Match the concept to the correct answer:
\[
\begin{array}{|c|l|c|l|}
\hline
\textbf{P} & \text{Confounding} & \textbf{i)} & \text{We can draw clear causal conclusions from an experiment.} \\
\hline
\textbf{Q} & \text{High internal validity} & \textbf{ii)} & \text{Presence of an uncontrolled variable creates uncertainty as to} \\
& & & \text{whether the dependent variable was influenced by the independent variable.} \\
\hline
\textbf{R} & \text{High external validity} & \textbf{iv)} & \text{The results of a study generalize to other settings and populations.} \\
\hline
\textbf{S} & \text{Placebo effect} & \textbf{iii)} & \text{Participant improves because of the expectation of receiving a} \\
& & & \text{treatment, not because of the treatment itself.} \\
\hline
\end{array}
\]