ROD JACKSON THE GOAT

What is epidodemiology?

The study of frequency (/occurrence) of disease in populations

What does the term ‘disease’ mean?

Any health-related event or state - such as death and diabetes

What is an occurrence?

The transition from a non-diseased state to a diseased state

What is a population?

Any group of people who share a common factor

What type of data is dealt with in epidemiological studies?

Quantitative

What are the types of quantitative data?

Categorical or numerical

What is categorical data?

Data grouped into categories e.g. man/woman

What is numerical data?

Data that takes on numerical values e.g. weight and height

What are the visual components of the GATE frame?

Triangle, circle, square, and arrow

What is the GATE frame?

Graph approach to epidemiology

What does the triangle represent in the GATE frame?

The participant population

Divided into 3 parts:

• top = setting

• Middle = eligible population

• Bottom = number of study population

What does the circle represent in the GATE frame?

Study specific sub-denominators = exposure group and comparison group

What does the square represent in the GATE frame?

The numerators (disease outcomes)

What does the arrow represent in the GATE frame?

Time

How do you deal with numerical data in the GATE frame?

They can either be converted to categorical data or average values can be calculated as disease occurrence

What are the two measures of disease occurrence?

Incidence and prevalence

What is incidence?

The measure of onsets of disease occurring during a period of time from the population

What is represented by the vertical arrow?

Incidence - occurrence measured over a specified period of time

What is the equation to calculate incidence?

N/D)/T

N = no. Of ppl in group w disease outcomes

D = no. Of ppl in population

T = time taken for study

Unit is outcomes per number of ppl per time taken for study

What is prevalence?

The measure of the number of people with the disease at a point in time from the population

When is prevalence used?

When the disease is not easily observable e.g. onset of diabetes cannot be easily measured

Also when the outcome can occur many times in a specified period of time e.g. asthma attacks

What does the horizontal arrow represent?

Prevalence - the occurrence was measured at a point in time

What is the equation to calculate prevalence?

N/D

N = No. of ppl who have the disease

D = No. of ppl in population at a point in time

Unit is the outcomes per people in the study at a specified point in time

What is the purpose of epidemiological studies?

To investigate and compare the EGO and CGO and in doing so estimate the association between the outcome and the exposure

What is relative risk RR?

EGO / CGO

either percentage or ratio

What does a RR value of 1 indicate?

EGO = CGO

What is risk difference RD?

EGO - CGO

What is PECOT?

Participants

Exposure group

Comparison group

Outcome

Time

What are the two types of errors?

Random and non-random

What are random errors?

Errors caused due to chance

What are non-random (systematic) errors?

Errors caused by problems with how the study was designed or conducted

What is RAMBOMAN?

Recruitment

Allocation

Maintenance

Blind or Objective Measurements

Analysis

How do systematic errors occur in the recruitment process?

1. When a study on a population is done to approximate and apply the results to a wider population the study population must be recruited from the correct setting to represent the wider population - even in the correct process of sampling random error can occur

2. The participants who meet the eligibility criteria from this setting must all be similar enough to fit into the same population

3. The response rate (proportion of people in the eligible population who choose to take part in the study population) must be high enough so that there is no difference between those who accept to take part in the study and reject to take part in the study

How do systematic errors occur in the allocation process?

1. Measurement error - EGO and CGO measured incorrectly meaning some participants will be allocated to the wrong group

2. Confounding - when there are differences in the EG and CG other than the exposure that affect the study outcome (existence of confounders)

What is a randomised controlled trial?

Study in which the EG and CG are allocated randomly

In theory the two groups formed would be very similar minimising confounding

What is baseline comparison?

Checking the EG and CG differences before a study is commenced

What is concealment of allocation?

A solution to confounding in RCTs where the randomising process can be tampered with. Involves prevention of any possible tampering through study design

How can confounding be reduced?

RCTs
Larger sample size
Stratified analysis (analysis based on differences between groups e.g. age-standardisation)

How do systematic errors occur in the maintenance process?

In the ideal study

• maintain exposure status

• not be exposed to other factors affecting outcome

• not drop out of study

Any comprised factors introduce maintenance error.

How do systematic errors occur in the Blind and Objective measurement process?

Any problem in study design when measuring outcomes will lead to systematic error

How is measurement error reduced?

Set outcome to be objective in that they can be measured easily and clearly

Blind the participants or investigators or both to the knowledge of the exposure

What is random sampling error and why does it occur?

Errors (deviations from the truth) that occur due to chance.

Random sampling errors occur because when investigating the effects of an exposure on dis-ease occurrence, everyone in the population cannot be included - hence, a sample is chosen to represent this population and this creates random sampling error.

How is random error reduced?

Increase sample size

Do repeats on measurements related to allocation and outcome

What does a 95% confidence interval represent?

There is a 95% chance the true value of the occurrence from the whole population is included in the range provided.

What does it mean if the confidence interval for EGO and CGO do not overlap?

Reasonable to assume that the difference is significant and true assuming no systematic error was present

What does it mean if the confidence interval for a calculated RR value includes 1?

The difference in the EGO and CGO is statistically insignificant

What does it mean if the CI for a calculated RD value includes 0?

Difference is not statistically significant

What is meta-analyses?

The combination of multiple studies to demonstrate whether or not the exposure has had a real effect