Epidemiology and research

Question 1

Definition:

Livebirth

Answer 1

the complete expulsion or extraction from its mother of a product of conception, irrespective of the duration of the pregnancy, which, after such separation, breathes or shows any other evidence of life such as heartbeat, umbilical cord pulsation, or definite movement of voluntary muscles, whether the umbilical cord has been cut or the placenta is attached

(WHO)

Question 2

Definition miscarriage

Answer 2

Pregnancy loss before 20 weeks

Question 3

Definition still birth

Answer 3

Pregnancy loss after 20 weeks or <400g with no signs of life at birth

Question 4

Definition Preterm birth

Answer 4

Birth before 37 weeks

Question 5

Definition neonatal mortality

Answer 5

Death of a live born baby within 28 days

Question 6

Definition perinatal mortality

Answer 6

Still birth or death within the first week of life (NZ)

Or within 28 days of birth (Aus)

Question 7

Definition infant mortality

Answer 7

Death of a child under the age of 1 year.

The rate is classified as number of deaths per 1000 live births.

Question 8

Definition maternal morbidity

Answer 8

any short- or long-term health problems that result from being pregnant and giving birth

OR

any health condition attributed to and/or aggravated by pregnancy and childbirth that has a negative impact on the woman’s wellbeing

Question 9

Definition maternal mortality

Answer 9

Maternal death is the death of a woman while pregnant or within 42 days of termination of pregnancy (miscarriage, termination or birth), irrespective of the duration and site of the pregnancy, from any cause related to or aggravated by the pregnancy or its management, but not from accidental or incidental causes

Maternal mortality rate (MMR) is the number of maternal deaths per 100,000 women giving birth.

Question 10

Definition low birth weight and very low birth weight.

Answer 10

Weight at birth <2500g, and <1500g respectively.

Question 11

Major causes of perinatal morbidity and mortality?

Answer 11

Prematurity 
Fetal growth restriction/low birthweight
Congenital anomalies
Infection 
Birth asphyxia/hypoxia

Question 12

Definition of:

Quantitative variables (discrete and continuous)

Answer 12

Data in the form of counts or numbers, so that each data set has a unique numerical value.

Discrete variable is a type of quantitative variable that only take a finite number of defined numerical values, usually integers.

Continuous variable refers to the numerical variable whose value is attained by measuring an outcome and can assume any numerical value along a continuum.

Question 13

Definition of:

Qualitative variables (categorical)

Answer 13

A variable that fits into a specific defined category with a set number of variable outcomes, on the basis of some qualitative property.
Theses can be nominal (named) - e.g. marital status or ethnicity. Or ordinal (where the categories are ordered so as to describe progression) - e.g. cancer stage I, II, II, IV.

Question 14

Definition of:

mean

Answer 14

The sum of the values of all observations or data points divided by the number of observations

Question 15

Definition of:

median

Answer 15

the value separating the higher half from the lower half of a data sample

Question 16

Definition of:

mode

Answer 16

the most commonly observed value in a set of data

Question 17

Definition of:

Symmetric (parametric) and asymmetric (non-parametric) frequency distributions

Answer 17

Parametric- sample follows normal distribution.
Example of tests: paired t-test, unpaired t-test, pearson correlation

Non-parametric: no assumptions made about sample.
Example: Wilcoxon rank-sum, Mann-Whitney U test, Spearman, Kruksal wallis

Question 18

Definition of:

Measures of dispersion or variability: range and standard deviation

Answer 18

Range: The difference between the lowest and highest values

Standard deviation: a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean (also called the expected value) of the set, while a high standard deviation indicates that the values are spread out over a wider range.

Question 19

Definition of:

Standard error and confidence intervals

Answer 19

Standard error: a measure of how far the sample mean is likely to differ from the population mean.

Confidence intervals: a range of values for which a population parameter will fall between at a certain level of confidence (e.g. 95% CI). Confidence intervals measure the degree of uncertainty or certainty in a sampling method.

Question 20

Different statistical tests used for data analysis:

• Continuous data (parametric and non-parametric)
• Categorical data

Answer 20

Continuous data: parametric unpaired (T-test) and paired (paired T-test)
non-parametric unpaired (Mann-Whitney) and paired (Wilcoxen)

Categorical data: unpaired (Chi-square) and paired (McNemar’s)

Question 21

Definition of:

Prevalence

Answer 21

The proportion of a population affected by a medical condition at a given point in time.

Question 22

Definition of:

Relative risk

Answer 22

Relative risk is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group.

Question 23

Definition of:

Numbers needed to treat

Answer 23

This is the number of people who need to take the treatment for one person to benefit from the treatment

Calculation: 1/absolute risk reduction (ARR)

If ARR not known- can be calculated by: Control event rate (CER) - Experimental event rate

Question 24

Definition of:

Incidence

Answer 24

Incidence refers to the occurrence of new cases of disease or injury in a population over a specified period of time

Question 25

Definition of:

cumulative incidence (attack rate)

Answer 25

Calculated as the number of new events or cases of disease divided by the total number of individuals in the population at risk for a specific time interval.
It estimates the risk that an individual will experience an event / develop a disease during a specified period of time.

Question 26

Definition of absolute risk

Answer 26

Probability or risk of an event occuring.

Question 27

Define the term ‘sensitivity’

Answer 27

The true positive rate, or the proportion of people with disease who will test positive.

Question 28

How do you calculate ‘sensitivity’?

Answer 28

Sensitivity = true positive rate / whole population with disease
OR 
A / (A + C).
A = true positives.
C = false negatives

Question 29

Define the term ‘specificity’

Answer 29

The true negative rate, or the proportion of people without disease who will test negative.

Question 30

How do you calculate ‘specificity’?

Answer 30

Specificity = true negative rate / disease absent population 
OR 
D / (B + D).
B = false positives.
D = true negatives.

Question 31

What is positive predictive value?

Answer 31

The proportion of positive results in a test that are true positive results.

PPV = true pos / ( true pos + false pos )

Question 32

How do you calculate positive predictive value?

Answer 32

PPV = A / (A+B).
A = true positives
B = false positives

Question 33

What is negative predictive value?

Answer 33

The proportion of negative results in a test that are true negative results.

Question 34

Is positive and negative predictive values dependent on disease prevalence?

Answer 34

Yes.

Question 35

How do you calculate negative predictive value?

Answer 35

NPV = D / (C + D).
D = true negatives.
C = false negatives.

Question 36

Re maternal mortality: Define the terms ‘direct’, ‘indirect’ and ‘incidental’ causes

Answer 36

○ Direct: relating to the pregnancy or birth
○ Indirect: relating to a pre-existing medical condition or newly diagnosed condition, that is exacerbated by pregnancy or birth.
○ Incidental: unrelated to the pregnancy or birth

Question 37

What is a descriptive study and give 3 examples.

Answer 37

These serve to record activities, observations or events. It is rare for descriptive studies to provide the information necessary to evaluate new treatments, but they can provoke further research and stimulate discussion.

Descriptive studies might take the form of Case Reports, Case Studies or Population Studies. Population Studies are most commonly Cross-sectional Studies.

Question 38

What is an explanatory study and give 3 examples.

Answer 38

Explanatory studies are trying to answer a specific question. They usually seek to find information about the causes of illness, or the effectiveness of treatments.

These can be divided into observational studies, where the researcher identifies a group with a particular disease or exposure:

• case-control
• cohort

Or Interventional, where a specific intervention is enacted and then observed for outcomes:
- RCT

Question 39

Outline and explain the 5 levels of evidence as per RANZCOG.

Answer 39

I - Evidence gained from at least one well designed and conducted RCT.
II - 1 - Evidence gained from well designed and conducted controlled trials, though patients were not randomly allocated to treatment/control groups.
II - 2 - Evidence gained from case-control and cohort observational type studies, whereby causation is much harder to prove.
II - 3 - Evidence gained from other less robust forms of study including case series.
III - Evidence gained from descriptive studies like case reports or based on expert opinion. This is the weakest form of evidence.

Question 40

Outline and explain the 4 levels of evidence used by RCOG and the UK.

Answer 40

A - The evidence is based on consistent findings in randomised controlled trials, cohort studies, and appear valid in different populations.
B - Sometimes these are extrapolations from level A studies, but more usually are the results of retrospective cohort studies or case-control studies.
C - The studies that contribute level C evidence are case series, or sometimes extrapolations made from level B evidence.
D - This, again, is ‘expert opinion’ perhaps based on the results of basic science studies.

Question 41

When do you use the Chi-square test? And the Fishers Exact Test?

Answer 41

Chi-square is used to assess categorical data, where 2 independent groups are compared. It tests if you can reject the null hypothesis (N0) - that there is no association between variables, and accept alternative hypothesis (Na) - that there is an association between variables that is beyond the realms of chance. It requires a contingency table to be calculated.

The fishers exact test is used when on of the cell values in the contingency tables is <5.

Question 42

When is the McNemar test used?

Answer 42

Used for paired categorical data. When testing for significance within the same population, before and after an exposure. These are ‘paired results’.

Question 43

Define cohort study.
Advantages?
Disadvantages?

Answer 43

A cohort, or group of people with a defined set of characteristics (usually a common exposure or risk factor), are identified and followed up over time until an outcome or condition occurs.

Advantages?

• Good for studying effects of a rare exposure
• Can study many outcomes at once
• Can identify late outcomes/complications

Disadvantages?

• Often requires long period of follow-up which is time consuming and costly, with high loss to follow-up
• Needs a large sample size

Question 44

Define RCT.
Advantages?
Disadvantages?

Answer 44

A study design that randomly assigns participants into an experimental/intervention group or a control group. As the study is conducted, the only expected difference between the control and experimental groups in a randomized controlled trial (RCT) is the variable being studied.
Advantages?
- Good randomization will “wash out” any population bias
- Easier to blind/mask than observational studies
- Results can be analyzed with well known statistical tools
- Populations of participating individuals are clearly identified

Disadvantages?

• Careful ethical decision for some interventions if ethical to randomise
• Can be expensive and challenging to run adequately powered RCT

Question 45

Define meta-analysis.
Advantages?
Disadvantages?

Answer 45

A subset of systematic reviews; a method for systematically combining pertinent qualitative and quantitative study data from several selected studies to develop a single conclusion that has greater statistical power. This conclusion is statistically stronger than the analysis of any single study, due to increased numbers of subjects, greater diversity among subjects, or accumulated effects and results.

Advantages

• Greater statistical power
• Confirmatory data analysis
• Greater ability to extrapolate to general population affected
• Considered an evidence-based resource

Disadvantages

• Difficult and time consuming to identify appropriate studies
• Not all studies provide adequate data for inclusion and analysis
• Requires advanced statistical techniques
• Heterogeneity of study populations

Question 46

Describe case-control study.
Advantages?
Disadvantages?

Answer 46

A study that compares patients who have a disease or outcome of interest (cases) with patients who do not have the disease or outcome (controls), and looks back retrospectively to compare how frequently the exposure to a risk factor is present in each group to determine the relationship between the risk factor and the disease.

Advantages

• Good for studying rare conditions or diseases
• Less time needed to conduct the study because the condition or disease has already occurred (retrospective data collection)
• Lets you simultaneously look at multiple risk factors
• Useful as initial studies to establish an association
• Can answer questions that could not be answered through other study designs

Disadvantages

• Retrospective studies have more problems with data quality because they rely on memory and people with a condition will be more motivated to recall risk factors (also called recall bias).
• It can be difficult to find a suitable control group

Question 47

What is selection bias?

Answer 47

When study participants are not selected randomly from a population, and hence may not accurately represent a cross section of a population; i.e. may have other variables in common which can affect the outcome/result. It is a flaw of study design.

Question 48

What is confounding?

Answer 48

When the outcome may not be caused the variable being studied, but rather affected by an associated independent variable.

E.g. Investigating the association between smoking and low birth weight, which is confounded by increased risk of preterm birth, and thus higher chance of low BW.

Question 49

What is recall bias?

Answer 49

A disadvantage of retrospective studies. Participants may not accurately recall events/experiences/outcomes in retrospect. Also participants in whom an outcome/condition occurs are more likely to recall events than those in which the study period was uneventful.

Question 50

Measurement bias/error.

Answer 50

When a non-validated test is used and may result in variable measurements.

E.g. not using a validated health related quality of life questionnaire

Question 51

Sustainable Development Goals (SDG) 3.1 aims to reduce maternal mortality by 2025. What are the targets set out by the Ending Preventable Maternal Mortality (EPMM) initiative to achieve this? (5)

Answer 51

• 90% pregnant women to attend four or more antenatal care visits (towards increasing to eight visits by 2030);
• 90% births to be attended by skilled health personnel;
• 80% women who have just given birth to access postnatal care within two days of delivery;
• 60% of the population to have access to emergency obstetric care within two hours of travel time;
• 65% of women to be able to make informed and empowered decisions regarding sexual relations, contraceptive use, and their reproductive health.

Question 52

Critique MDG 4 - Improving maternal health

Answer 52

• Goal was not met

- However there has been a one third reduction in world wide maternal mortality from 2000 to 2017

Question 53

What is the maternal mortality ratio for Aus/NZ?

Answer 53

aus = 5 per 100,000
NZ = 9 per 100,000 (2017)

Question 54

What are the top 3 causes of maternal mortality in NZ?

Answer 54

1) suicide (>25% all maternal mortality in NZ!!!!)
2) AFE
3) VTE and sepsis joint