# stat 202 cheat sheet

**Topics:**Standard deviation, Skewness, Normal distribution

**Pages:**3 (509 words)

**Published:**October 11, 2013

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

oSpread – range of data

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...

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