Tools of the trade

Question 1

what is null hypothesis

Answer 1

no significant difference`

Question 2

what is P value

Answer 2

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

Question 3

(95%) Confidence interval

Answer 3

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”

Question 4

what is Attributable Risk

Answer 4

Incidence in the exposed – Incidence in the unexposed/100

Question 5

what is relative risk

Answer 5

Incidence in the exposed/ Incidence in the unexposed

Question 6

what is the incidence in exposed

Answer 6

A/(A+B)

A is cases exposed, B is non- cases exposed

Question 7

what is the incidence in unexposed

Answer 7

C/(C+D)

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

Question 8

why is the attributable risk useful

Answer 8

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.

Question 9

what is the relative risk used for

Answer 9

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

Question 10

what does it mean if relative risk is less than 1

Answer 10

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.

Question 11

what does it mean if relative risk equals 1

Answer 11

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.

Question 12

what does it mean if relative risk is more than 1

Answer 12

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

Question 13

define odds ratio

Answer 13

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

Question 14

Odds ratio =

Answer 14

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

Question 15

what does it mean if odds ratio = 1

Answer 15

no association

Question 16

what does it mean if odds ratio is greater than 1

Answer 16

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

Question 17

what does it mean if odds ratio is less than 1

Answer 17

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

Question 18

the lower the P value

Answer 18

the less likely that the estimated difference is a chance finding

Question 19

what is a case

Answer 19

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

Question 20

what is a case control study

Answer 20

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

Question 21

what is count

Answer 21

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.

Question 22

what is a chi squared test

Answer 22

– a statistical procedure for testing whether two proportions are similar

Question 23

what is a cohort study

Answer 23

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

Question 24

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

Answer 24

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.

Question 25

what is a confounding variable

Answer 25

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

Question 26

what does exposure mean

Answer 26

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

Question 27

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

Answer 27

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

Question 28

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

Answer 28

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

Question 29

Regression

Answer 29

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

Question 30

Stratification

Answer 30

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

Question 31

Standardisation

Answer 31

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

Question 32

Restriction

Answer 32

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.

Question 33

matching

Answer 33

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