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Test Guided Critical Appraisal: Introduction to Epidemiology Assessment 2 Answer

Unit Learning Outcomes

Upon successfully completing this unit, students should be able to:

1Calculate and interpret measures of morbidity and mortality, and measures of association (including relative and attributable risk)
2Discuss the strengths and weaknesses of the main types of epidemiological study design
3Assess confounding or effect measure modification in epidemiological data
4Assess the likely impact of bias and confounding on measures of association
5Relate concepts of confounding, effect measure modification, and mediation within a putative causal pathway for a given health outcome
6Critically appraise an observed association between an exposure and outcome using a hierarchy of evidence
7Discuss the epidemiologic rationale underlying population and individual disease prevention strategies
8Discuss the inter-relationships between host, agent, and environment in infectious disease epidemiology
9Summarise the requirements of population-based screening and public health surveillance
10Summarise current debates and challenges in epidemiology

Test Guided critical appraisal

Type of Collaboration:Individual
Format:Assignment 2 will have students complete a guided critical appraisal questions related to epidemiological paper chose by the unit coordinator and include a series of
scenario-based calculations and short-answer questions relating to measures of association, confounding and bias.
Length:2,000 words
Curriculum Mode:Short Answer

You will be assessed on the following:

  • Your ability to assess:
  • measures of association between a given exposure and health outcome for different study design
  • ability to identify sources of bias in the paper or a given scenario
  • ability to identify confounders in the paper or a given scenari on and explain their influence on the results
  • ability to identify effect modification in a paper or in a given scenario and explain the results accordingly


Introduction to Epidemiology

Assignment 2

Question 1: 

(a) “What study design does this study employ and identify from the paper methodological features that support the design you just noted ?” 

This particular study is employing the study design of DV(Domestic Violence). Besides this, DV(Domestic Violence) refers to as all sexual, emotional and physical acts by ex- partner or present male sex partner against adult or adolescent females.  In addition to this, pregnancy is defined as a time period when female are more vulnerable to Domestic Violence due to economic, emotional, social and physical changes. According to a national study, it had been found that in the year 2010 the violence against women in Vietnam were increased upto 58 % and all these woman were particularly exposed to Domestic Violence (including sexual violence, emotional violence and physical violence).  The given case study identifies some methodological features which support the study design includes Explorative research method and quantitative method. 

(b) “What is/are the main exposure/s and what is/are the main outcome/s of this study in operational terms (i.e., you answer should include how the measure was defined)?” 

The study design of the sample size was specifically calculated with the help of the sampsi command in the STATA 13.0.  By utilizing sampsi command, a researcher can easily detect the differences in the risks of pre- term birth among Domestic Violence group and group of Non- Domestic Violence (if that certainly exists than power= 0.9) at the level of 0.06.  In addition to this, some criteria was there which was regarded as being exposed to the Domestic Violence includes: 

Sexual violence: without consent and forced sex, have the sexual contact with partner. 

Emotional violence: use/Insult/ Threat weapon to the threat. 

Physical violence:  throw/slap an object/shake/push/twist arm/ punch with and without something which could kick/hurt or try/ and drag to burn or choke. 

Frequency (i.e., n= 1,099) 
Domestic violence 
Sexual + physical 
Sexual + emotional 
Physical+ emotional 
All 3 of them 
Pre- term based outcome 
Low Birthweight 
Low Birthweight/ pre- term 

(c) “Do you think the risk of selection bias is high or low? Your answer should be justified by no more than 60 words!!  Too long answer will be penalised   ?” 

Yes, the risk of selection bias is high because domestic violence has creates lots of problems for the women. Domestic abuse or violence escalates from verbal assault and treat to violence. it can be psychological or physical as well as it can affect any person of any sexual orientation, race, gender and age (Tuan M Vo, 2019).  Domestic violence is violent, intimidating or abusive behaviour in the relationship. 

(d) “Compute the crude OR for domestic violence (yes/no) and pre-term/low birthweight from data presented in Table 4 and interpret this in your own words.” 

No domestic violence is for Pre- term/and low birthweight that is 106(66.3) and 736 (78.4) is for Non- pre – term/ or low birthweight.  Apart from this, yes, domestic violence is for Pre- term/and low birthweight is 54 (33.7) and 203 (21.6). According to POR, no domestic violence is 1 and if the domestic violence is yes than the POR = 1.44*.  In addition to this, 1.04- 1.99= 0.029 that is the P- value.  Besides this, results from certain multivariable analysis proves that the connection and association between low birthweight/ and DV or pre- term remained significant or Domestic Violence exposure was particularly associated with the 1.44 amplified odds that have pre-term or/ and low birthweight contrast to non Domestic Violence exposure (i.e., POR = 1.44 and 95% related CI = 1.99- 1.04). 

(e) “Was the crude OR differ from the adjusted and if yes why? if no why?” 

Yes, the crude is different from the adjusted one because regarding the impact of particular type of Domestic Violence was associated with amplified risk of low and pre- term birthweight, with the POR = 1.49 ( i.e., 95% related CI = 2.19- 1.01). In addition to this, the prevalence or commonness of pre- term based delivery and low birthweight was 14.6%.  apart from this, Domestic Violence may occur after, during and before pregnancy. Because of some changes in female’s economic, social, physical and emotional requirements during the preganancy period, this is the time period when most of the women are vulnerable to Domestic violence. 

 (f) “What was the prevalence of physical violence in this sample and what was the adjusted prevalence odds ratio (POR-Table 5) between physical violence and pre term/low birthweight? Interpret the association in your own words, could it be a result of some error?” 

In Table -5, for physical violence, Non- pre term and low birthweight (i.e., n= 939) is 872(92.9) and 67 (7.1) and pre- term and low birthweight ( i.e, n= 939) is 147(92.9) and 13 (8.1).  Besides this, the adjusted POR (Prevalence Odds Ratio) is 1 for “No” physical violence and 0.69 is for “Yes” physical violence. In the table 5 it has been found that the physical violence is not found more in the case of Non- pre- term and low birthweight delivery. 

(g) “What could be a source of measurement bias in this study and did the authors tried to address this problem. Explain with evidence from the text.” 

Domestic Violence is the major source of the measurement bias which is included in this particular study. Yes, the authors always tried to concentrate on this issue. Apart from Domestic Violence, the authors noted the strong association that has been found between the economic statuses with a pregnancy outcome. They believed that High response rate is one of the biggest strengths of their study. According to the authors, face to face interviews are needed in the medicare because with the help of these interviews, they come to know about the women who are the victim of domestic violence. 

Answers 2: 

(a) “Construct a 2x2 table with columns and rows headings and calculate an appropriate measure of the strength of association between birth defect and folic acid supplements during pregnancy.” 

Birth defect (Yes)
No Birth defect

Yes (Folic acid consumed)
72 + 138 = 210
No (Folic acid consumed)
55+ 70 = 125

N = 72 + 138 +55 +70 = 335

b) “What the name of this measure and how you interpret the findings in (a) in your own words.” 

The strength of association between birth defect and folic acid supplements during pregnancy is the name of this particular measure. In addition to this, the researchers investigated the connection between consuming the supplements of folic acid and birth defect during pregnancy (McStay et al., 2017). 72 infants were there who born with the birth defect or 55 mothers of these infants were there who did take folic acid supplements during their pregnancy. Amongst a control group 70 mothers were there who did not utilize folic acid supplements during pregnancy. 

c) “What proportion of birth defect in the population is potentially preventable, assuming a causal association between folic acid supplement.” explain in words your findings 

23.6% proportion of birth defect is potentially preventable that assume a casual connection among folic acid supplement.  In addition to this, folic acid refers to as the pregnancy superhero. Moreover, consuming the prenatal vitamin with a 400 mcg (micrograms) of the folic acid during and before pregnancy can assist in preventing birth defect of a baby’s spinal cord or brain. Folic acid refers to as a human- made form of vitamin B called folate. Besides this, folate helps in producing red blood cells in baby’s brain or spinal cord (Strøm et al., 2018)

Answer C: 

Use the data in the table to assess the crude association between exposure and disease, and then the association stratified by age” 

In the given case, 51 cases had been exposed to the disease according to the persons years/ 1000(3116).  Moreover, 345 cases were not exposed to the disease according to the persons years/ 1000 (31787). In addition to this, the young adults who were exposed the cases of D is 19 and 1168 is the Persons- years /1000. However, the young adults who are not exposed to the cases of D are 177 as well as 13,177 is the persons – years/1000 (Mayer et al., 2017). Besides this, the old adults who are exposed to the cases of D are 33 according to the persons- years /1000. The old adults who are not exposed to the cases of D are 167 based on the persons- years/1000 (18560).

“After using the statistical software to compute the age-adjusted rate ratio they found that the adjusted RR was 1.51. Is age best characterised as a confounder or an effect measure modifier of the relationship between the rare exposure and disease? Explain.”  

Yes, age is categorised as a confounder because it is a particular confounding factor as well as it is also connected with the certain exposure (which means that the older individuals are likely to be dormant) or it is connected with the certain outcome. Besides this, confounding is the casual concept which cannot be explained in the terms of associations and correlations (Gavurová, Koróny & Šoltés, 2017)

“What is the attributable risk of the exposure in older people?” Chronic obstructive related pulmonary disease is the major attributable risk exposure which is found common in older adults. In addition to this, AR or Attribute risk refers to as a difference among the incidence rate in non- exposed and exposed groups. For example:  attribute risk is calculated with the help of 2×2 table: 

             Contingency and 2×2 Table: 

a+ b
c + d 

        AR= I (E) – I (U)

               = P (D/E)- P (D/U)

               = (A/ (A+B)) – (C/(C+ D))

         AR% = AR* 100

“How would you interpret the finding in 3 (c)?” 

In the context of epidemiology, the access risk or attributable risk refers to as a particular term which is synonymous to the risk difference which has been utilized to denote the attributable fraction between the attributable and exposed fraction for a population (Groenwold et al., 2016). According to 3 (c), Chronic obstructive related pulmonary disease is the major attributable risk exposure which is found common in older adults. 

Questions 4: 

What source of error/bias, if at all, it can introduce to the estimated prevalence? (explain briefly)” 

 The bias was created because of overweight or obese participants(Corsi, Mejía-Guevara & Subramanian,  2016)

What source of error/bias, if at all, in can introduce to the estimated prevalence?  Explain (you can use reference here)

The bias was arise because in another survey to estimate the prevalence of overweight and obesity participants were asked to report on their weight and height from their head. 

“if you were told that women were more likely to underestimate their weight and men accurately report their weight  what source of bias it is :  

Differential misclassification

Differential misclassification occurs when the appropriate information faults differ among groups. However, the bias is certainly different for non- exposed and exposed, or among those who does not have the disease or those who have (Rockett, 2017)

  • Non-differential misclassification

This type of misclassification happens when the certain information is wrong or incorrect. It occurs when the exposure is not related to some other variables and when the certain disease is not related to the other variables. 

  • Recall bias

Recall bias refers to as the systematic error which is caused by the differences in a completeness or accuracy of the certain recollections retrieved by the study participants regarding experiences or events from the certain past (Scott & Maldonado, 2019)

  • Confounding

Confounding is the casual concept which cannot be explained in the terms of associations and correlations.  It observed the relationship between dependent and independent variables (Aleem  et al., 2016). 

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