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Marketing Research chp 8

STUDY
PLAY
Sample Size Determination
1. budget
2. rules of thumb (past experience, sampling error)
3. number of subgroups
4. traditional statistical methods
n = Z 2 σ 2/ D2
sampling size means: Z = level of confidence expressed in standard errors
σ = population standard deviation
D = Acceptable amount of sampling error
n = Z 2 [π (1-π)]/ D2
sampling size proportions: Z = level of confidence expressed in standard errors
π = the population proportion
D = acceptable amount of sampling error
X +/- Z * σx
confidence interval means: σx= σ/ √ n
π +/- Z * σ p
confidence interval proportions: σ p = √ (π)(1-π)/n