form of CPRD medical codes, which are derived from clinical practice. This is a reliable and objective method of ascertainment, meeting the criteria for a star.
Demonstration That Outcome of Interest Was Not Present at Start of Study: 1 star – Justification: The study made clear exclusions for individuals who had a diagnosis code of Cardiovascular Event Disease (CVD), the outcome of interest, any time before the start of the study. This demonstrates that the outcome of interest was not present at the start of the study.
Total Selection Score: 4 out of 4 stars.
Comparability
Control for Most Important Factor: Yes (1 star)
Justification: The study has controlled for the most important factor, which is Type 2 Diabetes (T2D), the main independent variable of interest. The authors have controlled for this factor by creating exposed (with T2D) and unexposed (without T2D) groups and comparing the outcomes between these groups.
Control for Any Additional Factor: Yes (1 star)
Justification: The study has controlled for several additional potential confounding factors. These include sex, Index of Multiple Deprivation (IMD), lipid-lowering medication, current smoking status, and pre-existing hypertension. These factors were adjusted for in the statistical analyses.
Total Score for ‘Comparability of Groups’ Perspective: 2 stars (max 2)
Post Cardiovascular Event Chances of Survival: This score reflects that the study controlled for both the main factor of interest (T2D status) and additional potentially confounding factors in their study design and analysis. Thus, they have achieved the maximum score for the comparability of groups according to the Newcastle-Ottawa Scale.
Survival Chances Post Cardiovascular Event in Type 2 Diabetes: Assessment of Outcome:
Post-Cardiovascular Event Chances of Survival in Type 2 Diabetes
Post Cardiovascular Event Chances of Survival: The outcomes were assessed using record linkage, pulling from the Clinical Practice Research Datalink (CPRD), Hospital Episode Statistics (HES), and the Office for National Statistics (ONS) Death Registration data. This method is an excellent way of ensuring the objectivity of the outcomes.
• Independent blind assessment: [No]
• Record linkage: [Yes]
• Self-report: [No]
• No description: [No]
Cardiovascular Event: Was Follow-up Long Enough for Outcomes to Occur:
The follow-up was conducted over a period of 11 years, from January 1, 2007, to February 13, 2018. Given the outcomes under consideration (namely all-cause mortality following the first CVD event), this period is certainly long enough for the outcomes to occur.
• Yes: [Yes]
• No: [No]
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Cardiovascular Event: Adequacy of Follow-up of Cohorts:
While the study doesn’t provide exact details about the number of subjects lost to follow-up, it gives an account of subjects excluded due to various reasons. For example, it excludes individuals with no linkage to the HES or ONS, those who died before the study, had a diagnosis code of CVD before the study period, or with missing data on certain parameters. It also mentions the exclusion of individuals for whom no CVD events were recorded during the follow-up.
However, the study does not provide specific information about whether any subjects were lost to follow-up in the traditional sense (i.e., dropped out of the study, failed to continue reporting, moved away, etc.) or how this was handled. Hence, a star for this category cannot be given due to lack of complete information.
• Complete follow up – all subjects accounted for: [No]
• Subjects lost to follow up unlikely to introduce bias – small number lost: [No]
• Follow up rate and no description of those lost: [No]
• No statement: [Yes]
Post Cardiovascular Event Chances of Survival: In conclusion, based on the given information, the study scores 2 out of 3 in the “Adequacy of Follow-up” perspective. The detailed nature of the outcome measurement and the adequacy of the follow-up period are both strong points of this study. However, a complete account of the follow-up for the cohorts, specifically regarding subjects potentially lost to follow-up, would improve the robustness of the methodology further.
