Unformatted text preview: Expected frequency = expected proportion * n o X 2 equals sum of squared differences between expected and observed frequencies divided by expected frequency o X 2 =∑(OE) 2 /E X 2 (k,n) o The degrees of freedom for X 2 equals # of deviations btwn observed and expected values that are free to vary Goodness of fit X 2 : df=k1 o Twoway contingency tables Expected frequency (in each cell)=nCOL(proportionROW) proportionROW=nROW/n expected frequency=nCOL(nROW/n) df = # outcomes minus one (C1) * # groups minus one (R1) • df=(C1)(R1) • AVOID computing X 2 if: o More than 20% of cells have expected frequency of 5 or less o Any of the cells have an expected frequency of 3 or smaller o ∑(OE) 2 /E; if using E, we are giving disproportionate weight to very unstable (low frequency) cells o Observations have to be independent for X 2 – cannot use for X 2 related (repeated) measures....
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 Spring '11
 Ackroff
 null hypothesis model, expected frequency

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