Statistics

Question 1

a person is defined as blind by the World Health Organization if

Answer 1

visual acuity (VA) of 3/60 in the better eye, or a central visual field of 10 ̊

Question 2

“person has severe visual

impairment (SVI)”

Answer 2

VA is 6/60–3/6

Question 3

Prevalence estimates

Answer 3

“are used to calculate the

expected number of people with disease in the population.”

Question 4

Measures of Incidence

Answer 4

cumulative incidence (number of new cases that occur in a population wich is disease free at baseline) and incidence rate (person time at risk as the denominator)

Question 5

Relative risk

Answer 5

“value of 1.0 indicates no association between
exposure and disease. A value >1.0 shows that there may be a positive association between exposure and disease (exposure may cause disease), and a value <1.0 indicates an inverse association between exposure and disease (exposure may protect from disease).”

Question 6

Chance

Answer 6

Can be measured by confidence intervals, cannot be prevented, can be reduced by an adequated sample size

Question 7

Confouding

Answer 7

Can be reduced by good study design, and taken account of during data analysis

Question 8

Bias

Answer 8

Effect on findings cannot be measured, can be reduced by good study design (selection bias) and quality control during study (information bias), not influenced by data analysis

Question 9

Selection bias

Answer 9

” is the error caused by

systematic differences in characteristics between those who take part in a study and those who do not”

Question 10

Information bias

Answer 10

“is caused by inaccuracy in the measurement of exposure or disease that results in different quality of information between comparison groups”

Question 11

Causation

Answer 11

“If the effects of confounding, chance, and bias are ruled out
then causation becomes a possible explanation for the
exposure disease association.”

Question 12

Cross sectional survey

Answer 12

“measure the prevalence of
disease, so that the burden of disease can be estimated. To
conduct a cross sectional survey, we carefully sample the desired number of study participants and examine and/or interview them to determine whether they have the disease and exposure(s) of interest.”

Question 13

Cohort study

Answer 13

“Cohort studies allow us to measure predictors of disease
incidence. A group of people free from the disease of interest are recruited and characterised as ‘‘exposed’’ or ‘‘unexposed’’ with respect to the risk factor under investigation. cohort studies expensive and time consuming”

Question 14

Case-control studies

Answer 14

” used to study the aetiology of
disease. Case-control studies are conducted by recruiting
people who have the disease of interest (cases) as well as
people without the disease (controls). Case-control studies are relatively quick and cheap to carry out.”

Question 15

Randomised controlled trials

Answer 15

” is an intervention study
that forms a special subset of cohort studies. RCTs are
typically used to assess the benefit of a new drug or
treatment, but they are also useful for evaluating the impact of a preventive measure (for example, health education). In an RCT, people are selected and randomised to receive either the intervention (treatment under investigation) or the control (placebo or standard treatment). he only difference
between them is that one group receives the intervention while the other does not. gold standard of study designs. expensive, take a long time to
generate results, and can only be used to answer certain types of questions.”