Critique of epidemiologic studies (ppt)

Critique of Data Collection
Critique of Data Analysis
Critique of Result Interpretation
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Critique of a Study on the "Determinants of Repeated
Abortion Among Reproductive Age Women Attending
HFs in Northern Ethiopia1
, 2015: A Case Control Study
1
Alemayehu M*,Yebyo M, Araya A., Alemayehu B., Misganaw F. & Gelila K.
By: Tesfahun T., Mezgebu Y., Segni M. & Daniel Y.
Submitted to Prof. Yigzaw Kebede
Ethiopian Field Epidemiology and Laboratory Training Program
Institute of Public health
College of Medicine and Health Science
University of Gondar
January, 2018
Gondar, Ethiopia
Tesfahun T., Mezgebu Y., Segni M. & Daniel Y. Critique of an Epidemiologic Study 1/21

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Outlines
1 Critique of Data Collection
Study context and Objectives
Primary Exposure and Outcome
Study Design, Population, Sampling and sample size
Potential for bias and minimizing Confounding eect
2 Critique of Data Analysis
Methods used to control Confounding bias
Measures Association and Statistical Stability
3 Critique of Result Interpretation
Major results of the study
Inuence of bias, confounding and misclassication
Discussion on Limitation and Main Conclusions
Generalizability of the study
Tesfahun T., Mezgebu Y., Segni M. Daniel Y. Critique of an Epidemiologic Study 2/21

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Objectives
To Assess :
Whether appropriate methods used to select the study
subjects and collect and analyze the data
Whether any errors were committed in the design,
conduct or interpretation of the study ndings
What inuece of errors had on the reported ndings.

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Abstract of the Study

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A. Critique of Data Collection
1 What was the context of the study?
Many women throughout the world, experience repeated
abortion in their lifetimes.
Repeat abortion is an indicator of the larger problem of
unintended pregnancy which is associated with many
problems, including poor health.
However, the magnitude of repeated abortion in Ethiopia is
not known. So, the study was conducted to identify
determinants of repeat abortion (Alemayehu et al. 2015)
The Context has been Well Stated
2 What were the objectives of the study?
The main purpose of the study was to identify determinants of
repeat abortion in Tigray Region, Ethiopia.
Clearly stated

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Data Collection ...
3 What was the primary exposure of interest?
Was it accurately measured?
The primary exposures of interest in this study were :
Awareness of fertility return (Yes/No)
History of previous abortion procedures (Medical/Surgical),
Number of sexual partners in the past 12 months
Age at rst sexual intercourse (below 18 years/18 years
above)
perception of painless abortion procedure (Yes/No)
Abortion disclosure to a third party (Yes/No).
As exposure, awareness of fertility return was not accurately
dened and measured because it is not possible to measure
awareness simply by yes or no question. It was better if the
exposure was measured by some list of question that can
measure the awareness of participants.
Probably, this may lead to exposure misclassication.

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Data Collection ...
4 What was the primary Outcome of interest? Was it
accurately measured?
The primary outcome was an episode of abortion
(single Vs Repeated)
During data collection, clients' response was taken in case of
inconsistency with medical record histories.
Probably, this may lead to inaccurate measurement which can
result in misclassication.
Because, if there is a history of abortion in the medical record
of a women, there is no enough evidence to reject it and
clients may deny it due to sensitiveness of the issue.

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Data Collection ...
5 What type of study was conducted?
A case control study (Unmatched) was conducted.
It is appropriate, But if possible Matched Case control is
better
6 Describe the source population, process of subject
selection, sample size, and ratio of cases to controls.
The source population in this study was women who received
abortion care services in the health Facilities of Tigray region.
The ratio of case to control subjects was one to two
A total 315 of Sample size was planned and 309 were studied
(98% response rate).
Cases were selected by non-probability and controls by
randomization (Systematic random sampling)

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Data Collection ...
7 Could there have been bias in the selection of the
study subjects? How likely was this bias?
Selection bias is more likely because dierent methods are
used to select cases and controls.
Cases were selected non-randomly while controls randomly.
Even there may be referral of subjects according to an
exposure or diseases status so that selection bias occurred.
8 Could there have been bias in the collection of
information? How likely was this bias?
The history abortion is not easily forgettable and it was
veried by medical record review so that recall bias is unlikely.
However,information bias probably resulted from sensitiveness
of the issue so that the study participants are more likely to
provide a socially acceptable response (Social desirability bias)
In addition, the data collectors were not blinded and
interviewer bias is likely.

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Data Collection ...
9 What were made to minimize the confounding eect
prior to data analysis? Were these provisions
sucient?
Randomization for selecting the government hospitals and
controls were used.
The same source population for the cases and controls were
used
However, these provisions might not be sucient to minimize
the inuence of confounding factors prior to data analysis.
It would be better if :
The cases were selected randomly.
The cases and controls were matched.
Multistage Stratied sampling was used.

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B. Critique of data analysis
1 What methods were used to control confounding bias
during data analysis? Were these methods sucient?
Multivariable logistic regression analyses were used.
This allows investigators to control for many
confounders simultaneously.
However, it might not be sucient to control confounding bias.
Stratied analysis might be better for the evaluation of the
association within homogeneous categories (strata) of the
confounding variable.
The narrower the category is, the better the control
of confounding.

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Data Analysis ...
2 What measures of association were reported in this
study?
The study reported odd ratios.
3 What measures of statistical stability were reported
in this study?
The study reported 95% condence intervals p-values

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C. Critique of Result Interpretation
1 What were the major results of this study?
Among the total 309 women who visited the abortion care
service, 105(33.9%) were cases (repeated abortions) and 204
(66.1%) controls (single abortions) with the mean age of 24
years (SD+6.9) and 22 years (SD+6.3) respectively.
The study found that unaware of fertility return[OR=2.0, 95%
CI (1.12, 3.69)], Previous history of medical abortion [OR=3.3,
95% CI( 1.83,6.11)], multiple sexual partners [OR=4.4, 95%
CI (2.39,8.45)], perception of painless abortion procedure
[OR=2.3, 95%CI (1.31, 4.26)], initiating sexual intercourse
before the age of 18 years [OR=2.7, 95%CI (1.49,5.23)] and
abortion disclosure to a third party [OR=2.1, 95%CI
(1.23,3.83) were independent predictors of repeated abortion.

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Result Interpretation ...
2 How was the interpretation of results aected by bias
and confounding? Discuss the direction and
magnitude of bias
The result mainly inuenced by both selection and
information (particularly social desirability bias) biases.
Because the cases were selected by non-random technique and
clients are more likely more likely to provide a socially
acceptable response.
Hence, the association is more likely to be underestimated
(towards the null).

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3 How is the interpretation of the results aected by
non-dierential misclassication? Discuss the
direction and magnitude of this misclassication.
In the abortion episode measurement, client's response
was taken in case of inconsistency with medical records.
In the awareness of fertility return measurement, only
Yes or No questions were used which may not be
appropriate to measure awareness.
Such non-dierential misclassication of a binary exposure
(Awarness) and outcome of interest(Abortion episode) is
predictable in direction,probably toward the null value
(Gullen et al. 1968 ; Copeland et al. 1977)

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4 Did the discussion section adequately address the
limitations of the Study?
The discussion session addresses the limitations of the study
and states the following limitations :
Selecting cases consecutively may not give equal chance for
the women to be enrolled in our study
Inability to identify previous abortion in other health facilities

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5 What were the authors' main conclusions? Were they
justied by the ndings?
The authors conclude that unaware of fertility return, previous
medical abortion history, multiple sexual partners, age below
18 years at rst sexual intercourse, perception of painless
abortion procedure, abortion disclosure to a third party were
associated factors for repeated abortions in Tigray, Ethiopia.
These conclusions are justied by other ndings

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6 To what larger population can the results be
generalized?
The study was prone to selection and information bias which
reduces the internal validity of the study
.
The study subjects were selected only from government
hospitals which could not represent the entire population of
Tigray Region because of dierence in settings of government
hospitals, private hospitals and health centers. Even there may
be dierence in urban and rural health facilities (poor
external validity)
So,it would be unwise to generalize these results to the general
population in Tigray region.
Probably, generalizable to those who received abortion care at
gov't hospitals in Tigray region ( ? ? ?)

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Aknowledegement
Prof Yigzaw Kebede
Alemayehu S. (Assistant prof)
Fentahun Ayenew (MPH)

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Reference
[1] Alemayehu et al, 2015 Determinants of repeated abortion among
women of reproductive age attending health facilities in Northern
Ethiopia : a case control study BMC Public Health (2017) , 17 :188,
DOI : 10.1186/s12889-017-4106-1
[2] Ann Aschengrau, George R. Seage III Essentials of Epidemiology in
Public Health, 3rd edition. Jones and Bartlet Publishers, 2013.

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Thank You !

Critique of epidemiologic studies (ppt)

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