Statistics

Question 1

The ideal sample should be selected at random. Why is this?

Answer 1

Makes the sample unbiased - each person/object has an equal chance of being picked
Makes the sample independent - if one person/object is chosen, it has no influence on another being chosen

Question 2

What are the different sampling methods?

Answer 2

stratified - divide population units into homogenous group (strata) and draw a simple random sample from each strata (e.g. population of all 20-50yr olds can be grouped according to SIMD - Scottish Index of Multiple Deprivation, and within each SIMD group, a simple random sample can be selected)
Clustered - groups population into small clusters, naturally occurring clusters (e.g. health boards, schools, practices), draws a simple random sample of clusters
Systematic - start with randomly chosen unit then select every nth unit, ok if pattern smooth over time
Convenience - avoid the bother of designing a procedure and just grab the first n population units that come along, especially prone to bias
Self-Selected - volunteers come forward, all sorts of problems can arise from these

Question 3

How can you create a sampling frame?

Answer 3

random number tables

computer generated random numbers

Question 4

How certain can we be that our sample mean is CLOSE TO the target population mean?

Answer 4

only select one sample
calculate 95% confidence intervals around the sampling mean
-95 times out of 100, the CI will contain the true population mean

Question 5

Interpretation of a confidence interval and data is only valid when?

Answer 5

the sample is a representative sample from the target population
the sample size is large enough for the distribution of the sample mean to be normal

Question 6

If a more precise estimate of the mean is required (i.e. a narrower CI interval), what would you do?

Answer 6

increase the sample size

Question 7

Why are confidence intervals used?

Answer 7

They allow us to generalise the result to the target population provided the sample is representative

Question 8

What should be assessed when looking at data?

Answer 8

How sampling is done - random?
Is sample representative - any biases?
Is sample large enough - look at width of confidence interval
Can findings be generalised to the target population?
Are the findings clinically important?

Question 9

The ______ the sample, the _______ the CI, the more accurate the mean.

Answer 9

larger

narrower

Question 10

What are the advantages of sampling a population?

Answer 10

lower cost
less time required
less resources needed