Estimating Mean And proportion

Question 1

Why does sample mean never be be exactly equal to population mean

Answer 1

Sampling error
Non -sampling error

Question 2

How does sampling error arise and how to reduce

Answer 2

Arise due to fact that we observed only part of the whole population
Increasing sample size

Question 3

Non sampling error with examples

Answer 3

Arise from flaw in sample selection, data management , data collection
Called systematic errors
Example
- loss of follow up
-observer error
-data processing ( entry , coding)
- equipment faults
-Low response rate
-convenience sample

Question 4

What is sampling distribution

Answer 4

Probability distribution of that statistic for samples of given size n taken from population

Question 5

When does sample mean have normal distribution

Answer 5

When variable has normal distribution in the population
Or
When sample size , n is large enough
Usually greater than or equal to 30

Question 6

Give important properties of central limit theorem

Answer 6

Sample mean is identical to population mean
Standard deviation of distribution of sample is equal to standard error of the mean (SEM)
If n is large enough , shape of sampling distribution is approximately normal

Question 7

Confidence intervals

Answer 7

A way of quantifying uncertainty in our estimate

Question 8

What is SEM

Answer 8

Standard error of mean