Ap stats unit 1

Quantitive variable

takes numerical values for a measured quantity

Categorical variable

takes values that have category and label names

bar graphs

shows frequencies or relative frequencies

Two way table frequency calculations

marginal: B/C

Joint: A/C

conditional : A/B

Segmented bar graph

stacks bars to make up 100%

mosaic plot

segmented bar graph where the bars in the graph are proportional to the group size

Association definition

knowing the value of one variable helps us predict the other variable

Dotplots

represents every individual value on a simple scale

Stem plots

data representation where each data point is shown as a marker on a “stem” like structure

Histograms

Shows general shape of data

Variance

(Standard deviation)²

Desribing a distribution

Shape, outliers, center, variability (range)

Outliers

Mean and standard deviation are greatly affected, median is resistent. Skewed or outliers use median or IQR to describe center but if not use mean

Outlier calculation

mean-2d, mean+2d or Q1-1.5IQR and Q3+1.5IQR

boxplots and 5 number summary

minimum, quarter 1, median, q3, max

percentile

example: being in the 95th percentile means you are better then 95% of all people in that section

Cumulative relative frequency graph

Proportion on y axis, x axis have Q1, median and q3

Z score

value-mean/SD, z scores show position of a value relative to other values using standard devations above or below the mean

Linear transformations

addition or subtraction, variablility and shape stay the same but for multiplciation and division use the same procedures, shape also stays the same

Density curves

total area= 1

skewed right: mean>median

skewed left: median>mean

Empirical rule

68, 95, 99.7 proportions in a normal dist

Normal dist calculation for probability

normalcdf(lower, upper, mean, sd)

Normal dist calculation for area

invnorm