PHC 215 Assignment 1: Critical Appraisal of Breast Cancer Study

This assignment is a critical appraisal of a case-control study investigating the determinants of breast cancer among Saudi women in the Makkah region. The study, titled "Determinants of breast cancer in Saudi women from Makkah region: a case-control study," examines various risk factors, including socioeconomic factors, health-related characteristics, menstrual histories, and breastfeeding practices. The assignment involves using a provided checklist to evaluate the study's methodology, including how the groups were compared, matching of cases and controls, criteria used for identification, exposure measurement, confounding factors, strategies to deal with confounding, outcome assessment, exposure period, and statistical analysis. The student evaluates the study based on the checklist, providing 'Yes,' 'No,' 'Unclear,' or 'Not Applicable' answers to assess the study's strengths and weaknesses, and provides a critical review of the study.

Check List
Yes No Unclear Not
applicable
1. Were the groups comparable other than the presence of
disease in cases or the absence of disease in controls?
✓ □ □
1. Were cases and controls matched appropriately? ✓ □ □ □
1. Were the same criteria used for identification of cases
and controls?
✓ □ □ □
1. Was exposure measured in a standard, valid and reliable
way?
✓ □ □ □
1. Was exposure measured in the same way for cases and
controls?
✓ □ □ □
1. Were confounding factors identified? ✓ □ □ □
1. Were strategies to deal with confounding factors stated? ✓ □ □ □
1. Were outcomes assessed in a standard, valid and reliable
way for cases and controls?
✓ □ □ □
1. Was the exposure period of interest long enough to be
meaningful?
✓ □ □ □
1. Was appropriate statistical analysis used? ✓ □ □ □

Case Control Studies Critical Appraisal Tool
Answers: Yes, No, Unclear or Not/Applicable
1. Were the groups comparable other than presence of disease in cases or absence of
disease in controls?
The control group should be representative of the source population that produced the cases. This
is usually done by individual matching; wherein controls are selected for each case on the basis
of similarity with respect to certain characteristics other than the exposure of interest. Frequency
or group matching is an alternative method. Selection bias may result if the groups are not
comparable.
2. Were cases and controls matched appropriately?
As in item 1, the study should include clear definitions of the source population. Sources from
which cases and controls were recruited should be carefully looked at. For example, cancer
registries may be used to recruit participants in a study examining risk factors for lung cancer,
which typify population-based case control studies. Study participants may be selected from the
target population, the source population, or from a pool of eligible participants (such as in
hospital-based case control studies).
3. Were the same criteria used for identification of cases and controls?
It is useful to determine if patients were included in the study based on either a specified
diagnosis or definition. This is more likely to decrease the risk of bias. Characteristics are
another useful approach to matching groups, and studies that did not use specified diagnostic
methods or definitions should provide evidence on matching by key characteristics. A case
should be defined clearly. It is also important that controls must fulfil all the eligibility criteria
defined for the cases except for those relating to diagnosis of the disease.
4. Was exposure measured in a standard, valid and reliable way?
The study should clearly describe the method of measurement of exposure. Assessing validity
requires that a 'gold standard' is available to which the measure can be compared. The validity of
exposure measurement usually relates to whether a current measure is appropriate or whether a
measure of past exposure is needed.
Case control studies may investigate many different ‘exposures’ that may or may not be
associated with the condition. In these cases, reviewers should use the main exposure of interest
for their review to answer this question when using this tool at the study level.
Reliability refers to the processes included in an epidemiological study to check repeatability of
measurements of the exposures. These usually include intra-observer reliability and inter-
observer reliability.
5. Was exposure measured in the same way for cases and controls?
As in item 4, the study should clearly describe the method of measurement of exposure. The
exposure measures should be clearly defined and described in detail. Assessment of exposure or
risk factors should have been carried out according to same procedures or protocols for both
cases and controls.

6. Were confounding factors identified?
Confounding has occurred where the estimated intervention exposure effect is biased by the
presence of some difference between the comparison groups (apart from the exposure
investigated/of interest). Typical confounders include baseline characteristics, prognostic factors,
or concomitant exposures (e.g. smoking). A confounder is a difference between the comparison
groups and it influences the direction of the study results. A high quality study at the level of
case control design will identify the potential confounders and measure them (where possible).
This is difficult for studies where behavioral, attitudinal or lifestyle factors may impact on the
results.
7. Were strategies to deal with confounding factors stated?
Strategies to deal with effects of confounding factors may be dealt within the study design or in
data analysis. By matching or stratifying sampling of participants, effects of confounding factors
can be adjusted for. When dealing with adjustment in data analysis, assess the statistics used in
the study. Most will be some form of multivariate regression analysis to account for the
confounding factors measured. Look out for a description of statistical methods as regression
methods such as logistic regression are usually employed to deal with confounding factors/
variables of interest.
8. Were outcomes assessed in a standard, valid and reliable way for cases and
controls?
Read the methods section of the paper. If for e.g. lung cancer is assessed based on existing
definitions or diagnostic criteria, then the answer to this question is likely to be yes. If lung
cancer is assessed using observer reported, or self-reported scales, the risk of over- or under-
reporting is increased, and objectivity is compromised. Importantly, determine if the
measurement tools used were validated instruments as this has a significant impact on outcome
assessment validity.
Having established the objectivity of the outcome measurement (e.g. lung cancer) instrument,
it’s important to establish how the measurement was conducted. Were those involved in
collecting data trained or educated in the use of the instrument/s? (e.g. radiographers). If there
was more than one data collector, were they similar in terms of level of education, clinical or
research experience, or level of responsibility in the piece of research being appraised?
9. Was the exposure period of interest long enough to be meaningful?
It is particularly important in a case control study that the exposure time was sufficient enough to
show an association between the exposure and the outcome. It may be that the exposure period
may be too short or too long to influence the outcome.
10. Was appropriate statistical analysis used?
As with any consideration of statistical analysis, consideration should be given to whether there
was a more appropriate alternate statistical method that could have been used. The methods
section should be detailed enough for reviewers to identify which analytical techniques were
used (in particular, regression or stratification) and how specific confounders were measured.

For studies utilizing regression analysis, it is useful to identify if the study identified which
variables were included and how they related to the outcome. If stratification was the analytical
approach used, were the strata of analysis defined by the specified variables? Additionally, it is
also important to assess the appropriateness of the analytical strategy in terms of the assumptions
associated with the approach as differing methods of analysis are based on differing assumptions
about the data and how it will respond.