Session 2 Flashcards
What are the types of Variable?
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)
How can you express continuous vs categorical data?
Histogram: continuous
Bar chart: discrete
Define Mode?
Mode the value (or group of values) which occur most often i.e. the highest peak of a histogram.
What is the median?
Median the middle value (so arrange in order of size, (n+1)/2th observation if odd or n/2th, if even.
Define mean
Mean (average) arithmetic average of observations, mean = (x1 + x2+…+xn)/n
what does a symmetrical distribution tell you?
Symmetrical distribution: mean = median
What does a skewed distribution tell you?
Skewed distribution:
right: mean > median
left mean < median
What is Interquartile range (IQR)?
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.
What is standard deviation?
SD: measures the spread in data around the mean
What is Variance?
What are the methods of presenting and summarizing data?
Define incidence
Incidence the number of new cases per population at risk in a given time period
Define prevalence
Prevalence the number of all (new + old) cases per population at a given time
How do you calculate incidence
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 %
How do you calculate incidence density and when is it used for?
- 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
Why is calculating the incidence useful?
- 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
What is prevalence?
- focuses on health status
- is the proportion of a population in a particular health state
How do you calculate Prevalence?
Prevalence = number of cases at a given time
number in the population at that time
Why is it important to calculate prevalence?
- 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
What is morbidity rate?
number of existing or new cases of a particular disease per 100 population (note, not technically always a rate)
What is Crude Birth Rate (CBR)?
The number of deaths per 1000 population.
What is General Fertility Rate (GFR)?
General Fertility Rate (GFR): number of live births per 1,000 female population aged 15-44 years per year
Define Age-specific fertility rate (ASFR)?
Age-specific fertility rate (ASFR): number of live births per 1000 women in a specific age group per year
Define Total Period Fertility Rate (TPFR)
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
Define Life expectancy:
Life expectancy is the average number of years that a newborn is expected to live if current mortality rates apply
Infant Mortality Rate (IMR) equation
IMR = Number of deaths per year occurring
within the first year of life x 1000
Total number of live births in the year
