stat 1222 module 1

Population

Who/what we want to know about

Sample

Who/what we actually surveyed, subsection of the population

Qualitative

Categorical, typically in words, sometimes not (ex. Zipcodes)

Quantum Discrete

Numerical but only countable (1, 2, 3, …)

Quantitative Continuous

Numerical but any value, can be decimals, measurements

6 sampling techniques

1. Simple Random Survey

2. Systemic

3. Cluster

4. Convenince

5. Stratified

6. Voluntary response

Simple random sample

Names from hat

Systemic

Every 5th person

Cluster

Randomly select a group, then sample the whole group

Stratified

Randomly select some people from each group

Convenience

Easiest, closest to you

Voluntary response

Online poll

Skewed left

Tail to the left, mean less than median

Skewed right

Tail to the right, mean greater than median

Symmetric

Bell curve, mean equals median

Mean

Average of the data

Median

Middle, 50/50

Mode

Value that occurs most often

What happens to the mean if a large number is taken away

The mean will decrease

What happens to the mean if a small number is taken away

The mean will increase

Standard deviation

=stdev.s(range) or =stdev.p(range)

Tells how spread out the data is, the average distance each point is from the mean

What is the best measure of center

Use the median if data is skewed

If the data is symmetric use the mean

Percentiles

The amount that is less than or equal to a data point

Z score

=(x-m)/stdev

tells you how many standard deviations you are above or below the mean

Negative is below the mean

Positive if above the mean