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Name: \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Directions: MAKE SURE TO COPY YOUR ANSWERS TO A SEPARATE SHEET FOR SENDING
ME AN ELECTRONIC COPY LATER.

{\bf Important note:}  Remember that in problems calling for R code, you
are allowed to use any built-in R function, e.g. {\bf choose()}, {\bf
sum()}, {\bf integrate()}etc.  

{\bf 1.} (15) Consider the marble example, Section 11.5.  Find Var(Y $|$ B =
2).

{\bf 2.} (15) Suppose in Equation (8.22) I wish to form an 88\% confidence
interval, instead of a 95\% one.  Give an expression, which must involve
a call to one of the R functions we've used, to calculate the number
I'll use instead of 1.96.

{\bf 3.}  Consider the ``new, improved light bulbs'' example in Section
9.6.2.  {\Large \bf Note:  Each of the parts here is independent of the
others.}

\begin{itemize}

\item [(a)] (10) If we wished to have significance level $\alpha = 0.10$,
sampling 50 bulbs, what should be our threshhold for rejection, like
the w in the example?

\item [(b)] (15) Suppose we have 15 people test batches of 10 light bulbs,
each performing a significance test as in the example.  Suppose also
that actually $H_0$ is true.  Find the probability that at least 3 of
the people reject $H_0$.

\item [(c)] (15) Suppose it turns out that $\overline{X} = 1624.2$.  Find
the p-value.

\end{itemize}

{\bf 4.}  In the baseball data, Section 11.7, I wanted to run separate
regression analyses for catchers and starting pitchers.  

\begin{itemize}

\item [(a)] (15) I extracted the two subsets of my original data frame
{\bf players}, naming them {\bf catch} and {\bf pitch}.  Give one line
of R code that creates {\bf catch}.

\item [(b)] (15) I ran regressions of weight on height in the two groups,
with these results:

\begin{Verbatim}[fontsize=\relsize{-2}]
> summary(lm(catch$Weight ~ catch$Height))

Call:
lm(formula = catch$Weight ~ catch$Height)

Residuals:
    Min      1Q  Median      3Q     Max 
-31.505  -7.603  -1.603   8.495  31.789 

Coefficients:
             Estimate Std. Error t value Pr(>|t|)    
(Intercept)  -79.4301    67.9087   -1.17    0.246    
catch$Height   3.9019     0.9335    4.18 7.91e-05 ***

> summary(lm(pitch$Weight ~ pitch$Height))

Call:
lm(formula = pitch$Weight ~ pitch$Height)

Residuals:
    Min      1Q  Median      3Q     Max 
-45.236 -15.236  -0.193  12.527  65.883 

Coefficients:
              Estimate Std. Error t value Pr(>|t|)    
(Intercept)  -126.6988    44.4338  -2.851  0.00477 ** 
pitch$Height    4.4407     0.5943   7.472 1.89e-12 ***
---
\end{Verbatim}

Find an approximate 95\% confidence interval for the difference
(catchers minus pitchers) between the slopes for the Height variables
for the two groups.

\end{itemize}

\onecolumn

\newpage

{\bf Solutions:}

{\bf 1.}  

$$
0^2 \cdot 0.036/0.090 +
1^2 \cdot 0.048/0.090 +
2^2 \cdot 0.006/0.090
- 0.667^2
$$

{\bf 2.}

\begin{lstlisting}
-qnorm(0.06)
\end{lstlisting}

{\bf 3.a}

\begin{lstlisting}
qgamma(0.90,50,0.001) / 50
\end{lstlisting}

{\bf 3.b}

\begin{lstlisting}
1 - pbinom(2,15,0.05)
\end{lstlisting}

{\bf 3.c}

\begin{lstlisting}
1 - pgamma(16242,10,0.001)
\end{lstlisting}

{\bf 4.a}

\begin{lstlisting}
catch <- subset(players,Position == "Catcher")
\end{lstlisting}

or

\begin{lstlisting}
catch <- players[players$Position == "Catcher",]
\end{lstlisting}

{\bf 4.b}

$$
(3.9019 - 4.4407) \pm 1.96 \sqrt{0.9335^2 + 0.5943^2}
$$

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