Vector sampling

Question 1

Are local people still at risk even if the vector is not found?

Answer 1

Just because it is not found doesn’t mean it is not present and that people are not at risk.

Question 2

Define sensitivity of vector sampling.

Answer 2

The probability of detecting at least one vector in a site that is actually infested.

Question 3

Define the specificity of vector sampling.

Answer 3

The probability of detecting no vectors in a site that is actually not infested.

Question 4

What is the Naïve estimate (the WHO index for vector presence) equation?

Answer 4

no of times vector found/ no of locations checked

Question 5

Why is the WHO index for vector presence not an ideal measurement?

Answer 5

It does not take into account that the sensitivity of sampling may be (and almost always is) less than 100%. May miss vectors in sites that are actually infested and wrongly say that they are not infested.

Question 6

What type of statistical analysis would be used to analyse the true positives and negatives and false positives and negatives when sampling vectors?

Answer 6

Regression analysis.

Question 7

What do likelihood-based methods estimate? RE vector population sampling?
How is this carried out?

Answer 7

Used for estimating site occupancy.

Measure covariates (e.g. measure all other variables that may be contributing to the outcome such as environmental conditions etc).–> Consider all the variates to inform relationships.

Question 8

Which type of sampling provides results higher than the WHO gold standard?

Answer 8

Model-based estimates.

Question 9

What are the three types of spatial distribution?

Answer 9

• CLustered- vectors are often clustered and parasites very very clustered
• Random (poisson)
• Regular- e.g. if found in every house

Question 10

When making a hypothesis about sampling vectors what would the H0 be?

Answer 10

That the distribution is spatially random. (Ha=there is spatial autocorrelation i.e. clustering of some kind).