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Table 1 Six possible complete matrices \( {\hat{\mathbbm{x}}}^{m=3} \) leading to the observed discovery matrix \( \mathbbm{d}=\left(\begin{array}{cc}1& 0\\ {}0& 1\end{array}\right) \)

From: Estimating the number of usability problems affecting medical devices: modelling the discovery matrix

Possibility 1

Possibility 2

Possibility 3

\( {\hat{\mathbbm{x}}}_1^{m=3}=\left(\begin{array}{ccc}1& 0& 0\\ {}0& 0& 1\end{array}\right) \)

\( {\hat{\mathbbm{x}}}_2^{m=3}=\left(\begin{array}{ccc}0& 1& 0\\ {}0& 0& 1\end{array}\right) \)

\( {\hat{\mathbbm{x}}}_3^{m=3}=\left(\begin{array}{ccc}1& 0& 0\\ {}0& 1& 0\end{array}\right) \)

Possibility 4

Possibility 5

Possibility 6

\( {\hat{\mathbbm{x}}}_4^{m=3}=\left(\begin{array}{ccc}0& 0& 1\\ {}1& 0& 0\end{array}\right) \)

\( {\hat{\mathbbm{x}}}_5^{m=3}=\left(\begin{array}{ccc}0& 0& 1\\ {}0& 1& 0\end{array}\right) \)

\( {\hat{\mathbbm{x}}}_6^{m=3}=\left(\begin{array}{ccc}0& 1& 0\\ {}1& 0& 0\end{array}\right) \)