you decide that you want to examine the lead concentrations in blue crabs in the Chesapeake...

you decide that you want to examine the lead concentrations in blue crabs in the Chesapeake Bay. Before you collect the crabs, you would like to determine how many crabs should be in your sample. You decide on a Type I error rate of 0.05 and want to achieve power of 0.80. Based on previous studies you assume a population standard deviation of 0.10 ug Pb/g crab. You want to be able to detect an effect size of 0.01 ug Pb/g crab (assume a one-sided test). How many crabs should you include in your random sample?

Expert Solution

Level of Significance ,    α =    0.05
std dev =    σ =    0.100
power =    1-ß =    0.8
ß=       0.2
δ=      0.01

Z ( α ) =       1.6449   [excel function: =normsinv(α)

Z (ß) =        0.8416   [excel function: =normsinv(ß)

sample size needed =    n = ( ( Z(ß)+Z(α) )*σ / δ )² = ( (   0.8416   +   1.6449   ) *   0.1   /   0.01   ) ² =   618.2557

so, sample size =        619

milcah answered 9 months ago

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