Sampling Methods to Detect Disease Flashcards

Comprehensive practice questions covering sampling methods, surveillance types, diagnostic test properties (Sensitivity/Specificity), and error analysis in veterinary epidemiology.

What is the primary difference between monitoring and surveillance according to the lecture?

Monitoring is the routine collection of information to know what is normal ('watching'), whereas surveillance is more active with the purpose of detecting, controlling, or eradicating disease ('looking for trouble').

In the context of MOSS (Monitoring and Surveillance Systems), what are the four main uses listed?

Animal health, public health, animal welfare, and international trade.

What are the characteristics of active surveillance?

Investigators actively collect data (e.g., blood sampling cattle). It is accurate and detects more disease but is expensive and labour-intensive.

What are the common disadvantages of passive surveillance?

Under-reporting, inconsistent data, and the tendency to miss cases.

According to the transcript, what is the flow from a pathogen to a diagnostic complex?

Pathogen $\rightarrow$ Antigen $\rightarrow$ Antibody production $\rightarrow$ Antigen-antibody complex.

How is Sensitivity ($Se$) defined in veterinary diagnostics?

The ability of a test to correctly detect diseased animals; it results in few false negatives and is 'good at finding disease'.

How is Specificity ($Sp$) defined in veterinary diagnostics?

The ability of a test to correctly detect healthy animals; it results in few false positives and is 'good at confirming disease'.

What are the exam rules 'SNOUT' and 'SPIN' used for?

SNOUT: Sensitive test Negative rules OUT disease. SPIN: Specific test Positive rules IN (confirms) disease.

What is the difference between a screening test and a diagnostic test?

A screening test is used in apparently healthy animals to find hidden disease, while a diagnostic test is used when disease is suspected to confirm the diagnosis and guide treatment.

Define the 'Target Population' and the 'Study Population'.

Target Population is the population you want to draw conclusions about (e.g., outdoor pigs in Devon). Study Population is the animals actually tested (e.g., 100 pigs sampled from Devon farms).

What is a 'Sampling Frame'?

A list of all individuals that could be sampled, such as a herd list, farm database, or animal register.

What is the difference between systematic sampling and stratified sampling?

Systematic sampling involves choosing every nth animal (e.g., every 10th cow). Stratified sampling involves dividing the population into groups (e.g., calves, heifers, adult cows) and sampling from each group.

What are the three types of non-probability sampling mentioned?

Convenience sampling (easiest to access), purposive sampling (chosen deliberately), and haphazard sampling (no organised method).

Differentiate between Variance and Bias in sampling.

Variance (random error) occurs by chance and can be measured by confidence intervals. Bias (systematic error) is predictable, results in consistently wrong data, and must be prevented by good study design.

Define Accuracy and Precision.

Accuracy is how close a result is to the true value. Precision is how repeatable or consistent the result is.

What are the two primary ways to reduce variance in a study?

Increase the sample size and use a better sampling strategy (e.g., stratified sampling).

What is a 'Gold Standard' test?

An ideal test that detects all true positives, all true negatives, and has no misclassifications.

What is 'Power' in the context of disease sampling?

The chance of detecting a true effect; it increases as the sample size increases.