ok <- FALSE while(!ok) { pe <- round(runif(1, 0.05, 0.15), digits = 2) per <- round(runif(1, 0.6, 0.8), digits = 2) pnenr <- round(runif(1, 0.6, 0.8), digits = 2) prob1 <- pe * per prob2 <- pe * (1 - per) prob3 <- (1 - pe) * (1 - pnenr) prob4 <- (1 - pe) * pnenr tab <- cbind(c(prob1, prob3), c(prob2, prob4)) sol <- c(tab[1, 1] / sum(tab[, 1]), tab[1, 1] / sum(tab[1, ]), tab[2, 1] / sum(tab[2, ]), tab[1, 2] / sum(tab[1, ])) ok <- sum(tab) == 1 & all(tab > 0) & all(tab < 1) } tab2 <- cbind(rbind(tab, colSums(tab)), c(rowSums(tab), 1)) tab2 <- format(tab2 * 100, digits = 2, nsmall = 2, trim = TRUE) tab2 <- gsub(" ", "", tab2, fixed = TRUE) sol <- round(100 * as.vector(tab), digits = 2) lab <- c("E \\cap R", "\\overline{E} \\cap R", "E \\cap \\overline{R}", "\\overline{E} \\cap \\overline{R}")
An industry-leading company seeks a qualified candidate for a management position.
A management consultancy carries out an assessment center which concludes in making
a positive or negative recommendation for each candidate: From previous assessments they know that
of those candidates that are actually eligible for the position (event $E$) $r per * 100
\%$
get a positive recommendation (event $R$). However, out of those candidates that are not eligible
$r pnenr * 100
\%$ get a negative recommendation. Overall, they know that only
$r pe * 100
\%$ of all job applicants are actually eligible.
What is the corresponding fourfold table of the joint probabilities? (Specify all entries in percent.)
answerlist(paste("$P(", lab, ")$", sep = ""), markup = "markdown")
Using the information from the text, we can directly calculate the following joint probabilities:
$$
\begin{aligned}
P(E \cap R) & =
P(R | E) \cdot P(E) = r per
\cdot r pe
= r prob1
= r 100 * prob1
\%\
P(\overline{E} \cap \overline{R}) & =
P(\overline{R} | \overline{E}) \cdot P(\overline{E}) = r pnenr
\cdot r 1 - pe
= r prob4
= r 100 * prob4
\%.
\end{aligned}
$$
The remaining probabilities can then be found by calculating sums and differences in the fourfold table:
| | $R$ | $\overline{R}$ | sum |
|:-------------:|:------------------:|:------------------:|:------------------:|
|$E$ | r tab2[1, 1]
| r tab2[1, 2]
| r tab2[1, 3]
|
|$\overline{E}$ | r tab2[2, 1]
| r tab2[2, 2]
| r tab2[2, 3]
|
|sum | r tab2[3, 1]
| r tab2[3, 2]
| r tab2[3, 3]
|
answerlist(paste("$P(", lab, ") = ", format(sol), "\\%$", sep = ""), markup = "markdown")
extype: cloze
exsolution: r paste(sol, collapse = "|")
exclozetype: num|num|num|num
exname: fourfold
extol: 0.05
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