Sources of routine data and standardisation

Question 1

why do we need routine data?

Answer 1

to measure disease prevalence by groups of persons at risk, place and time.

to plan/assess disease prevention and patient management strategies.

Question 2

advantages of routine data?

Answer 2

• often covers large populations, even whole countries
• readily available
• cheap as already collected

Question 3

uses of routine data?

Answer 3

• to generate hypotheses
• to assess a population and describe its baseline characteristics
• to estimate disease prevalence or incidence of events

Question 4

disadvantages of routine data?

Answer 4

• often not up to data
• can be incomplete (except for Census)
• variable of interest may not be collected
• can be influenced by political pressure or financial constraints.

Question 5

name sources of routine data

Answer 5

• population (census, registers)
• civil registration (births, marriages, deaths)
• morbidity (disease reg, GP records, surveys)
• other (educational records, housing records)

Question 6

give examples of population-based surveys used as sources of routine data

Answer 6

• Scottish Health Survey
• General household survey
• Living costs and food survey

Question 7

how is crude mortality rate calculated?

Answer 7

total no. of deaths / total population at period of specific time

Question 8

what do crude mortality rates depend on?

Answer 8

• age/sex structure of the populations

e.g. a country with a higher proportion of old people will have a higher number of deaths and a higher crude mortality rate

Question 9

what is standardisation used for?

Answer 9

to control for confounding effects of age so that rates of disease or mortality can be compared in populations with different age structures.

Question 10

what is indirect standardisation?

Answer 10

finding the number of deaths expected if both populations had the same age specific death rates, but kept their real age structure.

Question 11

what do you need to calculate indirect standardisation?

Answer 11

the age-specific mortality rates for a standard population

the age structure of the study populations

the total number of deaths in the study populations

Question 12

what is the standard mortality ratio?

Answer 12

a measure, expressed as either ratio or percentage, to quantify an increase or decrease in mortality in a study cohort compared to the general population.

Question 13

how is SMR calculated?

Answer 13

SMR = number of observed deaths / number of expected deaths

Question 14

advantages of direct standardisation?

Answer 14

• less bias
• better when comparing more than 2 groups with different age distributions

Question 15

disadvantages of direct standardisation?

Answer 15

need age specific rates for study populations and these are not always available or reliable

in small sub-populations with few cases, indirect method is preferred over direct method

Question 16

advantages of indirect method of standardisation?

Answer 16

only need total observed cases/deaths in study population and its age structure

Question 17

disadvantages of indirect standardisation?

Answer 17

SMR depends on age distribution of study population

SMRs can only be compared between populations with similar age structure