Stats exam 2 mega deck

Measuring

assigning a numerical value to represent a property

instrument

thing used to make a measurement

Valid Variables/Measurement

If it is relevant and appropriate as a representation of the property.

Predictive validity

extent to which a test or measurement accurately forecasts future outcomes

Count

Total amount of occurences

Rate

Frequency of those occurrences over a specific time period, often a better measurement than counts

Bias

systematic over- or under estimation of the value of a variable

random error and measurements

measurements have random error when repeated measurements give different results

Variance

How much random error an instrument has

Reliable measurement

has small random error

x̄

Sample mean

deviation

distance of a point from the mean

Variance formula

Standard deviation

average distance of points from the mean

Standard deviation formula

What does a smaller deviation mean?

More consistency

distribution

the possible values that a variable takes on and how often it takes on these values.

Pie chart usage scenarios

When the number of categories is reasonably small(5 or under), and they should each be part of a whole.

Bar chart rules

Vertical axis must start at 0

Bars must have same width

Bars can’t touch, lets you know variable is categorical

Bar chart usage

When comparing larger quantities

timeplot usage

to show how the value of a numerical variable changes over time

Histogram usage

with numerical, especially continuous data with many possible values

Stemplots usage

Numerical, smaller data, allowing for a more detailed view

Stem and leaf example

143

stem would be 14, leaf would be 3

Center

middle of a distribution

Spread

how far the numbers can get from each other

Symmetric shape

left and right sides of the distribution are mirror images

Skewed left

left tail is longer than the right

Skewed right

right tail is longer than the left

Irregular shape

neither skewed nor symmetric

Mode

high point in the distribution, can be uni, bi, or multimodal

Outliers

are individuals which fall outside of the general pattern of the graph

Median

is the 50th percentile of a data set, half the data is above and half is below

Measures of center

Mean and median

percentile

Percent where the rest of the data is at or below

5 number summary components

Minimum

1st Quartile(25 Percentile)

2nd Quartile/Median

3rd Quartile (75 Percentile)

Maximum