measures of occurrence

Question 1

what are rates used for in terms of disease?

Answer 1

they are used to quantify and compare disease in populations

Question 2

what is epidemiology?

Answer 2

how often diseases occur in different groups of people and why - measure of disease outcome in population at risk

Question 3

what is the PHE UK?

Answer 3

it expresses a risk as a rate per 100,000 population

Question 4

what is the incidence of a disease?

Answer 4

it is the rate at which new cases occur in a population over a specified time period - it must include time unit

Question 5

what is the incidence rate equation?

Answer 5

incidence rate = number of new cases in the time period / number at risk in population during that period

Question 6

define prevalence?

Answer 6

prevalence is the proportion of existing cases - old and new (it is not the risk or rate of disease)

Question 7

what is point prevalence?

Answer 7

it is the proportion of existing cases in a population at a period of time

Question 8

how can the point prevalence be estimated?

Answer 8

incidence rate x average duration of disease - only measurable from cross sectional surveys therefore it is newly diagnosed cases + people who have already got the condition

Question 9

what is in migration and how is it related to prevalence?

Answer 9

they are people who have moved into an area who have the disease but are not yet diagnosed therefore they are incidence cases that move into the prevalence pool

Question 10

what is removed from the prevalence pool?

Answer 10

out migration, death and cures

Question 11

define mortality?

Answer 11

it is the incidence of death from a disease

Question 12

what is the equation for mortality rate?

Answer 12

number of people who die from the disease in a time period/ the number of people in the population in the period

Question 13

what is ascertainment?

Answer 13

it means that you have counted all of the individuals of interest in your study

Question 14

what is a denominator?

Answer 14

number of persons in the population at the start of the observation period

Question 15

what rate refers to the population as a whole?

Answer 15

crude rate

Question 16

how is standardisation used?

Answer 16

it is used to compare two different area with different population structures - mainly done by sex and age

Question 17

how many methods of standardisation is there?

Answer 17

two - direct and indirect

Question 18

what is direct standardisation?

Answer 18

it involved applying the rates of disease observed in the study group to the standard population

Question 19

what is age standardised rates?

Answer 19

it is the weighted average of age specific rates

Question 20

how would you conduct direct standardisation for age?

Answer 20

apply the same weighting to every area and age groups, add up and get a total for age standardised rates

Question 21

what would you use if it was an international study?

Answer 21

world standard population

Question 22

what is indirect standardisation?

Answer 22

it is when you apply the rates of disease of the standard group to the study group - compares observed to expected - usually presented as ratios

Question 23

what is the equation for standardised mortality ratio?

Answer 23

SMR = observed number of deaths / expected number of deaths - often presented as a percentage

Question 24

why is age standardisation important?

Answer 24

areas with high mortality are different when standardised and unstandardised. When you take age into account the high observed mortality may actually be low.

Question 25

what is the secondary attack rate?

Answer 25

the number of new cases among contacts with a denominator of total number of contacts

Question 26

what is period prevalence?

Answer 26

the proportion of existing cases over a period of time with a denominator of average or mid-interval population