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Epidemiology in Practice > Tools of the trade > Flashcards

Flashcards in Tools of the trade Deck (33)
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1
Q

what is null hypothesis

A

no significant difference`

2
Q

what is P value

A

If p<0.05 statistically significant (reject null hypothesis), if p>0.05 no significant difference.

3
Q

(95%) Confidence interval

A

an estimated range of values calculated from a given set of sample data which are likely to contain the ‘true’ population value. If value falls between the range can say “95% sure the result is not due to chance”

4
Q

what is Attributable Risk

A

Incidence in the exposed – Incidence in the unexposed/100

5
Q

what is relative risk

A

Incidence in the exposed/ Incidence in the unexposed

6
Q

what is the incidence in exposed

A

A/(A+B)

A is cases exposed, B is non- cases exposed

7
Q

what is the incidence in unexposed

A

C/(C+D)

C is cases non exposed, D is non-cases exposed

8
Q

why is the attributable risk useful

A

its useful in evaluating the impact of introduction or removal of risk factors. Its value indicates the number of cases of the disease among the exposed group that could be prevented if the exposure were completely eliminated.

9
Q

what is the relative risk used for

A

used as a measure of association between an exposure and disease.

10
Q

what does it mean if relative risk is less than 1

A

risk of outcome among exposed is less than risk of outcome among the not exposed. the exposure is associated with a lower risk of the outcome.

11
Q

what does it mean if relative risk equals 1

A

indicates that the incidence of disease in the exposed and the unexposed are identical and thus the data shows no association between the exposure and the disease.

12
Q

what does it mean if relative risk is more than 1

A

risk of outcome among the exposed is greater than the risk of outcome among the not exposed. the exposure is associated with a higher risk of the outcome

13
Q

define odds ratio

A

odds of exposure among cases/odds of exposure among controls.

14
Q

Odds ratio =

A

it equals (AxD) / (BxC). A is exposed cases, B is exposed controls, C is non exposed cases and D is non exposed controls

15
Q

what does it mean if odds ratio = 1

A

no association

16
Q

what does it mean if odds ratio is greater than 1

A

positive association between exposure & disease. The exposure is associated with increased risk of disease

17
Q

what does it mean if odds ratio is less than 1

A

inverse association b/t exposure and disease. The exposure is associated with reduced risk of disease.

18
Q

the lower the P value

A

the less likely that the estimated difference is a chance finding

19
Q

what is a case

A

an individual with the outcome under study (in a casecontrol study

20
Q

what is a case control study

A

study in which individuals are selected on the basis of whether or not they have the outcome of interest; usually some relatively rare outcome. Exposure status is explored to establish whether the exposure is more common in the case or control group. This type of study always results in an odds rati

21
Q

what is count

A

the most basic measure of disease frequency is a simple count of affected individuals. The number (count) of cases that occurred in a particular population is of little use in comparing populations and groups.

22
Q

what is a chi squared test

A

– a statistical procedure for testing whether two proportions are similar

23
Q

what is a cohort study

A

tudy in which individuals are selected on the basis of exposure status and are followed over a period of time to allow the frequency of occurrence of the outcome of interest in the exposed and non exposed groups to be compared

24
Q

what can we say for a 95% confidence interval of 1.2 – 3.4

A

hat we are 95% confident that the true value of risk will not be lower than 1.2 and will not be higher than 3.4.

25
Q

what is a confounding variable

A

a factor that is associated with both the exposure and outcome of interest

26
Q

what does exposure mean

A

when people have been ‘exposed’, they have been in contact with something that is hypothesised to have an effect on health

27
Q

Population attributable risk (also known as the population excess risk)

A

a measure of the risk of outcome in the study population which is attributable to the exposure of interest.

28
Q

Population excess fraction (also known as the population attributable fraction)

A

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

29
Q

Regression

A

a method for controlling the effect of confounding at the analysis stage of a study - statistical modelling is used to control for one or many confounding variables

30
Q

Stratification

A

a method for controlling the effect of confounding at the analysis stage of a study - risks are calculated separately for each category of confounding variable, e.g. each age group and each sex separately.
61

31
Q

Standardisation

A

a method for controlling the effect of confounding at the analysis stage of a study.

32
Q

Restriction

A

a method for controlling the effect of confounding at the design stage of a study, e.g. by including
60 patients in a clinical trial only between the ages of 18 and 65 without pre-existing illness so that the results of the trial are not confused (‘confounded’) by different levels of age or morbidity in the two treatment groups.

33
Q

matching

A

a method for “controlling for” the effect of confounding at the design stage of a case-control study; controls are selected to have a similar distribution of potentially confounding variables to the cases