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\section{Discussion}
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\label{sec:label}
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\label{sec:discussion}
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In the following sections, we reiterate on our findings presented in the last
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section and try to derive answers regarding our seven hypotheses and research
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question \textit{``Does an adjusted actuation force per key have a positive
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impact on efficiency and overall satisfaction while using a mechanical
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keyboard?''}.
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\subsection{Impact of Actuation Force on Typing Speed}
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\label{sec:dis_speed}
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Our main experiment yielded, that there are differences in typing speed for both
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metrics related to transcribed text we measured―namely \glsfirst{WPM} and
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\glsfirst{AdjWPM}. Especially the keyboard with the lowest uniform actuation
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force of 35 g―\textit{Nyx}―performed worse than all other keyboards. In terms of
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\gls{WPM}, \textit{Nyx (35 g)} was on average 4.1\% slower than \textit{Athena
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(80 g)} and \textit{Aphrodite (50 g)} and 4.8\% slower than the adjusted
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keyboard \textit{Hera (35 - 60 g)}. Similarly, for \gls{AdjWPM}, \textit{Nyx}
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was 4.3\% slower than \textit{Athena} and \textit{Aphrodite} and 4.9\% slower
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than \textit{Hera}. The 4\% to 5\% difference in \gls{WPM} and \gls{AdjWPM} in
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our sample account for approximately 2 words per minute. When extrapolated with
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the mean daily keyboard usage of 6.69 hours reported by our participants, this
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difference would be as big as 803 words, which when put into perspective, is
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equivalent to roughly two full pages of only written content (11pt font
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size). Although, this specific example would assume constant typing for 6.69
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hours, it is still a useful estimate of the loss in productivity under normal
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working conditions over the course of several days. These differences in
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\gls{WPM} and \gls{AdjWPM} could be explained by the higher error rates and
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thereby the loss of ``typing flow'' we discuss in the next section. \gls{KSPS}
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reflects the raw input speed by including backspaces and previously deleted
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characters. The reason we included \gls{KSPS} in our analysis was to reveal
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possible differences in the physical speed participants type on a keyboard and
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not to further asses speed in the sense of productivity. We could not find any
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statistically significant differences in \gls{KSPS} but saw a trend, indicating
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that subjects typed a bit slower (< 3\%) on \textit{Athena (80 g)} compared to
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\textit{Aphrodite (50 g)} and \textit{Hera (35 - 60 g)}. With the differences in
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metrics that are commonly used to measure typing speed more closely related to
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productivity (\gls{WPM}, \gls{AdjWPM}) and the trends that indicate a slight
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difference in operating speed, we can accept our hypothesis that solely a
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difference in actuation force has an impact on typing speed.
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\begin{phga_hyp}[\checkmark]
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Actuation force has an impact on typing speed (efficiency - speed).
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\end{phga_hyp}
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% During our telephone interviews 76\% of respondents would have preferred a
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% keyboard with lighter actuation force.
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% Our study tried to present the participant with a typing scenario that is as
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% close to a typical text input situation as possible, by allowing but not
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% enforcing the correction of erroneous input.
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\subsection{Impact of Actuation Force on Error Rate}
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\label{sec:dis_error}
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As already briefly mentioned in Section \ref{sec:dis_speed}, measured error
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rates like \glsfirst{UER}, \glsfirst{CER} and \glsfirst{TER} differed especially
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between \textit{Nyx (35 g)} and the other test keyboards. The statistical
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analyses further revealed, that \textit{Athena}, the keyboard with the highest
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actuation force of 80 g, produced on average 1\% less \gls{TER} than
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\textit{Hera (35 - 60 g)} and \textit{Aphrodite (50 g)} and 3\% less than
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\textit{Nyx (35g)}. Furthermore, \textit{Hera} and \textit{Aphrodite} both had a
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2\% lower \gls{TER} than \textit{Nyx}. Additionally to the quantitative results,
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fourteen of the twenty-four participants also reported, that \textit{Nyx's}
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light actuation force was the reason for many accidental key presses. It further
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stood out, that as shown in Figure \ref{fig:max_opc_ter}, \textit{Athena} was
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the most accurate keyboard for 58\% of participants and also more accurate than
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keyboard \textit{Own} for eleven of the subjects. This concludes, that a higher
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actuation force has a positive impact on error rate.
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\begin{phga_hyp}[\checkmark]
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Higher key actuation force decreases typing errors compared to lower key
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actuation force (efficiency - error rate).
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\end{phga_hyp}
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\textbf{Impact of \gls{TER} on \gls{WPM}}
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The higher error rates and the possibility to correct erroneous input could have
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also been a factor that led to lower \textit{WPM}. To evaluate the likelihood of
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this additional relation, we conducted a \gls{LRT} of fixed effects for our
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linear mixed-effects model with two random effects (participant and first/second
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typing test), fixed effect \gls{TER} and response variable \gls{WPM}. The
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results of the \gls{LRT} ($\chi^2(1)$ = 110.44, p = 0.00000000000000022)
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suggest, that the \gls{TER} indeed had an impact on \gls{WPM}. This could have
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been, because every time an error was made, almost all participants decided to
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correct it right away. With a higher error rate, this obviously leads to many
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short interruptions and an increased number of characters that are not taken
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into account when computing the \gls{WPM} metric.
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\subsection{Impact of Actuation Force on Satisfaction}
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\label{sec:dis_sati}
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\subsection{Impact of Actuation Force on Muscle Activity}
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\label{sec:dis_emg}
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\subsection{Impact of an Adjusted Keyboard on Typing Speed, Error Rate and
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Satisfaction}
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\label{sec:dis_hera}
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