MODULE 1 - POPHLTH 111

Question 1

What is the main goal of epidemiology?

Answer 1

To measure the occurrence of dis-eases in populations and measure the factors of causes in different populations.

Question 2

What is the key feature of epidemiological study?

Answer 2

It ALWAYS starts with a population.

Question 3

What is the numerator and denominator of epidemiological studies?

Answer 3

Denominator: The TOTAL number of people in a population. Numerator: The number of people who dis-ease occurs.

Question 4

Why epidemiologists often age standardise measures of dis-ease frequency before making comparisons between populations?

Answer 4

Age-standarise is a way to make a fair and equal comparison of dis-ease occurrence between populations. This is because different populations have different age structures, which will affect the outcome of the dis-ease. (E.G older people are more likely to die from a dis-ease than younger people).

Question 5

What does population/ group mean?

Answer 5

Sharing one or more common feature . E.g: Same age, gender or ethnicity.

Question 6

What is the death rate in NZ and what does this mean?

Answer 6

100% or one person per lifetime. This is because everyone dies once in their life. What is important it to understand that without a specific time frame, the measure will not be meaningful. E= (n/d) / t. So instead, you must say what is the death rate in NZ per year?

Question 7

When to use E= n / d and when to use E = (n/d) / t.

Answer 7

1. Use that when looking at the proportion. 2. Looking at the specific time rate.

Question 8

What are the common design features of PECOT on the Gate Frame?

Answer 8

P - Total participant population (Triangle)
E - Exposure groups (Sub- denominator, circle)
C- Comparison groups (Sub- denominator, circle )
O - Outcome (People who got the dis-ease from the exposure group and comparison group, square)
T - Time (Arrow)

Question 9

Difference between EG and EGO

Answer 9

EG is the no. of people who got exposed (sub-denominator) and EGO are the people who got the outcome from the people that got exposed ( a / EG).

Question 10

2 key Features of cohort study

Answer 10

1. Researchers allocate people in CG and EG by MEASURING (observing what they are already doing).
2. Cohort studies follow up OVER TIME.

Question 11

What is the difference between incidence & prevalence?

Answer 11

Incidence is a type of measure that measures the disease events over a period of time whereas prevalence measures the number of people that have the disease at one point in time.

Question 12

What are the equations for incidence and prevalence?

Answer 12

1. Incidence = (a/ EG) over t and (b/EG) over t
2. Prevalence = ( a / EG) over 1 and (b/EG) over 1.

Question 13

When should you measure prevalence and incidence?

Answer 13

To measure incidence, the events must be easily observable (the number of new COVID-19 cases) and to measure prevalence that is hard to observe if the dis-ease has occurred (people who are obese).

Question 14

Why must dis-ease outcomes in incidence measures be categorical (yes/no)?

Answer 14

So we can count how many people do and do not develop the outcome over time — needed for calculating incidence.

Question 15

What are cross-sectional studies?

Answer 15

Studies that measure the outcome and exposure at the SAME time. It can only measure prevalence.

Question 16

In which situation is it difficult to measure prevalence and how to overcome this?

Answer 16

When it is difficult to measure the outcome at that specific point in time (such as are you suffering from an asthma attack right now?). So instead, we count the people who have had it in a previous time period, but not ALL the cases. This shows that the time arrow is BACKWARDS.

Question 17

What does it mean when the time arrow is horizontal vs backwards?

Answer 17

Both mean that is it a measure of prevalence but horizontal arrow occurs when you are measuring dis-ease occurrence right now and backwards means you are measuring dis-ease occurrence in a past period of time.

Question 18

What types of measure must be death rate?

Answer 18

Incidence

Question 19

What is another way to present numerical health data like cholesterol levels in terms of prevalence?

Answer 19

By reporting the average (mean) cholesterol level in the population.

Question 20

Describe in what situations it would be
most appropriate to measure incidence rather than prevalence and vice versa

Answer 20

For incidence, it would be the most easiest to measure incidence when it is easiest to count when the dis-ease occurs.

Question 21

What are RCTs?

Answer 21

Randomised controlled trials (RCTs) are like cohort studies except participants are allocated randomly to EG or CG. This means participants have equal chance of being allocated to EG or CG.

Question 22

How can we measure prevalence in cohort studies?

Answer 22

During the beginning of a cohort study.

Question 23

List strengths and weaknesses of incidence and prevalence.

Answer 23

Strengths of incidence= incidence is determined only by the dis-
ease risk in a population (its a ‘clean’
measure of dis-ease occurrence), incidence measures include events (N),
population (D) and time (T). Weakness = Measure OVER time (time-consuming).

Strengths of prevalence= prevalence is relatively easy to measure
as you ‘stop time’ and count
Weakness of prevalence = prevalence measures include only events
(N) and population (D) – less information than incidence
* prevalence is determined by the
incidence, cure rate and death rate (its a ‘dirty’ measure of dis-ease occurrence).

Question 24

How do you calculate RD and RR?

Answer 24

RD is EGO - CGO. It MUST include units. RR is EGO / CGO. It doesn’t have units.

Question 25

What are ecological RCTs?

Answer 25

Ecological RCTs are a type of study where the participants are geographical regions AND these regions are randomised.

Question 26

When do you use PECOT and PEOT?

Answer 26

1. You use PECOT when comparing 2 groups (Is depression more common in university students who sleep less than 6 hours a night compared to those who sleep more?) and you use PEOT when there is NO comparison being made which sometimes are measures of prevalence in cross-sectional studies. (What percentage of university students currently have depression).

Question 27

What does RD = 0 mean and RR = 1 ?

Answer 27

RD = 0 there is no difference in the risk of the outcome between the exposed group and the comparison group. This is also known as the ‘no-effect value;’ remember that the equivalent no-effect value for a RR = 1.0). RR =1 means the risk is the same in both groups.

Question 28

What does it mean if the Relative Risk (RR) is large but the Risk Difference (RD) is small?

Answer 28

It means the exposure might sound like it has a big effect (e.g. “doubles the risk”), but the actual number of people affected is very small. This makes the finding less meaningful in practical or clinical terms. Always check both RR and RD to understand the true impact!

Question 29

What is RRR and how do we calculate it?

Answer 29

RRR is known as relative risk reduction which indicates that the exposure reduces the risk of the outcome. RRR = (1.0 - RR) x 100. ONLY IF THE RR is less than 1, we minus it from 1 to get RRR.

Question 30

What is RRI?

Answer 30

Relative risk increase (RRI) = (RR - 1) x 100%

Question 31

What is RD and RR?

Answer 31

Two main ways to compare two dis-ease occurrences NOT the measures of dis-ease occurrences.

Question 32

What are non-random errors and how do they occur?

Answer 32

Non-random error occurs because of poor study design, poor study processes or poor study measurement it is called a non-random error (or bias). They are often called biases or systematic errors.

Question 33

What is the R of RANBOMAN?

Answer 33

Are the participants a representative sample from a relevant & defined population? Recruitment error occurs when the participants in a study are not representative of the larger population the study aims to measure, leading to external validity issues.

Question 34

For the R in RANBOMAN, how is it presented?

Answer 34

The triangle  in the GATE frame is divided into 3 overlapping levels, where open top of triangle represents the setting in which the eligible population was recruited, the next one is Eligible Population an identifiable, meaningful population? (Meeting the criteria). The third layer (the one that ends) represents eligible population who actually agree to participate in the study. These are the study participants.

Question 35

Why are non-responders important in recruitment error?

Answer 35

Non-responders are individuals who meet the eligibility criteria for a study but choose not to participate. If non-responders differ from responders in ways that affect the study's outcome (e.g., health status, behaviors), this can introduce bias, known as non-response bias or recruitment error. This is especially important in prevalence studies, as the study findings may not accurately represent the wider population.

Question 36

Describe allocation error. Random allocation error only affects RCTs.

Answer 36

Allocation occurs when were the study participants correctly and successfully allocated to the Exposure Group (EG) and the Comparison Group (CG)? and ii. were the EG and the CG similar at the beginning of the study. There are two types of allocation error: measurement error (cross-sectional & cohort studies) and confounding error which are external factors that can disrupt the outcome of the study (diet, age, stress levels).

Question 37

What is the difference between random allocation and random sampling?

Answer 37

Random allocation refers to the idea of allocating people to EG and CG randomly whilst random sampling is choosing participants from a larger population. Only random allocation is involved in RCTs, NOT random sampling.

Question 38

Where is confounding error found and when is it not found?

Answer 38

Confounding will be present in almost every observational study (cross-sectional, cohort). The best way to reduce the likelihood of confounding is to conduct an RCT. However, confounding can still occur in a large RCT if the random allocation process is not done properly.

Question 39

What is the maintenance of RAMBOMAN and what studies do this?

Answer 39

Were most of the participants maintained throughout the study in the groups (EG & CG) to which they were initially allocated? No loss to follow-up in x-sectional studies because participants not followed up. The best way to keep the degree of maintenance error similar EG and CG is to keep the participants and study practitioners ‘blind’ to whether the participant is receiving the study exposure (E) or the comparison exposure (C). Cohort studies have also of maintenance error. Its not just about it being hard to follow people over time but also whether people stay in their exposure group or not, people not following thier assinged exposure, or people are doing what the other group are doing.

Question 40

What is random error and non-random error? Why are similar studies produce different results ?

Answer 40

Random error are error due to chance and non-random errors are errors due to the study design being poor. These differences in results from similar studies are also random errors

Question 41

Why is it hard to measure the exact reason for dis-ease occurrence in biology?

Answer 41

1. People are moving targets so identical measurements of exposures and outcomes change over time. (Random measurement error) 2. We only measure a sample of the people we want to study, NOT the entire population.

Question 42

Why is it that smaller the random sample, the greater the random sampling error?

Answer 42

The smaller the sample, the less likely it is to be representative of the whole population — just due to random chance.

Question 43

Define 95% confidence interval.

Answer 43

The actual definition of a 95% confidence interval is ‘in 100 identical studies using samples from the same population, 95 out of 100 of the 95% confidence intervals will include the true value in the population that the studies were sampled from’

Question 44

Why type of epidemiological measure has random error?

Answer 44

Every epidemiological measure (EGO, CGO, RR, RD, NNT) has random error which can be estimated by a confidence interval.

Question 45

What does a wider CI and narrow CI tell us?

Answer 45

Wider CI tells us there is more uncertainty in the data and narrower means less uncertainty in the data.

Question 46

What does not statistically significant mean?

Answer 46

It means that there's no strong evidence that the exposure (like a treatment or behaviour) caused a change in the outcome. For example, there is NO strong evidence that a drug worked better than the placebo.

Question 47

What does it mean when 95% CI overlaps RD = 0 and RR=1.

Answer 47

If 95% CIs for the RD (EGO – CGO) overlaps 0, or 95% CI overlaps with RR=1, then there is probably no statistically significant difference between EGO and CGO. In simple terms, there is no strong evidence that the exposure changed the outcome.

Question 48

When does it mean when the CI is statically different between EGO and CGO?

Answer 48

When the 95% CIs for EGO & CGO do not overlap OR the 95% CI for the Risk Difference does not overlap the no effect line (RD=0) .

Question 49

How do we reduce random sampling error and random measurement error?

Answer 49

1. Do a bigger study random sample error. 2. Combining studies in a meta-analysis is the next best thing to doing a larger study & reduces random error. Another thing is to do multiple measurements.

Question 50

When do we use the different types of study?

Answer 50

1. It is ethical, affordable and practical? 2. Depends on the question.

Question 51

Finally, at the end of the 6-month follow-up period, participants would receive another Covid-19 test. Why wouldn't there be outcome measurement error?

Answer 51

Covid-19 test is an objective and more accurate, so there would not be any error.

Question 52

What is the main way to reduce maintenance error?

Answer 52

Blinding both participants and researchers. Blinding also reduces BOM as well.

Question 53

How to calculate age specific death rate ?

Answer 53

no of deaths in that age group / no of people in that age population .

Question 54

How to calculate age standardise ?

Answer 54

First calculate age specific death rate. Then expected deaths rate = standard times age specific population. Add all the expected death rates / total standard population .