Ap Stats

What are data?: Infomation/ values with CONTEXT

Population of interest: The “who” we want to learn about

Sample: The subset that we collect data from

Variables: The “what”


TYPES OF DATA

  • Categorical (qualitative) data

  • Quantitative data


  1. Categorical data: Answefs questions that fall into categories. Can use word labels or number labels. Ex: Zipcode, favorites, color - to display categorical data, you can make bar charts, pie charts, or segmented bar charts depending on the data.

Categorical data condition: making sure data are appropriate for the graph you want to display.

  1. Quantitative data: Answers questions about the quantity of what’s being measured. It is composed of numerical values. - can be displayed on dot plot, box plots, or histograms, stem and leaf plot

    1. Discrete Data: Takes whole number when being collected. Ex: Books read in a month

    2. Continuous: Can be a decimal number. Ex: height, weight

Quantitative Data Condition: Data are values of a quantitative variable whole UNITS are known.

Frequency tables: used to organize categorical data. They display categorical names and counts.

Relative frequency tables: display categorical names but give percentages instead of counts .

  • Both frequency tables and relative frequency tables describe the frequency distributions of categorical data.


HOW TO DESCRIBE A DISTRIBUTION

C: Center - Mean, Median

U: Unusual features (Gaps, outliers, grouping)

S: Shape ( Uni, bi, Multi-modal/ Uniform/ Symmetric, skewed left, skewed right)

S: Spread - Standard deviation (how spread out data are), range, IQR

D: Description need CONTEXT

It is very important to be able to provide statistical measures when describing quantitative distributions.

  • For unimodal and symmetric distributions, the center and spread are described with the mean and standard deviation

  • For skewed, multi-modal or distributions with outliers, the mean and IQR is used to describe the center and spread.

Q1 is known as the 1st quartile, the 2th percentile

The median is know the the Q2, and the 50th percentile

Q3 is known as the 75th percentile or the 3rd quartile

  • if a distribution is skewed left the mean is lower than the median. If the distribution is skewed right then the mean is higher than the median.