# stat 202 cheat sheet

Topics: Standard deviation, Skewness, Normal distribution Pages: 3 (509 words) Published: October 11, 2013
Statistics – body of principles and procedures developed for collecting, summarizing, and interpreting data
Chapter 1
Distribution – describes what values the variable takes and how often –Pie Charts/Bar Graphs – categorical
Histograms/Stem plots – quantitative
Data set has info on number of individuals
For each individual, data gives values for variables
When looking at graph…
oCenter – middle of data
oShape – symmetry or skewed
Chapter 5
Regression used to predict data
¬¬¬ , least-squares regression line
opasses through (x, y)
ob = r (Sy/Sx), a = y – bx
r2 = fraction of variation in one variable that is explained by least-squares on the other variable –Extrapolation – values in regression outside of data range –Correlation ≠ Causation

Chapter 2
Numerical summary provides center & spread
Mean & median are different (average/midpoint)
Five-number Summary – min, Q1, M, Q3, max
oOutlier = 1.5 x (Q3-Q1) ± Q1/Q3
Variance (s2) and Standard Deviation (s) measure spread of distribution, gets larger as spread increases –Median and quartiles are resistant, mean and standard deviation are not –Mean and standard deviation are for symmetric distributions –5-number summary is for skewed distributions

Chapter 3
Density curve has total area of 1, rel. freq/interval
oIdealized description of overall pattern, smoothens it out oMean of D curve is µ, st. dev is σ
oMean is balance point, range (-∞, ∞)
oµ = M for symmetric curves
oN(µ, σ) = N(0,1), 68-95-99.7 rule
oz = (x – µ)/σ
Chapter 4
x = explanatory variable
y = response variable
In scatter plot, find…
oDirection - +/- association
oForm – linear, curved, clustered
oStrength – how linear points are
Correlation r measures linear direction & strength
or > 0 positive, r < 0 negative
o-1 ≥ r ≥ 1
or = ±1, perfectly linear
or = 0, no linear relationship
or not affected by change of measurement, but...