Study Outcomes - Risk

Question 1

What is Epidemiology?

Answer 1

Study of disease and how it detracts from human health

Describes why certain groups of people develop particular diseases whereas others to not

Question 2

What is Pharmacoepidemiology?

Answer 2

The study of the use and the effects of medicines in large numbers of people

Question 3

What is Biostatistics?

Answer 3

The study of measurement of biological or health data

Question 4

What is Proportion?

Answer 4

Number of a population who have disease X

Question 5

What is Rate and Frequency?

Answer 5

Mean the same thing

They refer to the number of people in a population experiencing a certain event over a period of time. In other words, the event rate in a population over time

Question 6

What is Risk?

Answer 6

The likelihood that something specific will occur to an individual

Question 7

What is the Population at Risk?

Answer 7

The population of interest that can develop the disease

If you already have the disease, you’re not considered to be at risk of developing the disease

If you are dead you are not at risk (or part of the population)

Question 8

What is Point Prevalence?

Answer 8

The proportion of people in the population who have the disease at a given time

Question 9

What is Incidence?

Answer 9

The frequency of occurrence of something in a populations (i.e. how many new cases over time)

Question 10

What is Sensitivity?

Answer 10

The probability of a positive test in a diseased person

Question 11

What is Positive Predictive Value?

Answer 11

The probability that somebody has the disease in question given a positive test result

Question 12

Sensitivity and Specificity is independent of what?

Answer 12

Prevalence

Question 13

Positive Predictive Value and Negative Predictive Value are dependent on?

Answer 13

The underlying risk/prevalence of the disease in the population

Question 14

When Prevalence is Low, what is PPV and NPV?

Answer 14

PPV is low, meaning there is a low chance that someone with a positive actually has the disease (since it is so rare)

NPV is high, meaning there is a high chance a negative is indicative of no disease, again because so few people actually have the disease.

Question 15

When Prevalence is High, what is PPV and NPV?

Answer 15

PPV is high, so a positive is probably indicative of the disease. More people have the disease now, so it is less unlikely for someone to have the disease.

NPV is low, so a negative does not always mean there is no disease. Diseased people can still get negative results.

Question 16

When do False Positives Occur?

Answer 16

Occur when a positive result is taken, but the person does not have the disease. As such, treatment is often begun as we think they have the disease

Question 17

False Positives are an issue when?

Answer 17

The treatment is expensive or harmful

There are no other confirmatory tests available (i.e. everything hinges on this test)

Question 18

When do False Negatives Occur?

Answer 18

Occur when a negative result is taken, but the person actually has the disease. In this case, the patient does not receive treatment when they really need it.

Question 19

False Negatives are an issue when?

Answer 19

The disease is rapidly progressing

The disease is highly harmful

There is a drug that could be used to cure/treat the disease

Question 20

What are Health Related Events?

Answer 20

Any important change or outcome:

Death

Getting acute or chronic disease

Recovery

Progression of a disease

Onset of a symptom

Significant change in clinical sign (e.g. increase in BP by 10mmHg)

Question 21

What are events?

Answer 21

Something to be avoided (e.g. death)

Something to try to achieve (e.g. time to recover from infection)

Question 22

What are Composite events?

Answer 22

Used as an end-point to reduce the number of participants in a clinical trial

Question 23

What is Mortality?

Answer 23

Incidence of death (the event is death)

Can be expressed as: Incidence proportion (most common), Incidence odds/curve/hazard/time

Question 24

What are mortality curves?

Answer 24

Show the risk of death over time

Question 25

What are survival curves?

Answer 25

Express how survival changes over time

Question 26

What is Survival?

Answer 26

The proportion of individuals that are alive (i.e. not dead) after a specific period of time

Question 27

How do you calculate Survival?

Answer 27

1 - mortality incidence proportion

Question 28

What is Odds?

Answer 28

Odds is an alternative to frequency for expressing the frequency of an event over time. It compares the number of people that experience an event to the number that do not

Question 29

If the odds of the event occurring are e.g. 4 to 6, what does this mean?

Answer 29

This means for every 4 people that do experience the event, there are 6 that do not

Question 30

What’s always larger, odds or probability?

Answer 30

Odds are always larger than probability

Question 31

When the disease is rare, what is odds and probability?

Answer 31

odds ~ probability (both are low)

Question 32

When the disease isn’t rare, what is odds and probability?

Answer 32

odds > probability (odds looks way larger)

Question 33

What is Hazard?

Answer 33

The instantaneous risk at a specific moment in time

Question 34

List 3 Common Hazard Function Forms

Answer 34

Bathtub, Decreasing, Constant

Question 35

Common Hazard Function Forms: What is Bathtub?

Answer 35

Initial period of high hazard and hence high mortality, followed by a hazard rate of almost zero, before gradually increasing later in life. Example – normal life.

Question 36

Common Hazard Function Forms: What is Decreasing?

Answer 36

Hazard rate starts high, then decreases over time, resulting in decreased mortality towards the end. Example – most cancers, since many die early, but this starts to decrease as the treatment cures people

Question 37

Common Hazard Function Forms: What is Constant?

Answer 37

Hazard rate does not really change, leading to a constant mortality rate. Example – some cancers that are slow progressing and treated well.