# markmfredrickson/natural-experiments-in-genetics

RI basics, choices

 @@ -98,3 +98,43 @@ cat(tmp.str) These combine to form the \emph{Equal Environments Assumption (EEA)} \citep{Suhay:2009fy}. \end{frame} +\begin{frame}{Randomization Inference} + \begin{itemize} + \item Inference based only the random assignment; potential outcomes fixed + \item Intuition: If we remove the true'' effect, we can shuffle the MZ + and DZ labels and see no change. + \item Relatively few assumptions on the data; flexible enough to consider very complex + interactions between units, including interference \citep{Bowers:2012ys} + \end{itemize} +\end{frame} + +\begin{frame}{Randomization Inference Algorithm} + \begin{itemize} + \item Assignment Mechanism (e.g. simple random sample, coin flip) + \item Model of Effects ($Y_0 = Y_1 + \tau$, $Y_0 = \beta Y_1$, + interference) + \item Test Statistic (mean/median difference, rank sum, KS) + \item Algorithm: + \begin{enumerate} + \item Adjust data consistent with the model + \item Draw more random assignments + \item Compute test statistic + \end{enumerate} + \item Compute $p$-value of the model by comparing observed test statistic to the distribution + of test statistics + \item Implemented in development branch of \texttt{RItools} + \end{itemize} +\end{frame} + +\begin{frame}{Selecting Mechanisms, Models, and Statistics} + \begin{itemize} + \item Researcher has freedom (burden?) to select the assignment mechanism, + model of effects, and test statistic. + \item \textbf{Assignment mechanism:} Usually fixed at design time. In this case, + will assume a simple random sample within blocks defined by matching. + \item \textbf{Test Statistic:} Proper procedure uses power analysis. I just pick + mean difference. + \item \textbf{Model of effects:} I develop several models that conform to the + restrictions imposed by the ideology variable. + \end{itemize} +\end{frame}