A Researcher Had a Categorical Variable That They Wanted to Include

question 7

Multiple Choice

A researcher had a categorical variable that they wanted to include as a predictor in a regression equation. The researcher was trying to predict the success of a back pain intervention, and the categorical variable was the duration of the back pain prior to treatment, with 4 categories: less than 6 months, 6-12 months, 1-2 years, more than 2 years. They needed to code these variables into dummy variables for the regression using less than 6 months as their control category. Which of the following represents the correct coding scheme?

• A) \[\begin{array} { | l | l | r | r | r | }
• \hline\quad\quad\quad\quad & \quad\quad\begin{array} { c }
• \\
• \\
• \\
• \text { Duration of Pain } \\
• \end{array} & \begin{array} { c }
• \text { Dummy 1 } \\
• \text { (Under 6 } \\
• \text { Months vs } \\
• \text { 6-12 Months) }
• \end{array} & \begin{array} { c }
• \text { Dummy 2 } \\
• \text { (Under 6 } \\
• \text { Months vs } \\
• 1 - 2 \text { Years) }
• \end{array} & \begin{array} { c }
• \text { Dummy 3 } \\
• \text { (Under 6 } \\
• \text { Months vs } \\
• \text { Over 2 Years) }
• \end{array} \\
• \hline
• & \text { Under 6 Months } & 1 & 1 & 1 \\
• & \text { 6-12 Months } &1 & 0 & 0\\
• & 1 - 2 \text { Years }& 0 & 1 & 0 \\
• &\text { More Than 2 Years }& 0 & 0 & 1\\
• \hline
• \end{array}\]
• B) \[\begin{array} { | l | l | r | r | r | }
• \hline\quad\quad\quad\quad & \quad\quad\begin{array} { c }
• \\
• \\
• \\
• \text { Duration of Pain } \\
• \end{array} & \begin{array} { c }
• \text { Dummy 1 } \\
• \text { (Under 6 } \\
• \text { Months vs } \\
• \text { 6-12 Months) }
• \end{array} & \begin{array} { c }
• \text { Dummy 2 } \\
• \text { (Under 6 } \\
• \text { Months vs } \\
• 1 - 2 \text { Years) }
• \end{array} & \begin{array} { c }
• \text { Dummy 3 } \\
• \text { (Under 6 } \\
• \text { Months vs } \\
• \text { Over 2 Years) }
• \end{array} \\
• \hline
• & \text { Under 6 Months } & 0 & 0 & 0 \\
• & \text { 6-12 Months } &1 & 0 & 0\\
• & 1 - 2 \text { Years }& 0 & 1 & 0 \\
• &\text { More Than 2 Years }& 0 & 0 & 1\\
• \hline
• \end{array}\]
• C) \[\begin{array} { | l | l | r | r | r | }
• \hline\quad\quad\quad\quad & \quad\quad\begin{array} { c }
• \\
• \\
• \\
• \text { Duration of Pain } \\
• \end{array} & \begin{array} { c }
• \text { Dummy 1 } \\
• \text { (Under 6 } \\
• \text { Months vs } \\
• \text { 6-12 Months) }
• \end{array} & \begin{array} { c }
• \text { Dummy 2 } \\
• \text { (Under 6 } \\
• \text { Months vs } \\
• 1 - 2 \text { Years) }
• \end{array} & \begin{array} { c }
• \text { Dummy 3 } \\
• \text { (Under 6 } \\
• \text { Months vs } \\
• \text { Over 2 Years) }
• \end{array} \\
• \hline
• & \text { Under 6 Months } & 0 & 0 & 0 \\
• & \text { 6-12 Months } &0 &1 & 1\\
• & 1 - 2 \text { Years }& 1 & 0 & 1 \\
• &\text { More Than 2 Years }& 1 &1&0\\
• \hline
• \end{array}\]
• D) \[\begin{array} { | l | l | r | r | r | }
• \hline\quad\quad\quad\quad & \quad\quad\begin{array} { c }
• \\
• \\
• \\
• \text { Duration of Pain } \\
• \end{array} & \begin{array} { c }
• \text { Dummy 1 } \\
• \text { (Under 6 } \\
• \text { Months vs } \\
• \text { 6-12 Months) }
• \end{array} & \begin{array} { c }
• \text { Dummy 2 } \\
• \text { (Under 6 } \\
• \text { Months vs } \\
• 1 - 2 \text { Years) }
• \end{array} & \begin{array} { c }
• \text { Dummy 3 } \\
• \text { (Under 6 } \\
• \text { Months vs } \\
• \text { Over 2 Years) }
• \end{array} \\
• \hline
• & \text { Under 6 Months } & 0 & 0 & 0 \\
• & \text { 6-12 Months } &0 &1 & 1\\
• & 1 - 2 \text { Years }& 1 & 0 & 1 \\
• &\text { More Than 2 Years }& 1 &1&0\\
• \hline
• \end{array}\]

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