\section{Discussion}
\label{sec:discussion}
In the following sections, we reiterate on our findings presented in the last
section and try to derive answers regarding our seven hypotheses and research
question \textit{``Does an adjusted actuation force per key have a positive
  impact on efficiency and overall satisfaction while using a mechanical
  keyboard?''}.

\subsection{Impact of Actuation Force on Typing Speed}
\label{sec:dis_speed}

Our main experiment yielded, that there are differences in typing speed for both
metrics related to transcribed text we measured―namely \glsfirst{WPM} and
\glsfirst{AdjWPM}. Especially the keyboard with the lowest uniform actuation
force of 35 g―\textit{Nyx}―performed worse than all other keyboards. In terms of
\gls{WPM}, \textit{Nyx (35 g)} was on average 4.1\% slower than \textit{Athena
  (80 g)} and \textit{Aphrodite (50 g)} and 4.8\% slower than the adjusted
keyboard \textit{Hera (35 - 60 g)}. Similarly, for \gls{AdjWPM}, \textit{Nyx}
was 4.3\% slower than \textit{Athena} and \textit{Aphrodite} and 4.9\% slower
than \textit{Hera}. The 4\% to 5\% difference in \gls{WPM} and \gls{AdjWPM} in
our sample account for approximately 2 words per minute. When extrapolated with
the mean daily keyboard usage of 6.69 hours reported by our participants, this
difference would be as big as 803 words, which when put into perspective, is
equivalent to roughly two full pages of only written content (11pt font
size). Although, this specific example would assume constant typing for 6.69
hours, it is still a useful estimate of the loss in productivity under normal
working conditions over the course of several days. These differences in
\gls{WPM} and \gls{AdjWPM} could be explained by the higher error rates and
thereby the loss of ``typing flow'' we discuss in the next section. \gls{KSPS}
reflects the raw input speed by including backspaces and previously deleted
characters. The reason we included \gls{KSPS} in our analysis was to reveal
possible differences in the physical speed participants type on a keyboard and
not to further asses speed in the sense of productivity. We could not find any
statistically significant differences in \gls{KSPS} but saw a trend, indicating
that subjects typed a bit slower (< 3\%) on \textit{Athena (80 g)} compared to
\textit{Aphrodite (50 g)} and \textit{Hera (35 - 60 g)}. With the differences in
metrics that are commonly used to measure typing speed more closely related to
productivity (\gls{WPM}, \gls{AdjWPM}) and the trends that indicate a slight
difference in operating speed, we can accept our hypothesis that solely a
difference in actuation force has an impact on typing speed.

\begin{phga_hyp}[\checkmark]
  Actuation force has an impact on typing speed (efficiency - speed).
\end{phga_hyp}

% During our telephone interviews 76\% of respondents would have preferred a
% keyboard with lighter actuation force.

% Our study tried to present the participant with a typing scenario that is as
% close to a typical text input situation as possible, by allowing but not
% enforcing the correction of erroneous input.

\subsection{Impact of Actuation Force on Error Rate}
\label{sec:dis_error}

As already briefly mentioned in Section \ref{sec:dis_speed}, measured error
rates like \glsfirst{UER}, \glsfirst{CER} and \glsfirst{TER} differed especially
between \textit{Nyx (35 g)} and the other test keyboards. The statistical
analyses further revealed, that \textit{Athena}, the keyboard with the highest
actuation force of 80 g, produced on average 1\% less \gls{TER} than
\textit{Hera (35 - 60 g)} and \textit{Aphrodite (50 g)} and 3\% less than
\textit{Nyx (35g)}. Furthermore, \textit{Hera} and \textit{Aphrodite} both had a
2\% lower \gls{TER} than \textit{Nyx}. Additionally to the quantitative results,
fourteen of the twenty-four participants also reported, that \textit{Nyx's}
light actuation force was the reason for many accidental key presses. It further
stood out, that as shown in Figure \ref{fig:max_opc_ter}, \textit{Athena} was
the most accurate keyboard for 58\% of participants and also more accurate than
keyboard \textit{Own} for eleven of the subjects. This concludes, that a higher
actuation force has a positive impact on error rate.

\begin{phga_hyp}[\checkmark]
  Higher key actuation force decreases typing errors compared to lower key
  actuation force (efficiency - error rate).
\end{phga_hyp}

\textbf{Impact of \gls{TER} on \gls{WPM}}

The higher error rates and the possibility to correct erroneous input could have
also been a factor that led to lower \textit{WPM}. To evaluate the likelihood of
this additional relation, we conducted a \gls{LRT} of fixed effects for our
linear mixed-effects model with two random effects (participant and first/second
typing test), fixed effect \gls{TER} and response variable \gls{WPM}. The
results of the \gls{LRT} ($\chi^2(1)$ = 110.44, p = 0.00000000000000022)
suggest, that the \gls{TER} indeed had an impact on \gls{WPM}. This could have
been, because every time an error was made, almost all participants decided to
correct it right away. With a higher error rate, this obviously leads to many
short interruptions and an increased number of characters that are not taken
into account when computing the \gls{WPM} metric.


\subsection{Impact of Actuation Force on Satisfaction}
\label{sec:dis_sati}

\subsection{Impact of Actuation Force on Muscle Activity}
\label{sec:dis_emg}

\subsection{Impact of an Adjusted Keyboard on Typing Speed, Error Rate and
  Satisfaction}
\label{sec:dis_hera}