Statistical analyses of case-control studies - Pubrica
                     STATISTICAL 
ANALYSES  OF CASE-
CONTROL  STUDIES
An Academic presentation by
Dr. Nancy Agnes, Head, Technical Operations, Pubrica 
 Group: www.pubrica.com
Email: [email protected]
Today's Discussion
Outline Introduction
Advantages and Disadvantages of Case-Control 
Studies  Study Design
Selection of Case  
Selection of a 
Control  Matching
Data 
Collection  
Analysis
Risk Factors 
and 
Sampling
Recent Research on Case-Control Studies using Statistical 
Analyses  Conclusion
Introduction
A case-control study is used to see if exposure is  
linked to a certain result (i.e., disease or condition of  
interest).
Case-control research is always retrospective by  
definition since it starts with a result and then goes  
back to look at exposures.
The investigator already knows the result of each  
participant when they are enrolled in their separate  
groups.
Contd...
Case-control studies are retrospective because of  
this, not because the investigator frequently uses  
previously gathered data.
This article discusses statisticalanalysis in
case-  control studies.
Advantages and Disadvantages of 
Case-  Control Studies
Contd...

Study  
Desig
Participants in a case-control study are chosen for n
 the study depending on their outcome status.
As a result, some individuals have the desired  
outcome (referred to as cases), while others do not  
have the desired outcome (referred to as controls).
After that, the investigator evaluates the exposure in  
both groups.
Contd...
As a result, in case-controlresearch, the outcome must occur in at
least  some individuals.
Thus, as shown in Figure 1, some research participants have the outcome, 
 and others do not enrol.
Contd...

Selectio
n  of 
Case The cases should be defined as precisely as feasible by  
the investigator.
A disease's definition may be based on many criteria at  
times; hence, all aspects should be fully specified in the  
case definition.
Selection 
Controls that are comparable to the cases in a
variety of ways should be chosen. The matching  of a  
criteria are the parameters (e.g., age, sex, and  Control
hospitalization time) used to establish how controls  
and cases should be similar.
For instance, it would be unfair to compare patients  
with elective intraocular surgery to a group of  
controls with traumatic corneal lacerations.
Another key feature of a case-control study is that 
 the exposure in both cases and controls should be  
measured equally.
Matching
Though some controls have to be similar to cases in 
 many respects, it is possible to over-match.
Over-matching might make it harder to
identify  enough controls.
Furthermore, once a matching variable is chosen,
it  cannot be analyzed as a risk factor.
Contd...
Enrolling more than one control for each case is an effective method
for  increasing the power of research.
However, incorporating more than two controls per instance adds
little  statistical value.
Data  
Collection Decide on the data to be gathered after precisely  
identifying the cases and controls; both groups must 
 have the same data obtained in the same method.
If the search for primary risk variables is not  
conducted objectively, the study may suffer from  
researcher bias, especially because the conclusion  
is already known.
It's crucial to try to hide the outcome from the person 
 collecting risk factor data or interviewing patients,  
even if it's not always practicable.
Contd...
Patients may be asked questions concerning historical issues (such
as  smoking history, food, usage of conventional eye medications, and so on).
For some people, precisely recalling all of this information may be challenging.
Furthermore, patients who get the result (cases) are more likely to
recall  specifics of unfavourable experiences than controls.
Recall bias is a term for this phenomenon.
Any effort made by the researcher to reduce this form of bias would benefit 
 the research.
Analysis
The frequency of each of the measured variables in each  
of the two groups is computed in the analysis.
Case-control studies produce the odds ratio to measure  
the strength of the link between exposure and the  
outcome.
An odds ratio is the ratio of exposure probabilities in the  
case group to the odds of response in the control group.
Calculating a confidence interval for each odds ratio is  
critical.
Contd...
A confidence interval of 1.0 indicates that the link  
between the exposure and the result might have been  
discovered by chance alone and that the link is not  
statistically significant.
Without a confidence interval, an odds ratio isn't  
particularly useful.
Computer programmes are typically used to do these  
computations.
Because no measures are taken in a population-based  
sample, case-control studies cannot give any information  
regarding the incidence or prevalence of a disease.
Risk  
Case-control studies can also be used to investigate risk Factors 
 factors for a rare disease. and  
Cases might be obtained from hospital records. Sampling
Patients who present to the hospital, on the other hand, 
 may not be typical of the general community.
The selection of an appropriate control group
may  provide challenges.
Contd...
Patients from the same hospital who do not have the result are a common source 
 of controls.
However, hospitalized patients may not always reflect the broader population; they 
 are more likely to have health issues and access the healthcare system.
Recent  I) RISK FACTORS RELATED TO 
Research on  MULTIPLE  SCLEROSIS IN KUWAIT
Case-Control This matched case-control research in Kuwait looked 
 Studies  at the relationship between several variables:fhaismtoilyry, stressful events, tobaccosmoke  
using  life  exposure, history, comorbidity, and
Statistical  vmauclctiipnlaet isocnlerosis (MS) risk.
Analyses To accomplish the study's goal, a matched case-  
control strategy was used.
Cases were recruited from Ibn Sina Hospital's  
neurology clinics and the Dasman Diabetes Institute's 
 MS clinic.
Contd...
Controls were chosen from among Kuwait University's faculty and students.
A generalized questionnaire was used to collect data on socio-demographic,  
possibly genetic, and environmental aspects from each patient and his/her pair-  
matched control.
Descriptive statistics were produced, including means and standard deviations for  
quantitative variables and frequencies for qualitative variables.
Variables  that  were  substantially  (p  ≤ 0.15)  associated  with  MS  status  in  
the  univariable conditional logistic regression analysis were evaluated for 
inclusion in  the final multivariable conditional logistic regression model.
Contd...
In this case-control study, 112 MS patients were invited to participate, and 110  
(98.2 %) agreed to participate.
Therefore, 110 MS patients and 110 control participants were enlisted, and they  
were individually matched with cases (1:1) on age (5 years), gender, and  
nationality (Fig. 1).
The findings revealed that having a family history of MS was significantly  
associated with an increased risk of developing MS.
In contrast, vaccination against influenza A and B viruses provided significant  
protection against MS.
Contd...
Contd...
II) RELATION BETWEEN PERIODONTITIS AND COVID-19 INFECTION
COVID-19 is linked to a higher inflammatory response, which can be deadly.  
Periodontitis is characterized by systemic inflammation.
In Qatar, patients with COVID-19 were chosen from Hamad Medical  
Corporation's (HMC) national electronic health data.
Patients with COVID-19 problems (death, ICU hospitalizations, or assisted  
ventilation) were categorized as cases, while COVID-19 patients released without 
 severe difficulties were categorized as controls.
Contd...
There was no control matching because all controls were included in the  
analysis.
Periodontal problems were evaluated using dental radiographs from the same  
database.
The relationships between periodontitis and COVID 19 problems were  
investigated using logistic regression models adjusted for demographic, medical,  
and behavioural variables. 258 of the 568 participants had periodontitis.
Only 33 of the 310 patients with periodontitis had COVID-19 issues, whereas only 
 7 of the 310 patients without periodontitis had COVID-19 issues.
Contd...
Table 2 shows the unadjusted and adjusted odds ratios and 95 % confidence  
intervals for the relationship between periodontitis and COVID-19 problems.
Periodontitis was shown to be substantially related to a greater risk of COVID-19  
complications, such as ICU admission, the requirement for assisted breathing,  
and mortality, as well as higher blood levels of indicators connected to a poor  
COVID-19 outcome, such as D-dimer, WBC, and CRP.
III) MENSTRUAL, REPRODUCTIVE AND HORMONAL FACTORS AND 
THYROID  CANCER
The relationships between menstrual, reproductive, and hormonal variables and  
thyroid cancer incidence in a population of Chinese women were investigated in  
this study.
Contd...
A 1:1 corresponding hospital-based Case-control study was conducted in 7  
counties of Zhejiang Province to investigate the correlations of diabetes mellitus  
and other variables with thyroid cancer.
Case participants were eligible if they were diagnosed with primary thyroid cancer  
for the first time in a hospital between July 2015 and December 2017.
The patients and controls in this research were chosen at random.
At enrollment, the interviewer gathered all essential information face-to-face using 
 a customized questionnaire.
Descriptive statistics were utilized to characterize the baseline characteristics of  
female individuals using frequency and percentage.
Contd...
To investigate the connections between the variables  and thyroid cancer,
univariate conditional logistic regression models were used.
We used four multivariable conditional logistic regression models adjusted for  
variables to investigate the relationships between menstrual, reproductive, and  
hormonal variables and thyroid cancer.
In all, 2937 pairs of participants took part in the case-control research.
The findings revealed that a later age at first pregnancy and a longer duration of  
breastfeeding were substantially linked with a lower occurrence of thyroid cancer, 
 which might shed light on the aetiology, monitoring, and prevention of thyroid  
cancer in Chinese women.
Contd...

Conclusion
It's important to note that the term "case-control study" is  
commonly misunderstood.
A case-control study begins with a group of individuals  
who have been exposed to something and a comparative  
group (control group) who have not been exposed to  
anything and follows them over time to observe what  
happens.
However, this is not a case-control study. Case-control  
studies are frequently seen as less valuable since they  
are retrospective.
Contd...
They can, however, be a highly effective technique of  
detecting a link between an exposure and a result.
They are sometimes the only ethical approach to  
research a connection.
Case-control studies can provide useful information if  
definitions, controls, and the possibility for bias are  
carefully considered.
Contact Us
UNITED KINGDOM
+44- 7424810299
INDIA
+91-9884350006
EMAIL
[email protected]