Cert. 26H Module 3

Epidemiology Lectures 12-17 (so far)

How does the World Health Organization describe Epidemiology?

“Epidemiology is the statistical study of the distribution and the determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health-related problems”

What does Epidemiology essentially do?

The study of the occurrence of dis-ease in populations

• Epidemiology compares the amount of dis-ease that occurs in different populations, and tries to determine why the occurrences between the two (or more) populations differ.

• Essentially: Why is A different to B → Therefore epidemiological studies are conducted to identify and analyse these differences

What is the epidemiology equation?

Numerator / Denominator / Time or N / D / T

• Numerator: whatever area of the outcome you are looking at

• Denominator: total no. of participants within the EG or CG (depends on whatever group you were looking at for the numerator)

What is GATE

• Graphic Approach To Epidemiology

• The map of all epidemiological studies (it is a tool to understand them)

• The underlying principles of all epidemiological studies

• Consist of: a triangle, circle, square, and x

What is PECOT?

Describes all the parts of an Epidemiological study

• Population/Participants (triangle in GATE frame)

• Exposure + Comparison (circle in GATE frame)

• Outcome/s (square in GATE frame)

• Time (x in GATE frame)

Describe occurrence (with regards to health)

Transition from a non dis-eased state to a dis-eased state

Means that a health outcome or a risk factor has occurred

Explain Measure of Occurences

It is: the fact or frequency of something happening / something that occurs and how frequent it occurs

expressed by the epidemiological equation: N / D / T

What is incidence?

refers to the number of health-related events that occur over a period of time.

“refers to the occurrence of new cases of disease or injury in a population over a specified period of time” (Centre for Disease Control, 2012)

What is prevalence?

refers to the number of people with a defined health status at one point in time

“is the proportion of persons in a population who have a particular disease or attribute at a specified point in time or over a specific period of time” (Centre for Disease Control, 2012)

Compare + Contrast Incidence and Prevalence

Both are types of measures of occurrence.

Incidence measures the number of health-related events that occur over a period of time, while prevalence refers to the number of people with a defined health status at one point in time

Describe dis-ease

Dis-ease encompasses all health-related events and health-related states

Why we say dis-ease: to encompass diseases + anything that is away from being healthy/calming/at ease.

What are research methods?

Systematic approaches to gathering information

What is an inductive approach?

Start with observations and then develop your theory (based on the observations)

What is a deductive approach?

start/go in with a theory, test it, refine theory (make observations based off that idea)

How do we differentiate between inductive and deductive?

An inductive approach starts with observations and develops a theory (based on the observations). While a deductive approach starts/goes in with a theory, tests it, and refines the original theory (makes observations based on that idea)

quantitative study meaning

relies on numerical or measurable data

when we quantify something → count the numbers to measure/understand the impacts (see participants as numbers)

qualitative study meaning

relies on personal accounts or documents that illustrate how people think or respond

not necessarily counting people, but how they are feeling → responses and impacts on individuals (e.g. interviews, questionnaires)

How do we differentiate between quantitative and qualitative?

Quantitative counts the numbers to measure/understand the impacts (see participants as numbers), therefore it relies on numerical data or measurable data. While qualitative focuses on how people are feeling, therefore it relies on personal accounts or documents that illustrate how people think or respond (such as interviews + questionnaires)

experimental design meaning

purposely change or control environment / how we as researchers control the natural environment → researches will split participants into group and give them a challenge (to risk bias and confounding) → intervene with the study

observational design meaning

watch how things occur in their natural environment → split people into groups based on the characteristics that have been observed → do not intervene

How do we differentiate between experimental and observational?

1. How we split participants into groups → in experimental design researchers will split people into groups and give them a placebo/test. In observational design, researchers do not intentionally split participants into groups, they split people based on the characteristics they observe

2. How researchers control the environment → intervention in experimental design. no intervention in observational design

What is a longitudinal study?

Participants are followed over time. Outcomes are measured as they occur (incidence → analogy: raindrops) or at various points in time (analogy: buckets on different days)

What is the distinctive attribute of a cross-sectional study?

exposure and outcomes measured at the same point in time (prevalence)

How do we differentiate between a longitudinal and cross-sectional study?

1. Longitudinal measures incidence (outcomes are measured as they occur or at various points in time)  while cross-sectional measures prevalence (exposures and outcomes measured at the same time)

2. Longitudinal follows participants over time, while cross-sectional study is taken at one point in time

Describe randomised control trials (RCTs)

• Form of ‘intervention’ study

• Experimental → we control the environment

• Population allocated into groups → randomly (not based on characteristics) allocate participants into exposure or control groups

• Exposure gets the drug/treatment

• Compare EG outcomes to CG outcomes

• Blind (you do not know what you are taking) or double blind (the researches don’t know either) → to reduce bias, so responses aren’t influenced

Strengths of RCTs?

• Gold standard for treatment

• Good evidence (we look at people over time → longitudinal) that intervention leads to outcome

• Randomisation → because it makes the groups more even / more likely that the groups will be similar

Weaknesses of RCTs?

• Costly → includes recruitment of participants + price of the study itself

• Difficult to follow-up long term

• Ethical limitations

• Can be too small → not a good representative example

• Participants may leave over time (poor retention)

Example of an RCT

Clinical trials for new treatments/medication

Describe cross-sectional studies

• Observational → things are happening in their natural environment or have happened and we are reporting on it

• Measure the prevalence of dis-ease in a population

• Investigating association between risks and dis-ease outcomes → a cross sectional study cannot determine causality

• Taken at one point in time → a snapshot

• Can be repeated over time

Strengths of cross-sectional studies?

• Inexpensive

• easier/faster to conduct

• Capture multiple exposures and outcomes at once

• Easy have a representative sample of the population

Weaknesses of cross-sectional studies?

• Uncertain time sequence (cannot determine causality)

• Confounding common

Example of a cross-sectional study

NZ Health Survey

What is confounding?

the idea that there are other factors in the study/environment affecting the outcomes, therefore affecting the research data

Why is confounding common in observational studies?

because we cannot control the environment

Describe cohort studies

• Longitudinal

• Observational

• Participants are followed up and dis-ease outcomes are measured over time

2 types

• Prospective → follows group/s over time

• Retrospective → looks backwards

Strengths of cohort studies?

• Clear time sequence

• Captures multiple exposures and outcomes

• Less recall bias

Weaknesses of cohort studies?

• Costly

• Not suitable for rare outcomes → difficult to find a representative group for rare outcomes

• Poor follow up and retention 

• Potential confounding

Example of a Cohort study

Growing Up in NZ Study

Describe ecological studies

• Compares groups of populations (meaning they do not look at participants individually)

• Longitudinal or cross-sectional

• Experimental or observational

• Looking at trends and causes of dis-ease

• Determine findings that apply to groups (not individuals)

Strengths of ecological studies?

• Cheaper + Quicker (using data that has already been collected)

• Efficient for rare outcomes

Weaknesses of ecological studies?

• Confounding is common

Example of an Ecological study

Reports comparing rates of dis-eases among different countries

E.g. comparing annual death rate from heart disease in a group of low income countries and in a group of high income countries

What is a non-random error?

error that was caused by a particular way the study was carried out → results in bias when you interpret your final outcome/s

How do we prevent having non-random errors?

using RAMboMAN

What does RAMboMAN stand for?

R for Recruitment

A for Allocation or Adjustment

M for Maintenance

B for Blind

O for Objective

M for Measurement

AN for Analysis

What does Recruitment involve?

• Am I recruiting the right people?

• Are the participants that I have recruited representative of the population I want to analyse?

• Think about response rate. → How many people are responding? Is the response rate high or low?

  engagement levels of the participants prior to the study can affect how they act during the study, which matters because it affects who your participants are
  

Where is Recruitment applied in the GATE frame?

population/participants (triangle)

What does Allocation involve?

• Allocate participants into exposure group or comparison group

• Ideally the two groups should be similar → are the people in my exposure group similar or different to the people in my comparison group?

Why are cohort studies prone to allocation errors?

because the exposure and comparison groups are usually not the same

Where is Allocation applied in the GATE frame?

Exposure/Comparison Groups (circle) → looks at how the participants are being assigned

What does Maintenance involve?

• Have the people who were assigned into a specific group stayed within that group over the study period?

• How likely are they going to maintain that?

Why are there no maintenance errors in cross-sectional studies

This is because the study takes place at one point in time (and the exposure and outcome are measured at the same time), meaning that there is no loss of follow-up or maintaining issues such as poor retention

Where is Maintenance applied in the GATE frame?

between EG/CG and outcomes → maintenance ensures that what is in the EG/CG stays in the EG/CG

What does Blind involve?

one way to measure the outcome/s (relates to Measurement)

blind is when the participants do not know what they are taking / the exposure

double-blind is when both participants and researchers don’t know what people are taking / who has the exposure

• reduce bias

• ensure the validity of results

Where is Blind applied in the GATE frame?

outcomes (square)

What does Objective involve?

one way to measure the outcome/s (relates to Measurement)

• Are the questions you are asking / the findings you are researching objective or subjective?

• Are the findings open to interpretation? If they are = subjective

• Are the findings fixed measures? If they are = objective

Where is Objective applied in the GATE frame?

outcomes (square)

What does Measurement involve?

• How the outcomes were measured (involves blind + objective aspects of RAMboMAn)

• Were they accurate?

• Were they easy to follow up?

Where is Measurement applied in the GATE frame?

outcomes (square)

True/False: Cross-sectional studies measure both exposures and outcomes at the same time

True

True/False: Non-random error looks at how the study is designed

True

True/False: Participants are randomly selected into the study to reduce confounding

False

(I don’t bloody know the answer why → Dennis said he would go over it later)

True/False: Maintenance is one of the common non-random errors for longitudinal studies

True

What is the difference between random recruitment/selection and random allocation?

Random Recruitment/Selection is a random process to recruiting. This is to remove a certain bias + get a representative sample of the population

Random Allocation is the allocation of participants randomly into groups once they are in your study. This ensures that the EG and CG are similar.

How does epidemiology play a role in preventing dis-ease?

• unravels the causal pathway

• directs the preventative action

• evaluates the effectiveness of implemented preventative actions

What are the (3) Population Health Actions?

• Health Promotion

• Disease Prevention

• Health Protection

Describe disease prevention

• Disease focused

• Looks at particular diseases (or injuries) and ways of preventing them  - (e.g. the incidence, the prevalence, risk factors or impacts)

• Aim is to decrease the risks associated with dis-ease → preventing you from getting sick + preventing you from getting more sick one you are diagnosed

What are the two types of disease prevention?

• Population based (mass) strategy

• High risk (individual) strategy

Describe a population based (mass) strategy?

• Focuses on the whole population

• Aims to reduce the health risks/improve the outcome of all individuals in the population

• Useful for a common disease or widespread cause

What are some examples of a population based (mass) strategy?

immunisation programmes, mandatory use of seatbelts, low salt food at supermarkets

Describe a high risk (individual) strategy

• Focuses on individuals perceived to be a high risk

• The intervention is well matched to individuals and their concerns

What are some examples of a high risk (individual) strategy?

intervention targeting obese adults, free needles for intravenous drug users

Describe primary disease prevention

Limit the occurrence of disease by controlling specific causes/exposures and risk factors

Primary disease prevention → targeting exposures → lowering risk of getting disease

Describe secondary disease prevention

Reduce the more serious consequences of disease (by Early identification + intervention )

Describe tertiary disease prevention

Reduce the progress of complications of established disease

What is the fundamental difference between Primary and Secondary Prevention?

Primary → no disease present → preventing you from getting the disease in the first place

Secondary → disease is present → dealing with it efficiently and in timely manner

Describe Health Promotion

• Acts on the determinants of wellbeing

• Health/wellbeing focused

• Enables/empowers people to increase control over, and improve, their health

• Involves whole population in everyday contexts

• Moves away from dis-ease → focusing on social and environmental conditions

What does the Ottawa Charter (1986) acknowledge?

• Health is a fundamental right for everybody

• Achieving good health requires both individual and collective responsibility

• The opportunity to have good health should be equally available

• Good health is an essential element of social and economic development

What are the 3 basic strategies of the Ottawa Charter?

1. Enable (individual level strategy)

2. Advocate (systems level strategy)

3. Mediate (a strategy that joins up individuals, groups and systems)

Describe enable

To provide opportunities for all individuals to make healthy choices through access to information, life skills and supportive environments

Describe advocate

To create favourable political, economic, social, cultural and physical environments by promoting/advocating for health and focusing on achieving equity in health

Describe mediate

To facilitate/ bring together individuals, groups and parties with opposing interests to work together/ come to a compromise for the promotion of health

What are the priority action areas?

• develop interpersonal skills

• strengthen community action

• create supportive environments

• reorient health services towards primary health care

• build healthy public policy

Example/s for ‘develop interpersonal skills’

life skills education in school → empowering people to make the right choices

Example/s for ‘strengthen community action’

self help groups (alcoholic anonymous) + youth health projects → creating health promotion champions in the communities

Example/s for ‘create supportive environments’

building speed bumps, healthy food choices in the school cafeteria

Example/s for ‘reorient health services towards primary health care’

health education services, translator services → essentially making sure the services reflect the needs of the patients

Example/s for ‘build healthy public policy’

taxation on alcohol and cigarettes, mandatory seat belt use, banning of smoking in public places

True/False: Population-based strategies are useful when the disease is prevalent in the community

True

True/False: Health promotion strategies act on the determinants of wellbeing

True

True/False: Secondary prevention strategies limit the prevalence of disease by controlling specific risks

False → this is done by primary prevention

True/False: Tertiary disease prevention focuses on reducing the progress and complication of the of the disease

True

What is the difference between individual and population health care?

• Individual → clinicians generally deal with individuals. They aim to treat dis-ease and restore “health” (treating patients who present)

• Population → population health is concerned with the health of groups of individuals, in the context of their environment (identifying and treating all appropriate patients in a population)

True/False: Epidemiology determines the cause of di-ease in the population

False

Epidemiology determines the relationship or association between a given exposure and dis-ease in populations

What is correlation (or association)?

refers to a statistical relationship between two or more variables → where a change in one variable is associated with a change in another variable. 

What is causation?

refers to a cause-and-effect relationship between two variables → where one variable (the cause) directly influences or leads to another change in another variable (the effect).

What is the difference between correlation/association and causation?

Correlation/Association indicates that there is a connection or pattern between the variables, but it does not imply that one variable causes the other

Causation implies a direct causal connection between the variables.

What is the aim of the Bradford Hill Criteria?

• Helps find the link between exposure and outcome

• Not a checklist but an “aid to thought”

What are the components of the Bradford Hill Criteria?

1. Temporality

2. Strength of association

3. Consistency of association

4. Biological gradient (dose-response)

5. Biological plausibility of association

6. Specificity of association

7. Reversibility

Describe temporality

• First the case then the disease

• Essential to establish a causal relationship