# EXAM-3-CHEAT-SHEET - EQUATIONS Standard Deviation s= y y n1...

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EQUATIONS:Standard Deviation: s=(y− ´y)2n1Variance : s2=(y−´y)2n1Z-score: z=y−´yswhere s is standard deviation and ȳ is the mean or z=x−´µσComplement Rule: P(A) = 1 – P(AC)Multiplication Rule: P(A and B) = P(A) X P(B), provided that A and B are independent General Multiplication Rule: P(A andB) = P(A) X P(B|A) for any 2 events A and B; doesn’t require independenceAddition Rule (disjoint): P(A or B) = P(A) + P(B), provided that A and B are disjointedGeneral Addition Rule: P(A or B) = P(A) + P(B) – P(A and B) for any two events A and BConditional Probability: P(B|A)=P(AB)P(A)The probability of B givenAIndependence: P(B|A) = P(B)Expected Value: E(X) = ∑xP(x)σ2= Var(X) = ∑(x-µ)2P(x)σ = SD(X) = Var(X)Random Variable: Adding/Subtracting: E(X ± c) = E(X) ± c; Var(X ± c) = Var(X); SD(X ± c) = SD(X)Multiplying by a value: E(aX) = aE(X); Var(aX) = a2Var(X); SD(aX) = |a|SD(X)Addition Rule for Expected Values of Random Variables: E(X ± Y) = E(X) ± E(Y)Addition Rule for Variances of (Independent) Random Variables: Var(X ± Y) = Var(X) + Var(Y) if X and Y are independentCH 2 – DATARows of a data table generally correspond to the individual cases about which we’ve recorded some characteristics (variables)Quantitative– numerical value with units that you could do arithmetic onCategorical– number of other value that represents a category for the caseOrdinal– name categories for which there is an intrinsic orderNominal – name categories that don’t have a particular orderIdentifier– variable that helps uniquely identify a record and combine data from different placesTime series– a single variable measured at regular intervals over time (months, quarters, or years)Cross-sectional– where several variables are measured at the same time point (Ex: expenses for a month at each Starbucks)CH 3 – SURVEYS AND SAMPLINGGiven a population, we want to estimate the value of a parameter(property of population)Identify a sampling frame(part of the population we can get access to) and sample from thatCompute the sample statisticto estimate the population parameterSimple random sample (SRS)– a sampling method that gives each combination of individuals an equal chanceSample Methods – Stratified random sampling, Cluster sampling, Multistage sampling, Systematic sampling Nonresponsive bias– bias introduced to a sample when a large fraction of those sampled fails to respondVoluntary response bias– surveys in which respondents volunteer to participateVoluntary response sample– a large group of individuals is invited to respond, and all who do respond are countedConvenience sampling– using individuals who are convenientUndercoverage – some portion of the population is not sampled at all or has a smaller representation in the sample than it has in the populationCH 4 – CATEGORICAL DATAArea Principle
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