STATS250 LT 1 and 2

What is the difference between a population and a sample?

• Population: The entire group of interest in a study.

• Sample: A subset of the population that is actually observed or measured.

Random sampling:

Every member of the population has an equal chance of being selected.

Stratified sampling

Population is divided into subgroups (strata), and samples are taken from each stratum.

Why use stratified sampling?

Convenience sampling:

• Samples are taken based on ease of access (not random).

What are the types of variables?

Qualitative- Nominal or Ordinal

Quantitative- Discrete or Continuous

What is Qualitative

Categorical

Nominal- name, category as value ex. species

Ordinal- ranked variable, specific order to value of the variable ex 1st, 2nd, 3rd

Quantitative

Numeric

Discrete- countable values countably infinatew values often whole #s

Continuous- infinate number of possible values (decimals) ex. height/weight

σ=

population standard deviation

xi

each data point

μ

population mean

N

population size

s

sample standard deviation

xˉ

sample mean

n

sample size

What are the different biases

Non response bias-under coverage bias- response bias

Sample taken should have

The sample (ie. a wind turbine)

when taken

Where

Variable of interest and type

Measured

What is meant by a 99% confidence interval

We repeater the sample from the population 99% of samples will produce confidence intervals that capture the true mean