statistical terminology

Question 1

Attributable risk

Answer 1

how much greater frequency of disease is in exposed group compared to non-exposed group
assuming exposure is casual

Question 2

attributable risk =

Answer 2

incidence in exposed-incidence in non-exposed

Question 3

excess fraction =

Answer 3

incidence in exposed/incidence in non-exposed

Question 4

case

Answer 4

an individual with the outcome under study (have disease/illness/event)
not same as clinical definition

Question 5

count

Answer 5

number of cases that occurred in a population

useful in planning services, not for comparison

Question 6

chi squared test

Answer 6

statistical procedure fro determining if 2 proportions are similar

Question 7

cohort study

Answer 7

study where individuals are chosen on basis of exposure and followed over a period of time to allow occurrence of the exposure of interest
produces relative risk

Question 8

confidence interval

Answer 8

an estimated range of values calculated from a given set of sample data which are likely to contain the true population value
relative risk - cannot include 1
difference - 0?

Question 9

confounding

Answer 9

possible explanation for study finding if confounding variables have not been taken into account

Question 10

confounding variable

Answer 10

a factor associated with exposure and outcome of interest

Question 11

control

Answer 11

person without the outcome of interest or not receiving the intervention

Question 12

exposure

Answer 12

people come in contact with something hypothesised to have an effect on health - risk factors

Question 13

incidence

Answer 13

number of new cases of outcome of interest occurring in a defined population over a defined period of time
can be interpreted as probability that the individual will develop the disease in a given time

Question 14

matching

Answer 14

method for controlling for the effect of confounding at design stage of case control - controls have similar distribution of confounding factors to cases

Question 15

normal distribution

Answer 15

set of values and frequencies that describe many things - symmetrical distribution is foundation of many statistical tests because if know sd and mean - can draw every point on the curve

Question 16

null hypothesis

Answer 16

first stage in performing a statistical test
states there is no difference in the groups or that the rates are equal - relative risk = 1
odds ratio = 1 in case control study
rejected if the confidence interval doesn’t include the value expected under null ie 1 for RR or OR
for normally distributed groups - reject the null hypothesis if 0 - no difference between averages

Question 17

odds

Answer 17

way to express probability

Question 18

odds ratio =

Answer 18

odds of exposure in exposed/odds exposure in controls

Question 19

odds in terms of probability =

Answer 19

probability/(1-probability)

Question 20

odds ratio

Answer 20

for case control studies
ratio between 2 odds
good estimate of relative risk - which cant be measured because we don’t know incidence
1 - exposure no more likely in case or control
>1 exposure more likely in case - increase risk of disease
<1 exposure more likely in control - protective

Question 21

outcome

Answer 21

event or main quantity of interest in a particular study

Question 22

population attributable risk

Answer 22

population excess risk - measure of risk of outcome in study population attributable to the exposure of interest

Question 23

population excess fraction

Answer 23

population attributable fraction

measure of proportion (fraction) of cases observed in study population attributable to exposure of interest

Question 24

prevalence

Answer 24

number of cases of an outcome of interest in a defined population at a particular point in time - point prevalence
includes new and existing cases

Question 25

p-value

Answer 25

probability of obtaining the study result if null hypothesis is true smaller p value - easier to reject the null hypothesis

Question 26

randomisation

Answer 26

a method for ensuring both groups in a clinical trial have similar proportions of confounding variables eg age

Question 27

rate and risk

Answer 27

personal risk population rate both terms imply proportion

Question 28

rate and risk =

Answer 28

number of people with outcome of interest/number of people at risk of outcome

Question 29

regression

Answer 29

method for controlling effect of confounding at the analysis stage of te study statistical modelling is used to control for omne or many of the outcomes

Question 30

relative risk

Answer 30

measure of association between exposure and disease ratio of incidence rate in exposed group and incidence rate in non-exposed group 1 = incidence same in exposed and not exposed - data shows no association between exposure and disease >1 - positive association or increased risk among those exposed to the factor <1 - inverse association or decreased risk among those exposed - protective

Question 31

relative risk =

Answer 31

incidence in exposed/incidence in non-exposed group

Question 32

restriction

Answer 32

control confounding at design stage of the study

Question 33

sample

Answer 33

relatively small number of observations from which we try to describe the whole population from which the sample has been taken find mean of sample and use confidence interval to describe the range within which we think the population lies

Question 34

standardisation

Answer 34

control confounding at analysis stage | used to produce SMR

Question 35

statistical test

Answer 35

only way to decide if results are due to chance or are real take one value representing the observed difference between groups and compare against a table of appropriate mathematical distribution - eg normal distribution to see how extreme subtract population mean from value and dividing by the population standard deviation - look up result in table of standard normal deviation (mean 0, sd 1) to find out what proportion of values are greater than this

Question 36

stratification

Answer 36

method for controlling effect of confounding at analysis stage - risks are calculated separately for each category of confounding variable