Session 2

Question 1

What are the types of Variable?

Answer 1

Variables can be divided into discrete (or categorical) and continuous.

Categorical or discrete variables:

Nominal categories into which individuals are classified, these have no numerical relationship e.g. sex (male or female)

ordinal ranking of categories e.g. mild, moderate or severe Interval (categorical) distance between measures on a scale that has meaning e.g. one, two or three people in a household

Continuous variables:

Interval (continuous) distance between measures on a scale has meaning e.g. temperature. However, the ratio between measurements does not have meaning i.e. 10°C is not twice as hot as 5°C.

Ratio the distance and ratio between measurements are defined e.g. weight (1kg is twice the weight of 500g)

Question 2

How can you express continuous vs categorical data?

Answer 2

Histogram: continuous

Bar chart: discrete

Question 3

Define Mode?

Answer 3

Mode the value (or group of values) which occur most often i.e. the highest peak of a histogram.

Question 4

What is the median?

Answer 4

Median the middle value (so arrange in order of size, (n+1)/2th observation if odd or n/2th, if even.

Question 5

Define mean

Answer 5

Mean (average) arithmetic average of observations, mean = (x1 + x2+…+xn)/n

Question 6

what does a symmetrical distribution tell you?

Answer 6

Symmetrical distribution: mean = median

Question 7

What does a skewed distribution tell you?

Answer 7

Skewed distribution:

right: mean > median

left mean < median

Question 8

What is Interquartile range (IQR)?

Answer 8

Interquartile range (IQR) to calculate the IQR, order all the values, Q1 is the value that 25% of observations fall below, Q3 is the value that 75% of observations fall below, IQR = Q3 – Q1

median is the (n + 1) ÷ 2 th value.

Lower quartile is the (n + 1) ÷ 4 th value.

Upper quartile is the 3 (n + 1) ÷ 4 th value.

Question 9

What is standard deviation?

Answer 9

SD: measures the spread in data around the mean

Question 10

What is Variance?

Question 11

What are the methods of presenting and summarizing data?

Question 12

Define incidence

Answer 12

Incidence the number of new cases per population at risk in a given time period

Question 13

Define prevalence

Answer 13

Prevalence the number of all (new + old) cases per population at a given time

Question 14

How do you calculate incidence

Answer 14

Incidence = Number of new cases in a defined population over a given time

Number in defined at-risk population over same

period of time

expressed as a %

Question 15

How do you calculate incidence density and when is it used for?

Answer 15

• if people are followed up for different amounts of time

Number of new cases of a disease

Total person-time at risk of developing a disease

expressed in person-years

Question 16

Why is calculating the incidence useful?

Answer 16

• measure new cases of disease when a disease is of very short duration e.g. massive stroke or even death
• see if new cases of infectious disease are getting more frequent to see if there is an epidemic in progress
• monitor the effect of prevention programmes (i.e. see a fall in frequency of new cases of accidents in accident prevention programme),
• compare people exposed to a potential hazard with those not exposed to help determine if exposure is a real danger to health

Question 17

What is prevalence?

Answer 17

• focuses on health status
• is the proportion of a population in a particular health state

Question 18

How do you calculate Prevalence?

Answer 18

Prevalence = number of cases at a given time

number in the population at that time

Question 19

Why is it important to calculate prevalence?

Answer 19

• provide an idea about the ‘burden of disease
• know the need for particular health services
• know how many people with a characteristic, such as smoking in a given population

Question 20

What is morbidity rate?

Answer 20

number of existing or new cases of a particular disease per 100 population (note, not technically always a rate)

Question 21

What is Crude Birth Rate (CBR)?

Answer 21

The number of deaths per 1000 population.

Question 22

What is General Fertility Rate (GFR)?

Answer 22

General Fertility Rate (GFR): number of live births per 1,000 female population aged 15-44 years per year

Question 23

Define Age-specific fertility rate (ASFR)?

Answer 23

Age-specific fertility rate (ASFR): number of live births per 1000 women in a specific age group per year

Question 24

Define Total Period Fertility Rate (TPFR)

Answer 24

Total Period Fertility Rate (TPFR): the average number of children that would be born to a hypothetical woman in her life i.e. the sum of current age-specific fertility rates

Question 25

Define Life expectancy:

Answer 25

Life expectancy is the average number of years that a newborn is expected to live if current mortality rates apply

Question 26

Infant Mortality Rate (IMR) equation

Answer 26

IMR = Number of deaths per year occurring

within the first year of life x 1000

Total number of live births in the year