Research Methodology 4: Stats 2

Question 1

define prevalence

Answer 1

Prevalence measures the frequency of “cases” in a given population at a designated time

Question 2

what kind of study measures prevalence

Answer 2

cross sectional

Question 3

what does a cross sectional study meausure

Answer 3

prevalence and exposure

Question 4

what ca you calculate from a cross sectional study

Answer 4

point prevalence

Question 5

pros of cross sectional study

Answer 5

Measure prevalence and thus disease burden in whole population and subpopulations
Can compare prevalence in exposed and non-exposed to risk factors
Quick and inexpensive
Can be used to initially explore a hypothesis, prior to another type of study

Question 6

cons of cross sectional

Answer 6

Not suitable for rare diseases
Not suitable for diseases of short duration
Cannot separate cause and effect as they are measured at the same time
Cannot measure rate of new cases arising and any changes therein

Question 7

what do cohort studies measure

Answer 7

A group of people is followed through time, and the onset of a disease/health event measured.

Question 8

what can you calculate from a cohort study?

Answer 8

incidence

Question 9

what is the relative risk ?

Answer 9

incidence of disease in exposed/ incidence of disease in non-exposed.

Question 10

what does the number tell you for relative risk

Answer 10

<1 = less risk than those not exposed
1= same risk
>1 risk in exposed greater than non

Question 11

pros of a cohort study

Answer 11

Can calculate incidence and relative risk
Can offer some evidence of cause – effect relationship i.e. impact of exposure on disease
Can identify more than one disease related to single exposure (and positive outcomes of exposure/s as relevant)
Good when exposure is rare
Minimises selection and information bias

Question 12

cons of a cohort study

Answer 12

Potential for losses to follow-up (attrition may differ in exposed versus unexposed / disease versus non, the longer the follow-up the greater the risk of attrition)
Often requires large sample, can take a long time to complete
Less suitable for rare diseases
Expensive
If retrospective, data availability and quality may be poor

Question 13

what is a case control study

Answer 13

Case–control study  groups who differ at outset on disease (condition/outcome) status

Question 14

pros of a case control

Answer 14

Can offer some evidence of cause – effect relationship i.e. impact of exposure on disease
Can identify multiple exposures (both positive and negative associations, interactions)
Good when disease/outcome is rare
Minimises selection and information bias
Retrospective - cheaper and typically shorter in duration

Question 15

cons of a case control

Answer 15

Cannot calculate prevalence or incidence
Less suitable for rare exposures
Can be hard to ensure exposure occurred before onset
Retrospective data availability and quality may be poor
Suitable control group may be difficult to find

Question 16

how do we calculate risk

Answer 16

Risk = outcome of interest / totalnumber of all possible outcomes

Question 17

how do we calculate odds?

Answer 17

Odds = outcome of interest / outcomes not of interest

Question 18

how do we calculate odds ratio?

Answer 18

Odds ratio = odds in exposed / odds in non-exposed

Question 19

define confidence interval

Answer 19

The confidence interval describes the range of values with a given probability (e.g. 95%) that the true value of a variable is contained within that range.

Question 20

define PPV

Answer 20

Positive Predictive Value (PPV) = likelihood patient with positive test result actually has the disease

Question 21

define NPV

Answer 21

Negative Predictive Value (NPV) = likelihood patient with negative test result does not have the disease