{ "cells": [ { "attachments": {}, "cell_type": "markdown", "metadata": {}, "source": [ "# Diagnostic checking\n", "*R.A. Collenteur, University of Graz, July 2020*.\n", "\n", "This notebook provides an overview of the different methods that are available for diagnostic checking of the models residuals in Pastas. Readers who want to get a quick overview of how to perform diagnostic checks on Pastas models are referred to section 2, while sections 3 to 6 are recommended for readers looking for in-depth discussions of the individual methods.\n", "\n", "1. [Introduction](#Introduction)\n", "2. [Diagnostic Checking in Pastas in Practice](#Diagnostics-checking-of-Pastas-models)\n", "2. [Checking for autocorrelation](#Checking-for-autocorrelation)\n", "3. [Checking for Homoscedasticity](#Checking-for-homoscedasticity)\n", "4. [Checking for Normality](#Checking-for-Normality)\n", "6. [References](#References)\n", "\n", "## Introduction\n", "Diagnostic checking is a common step in the time series modeling process, subjecting a calibrated model to various statistical tests to ensure that the model adequately describes the observed time series [(Hipel & McLeod, 2005)](#References). Diagnostics checks are performed on the residual or noise series of a model, depending on whether or not a noisemodel was applied in the modeling process. We will refer to the series that was minimized during parameter estimation as the \"residuals\". In practice in Pastas models, these can come from `ml.noise()` or `ml.residuals()`. Regardless of this, the diagnostics tests that may be performed remain the same.\n", "\n", "### Why to check: reasons to diagnose\n", "Before we start the discussion of what to check, let's briefly discuss why we would want to perform diagnostic checks at all. In general, diagnostic checks should be performed when you want to make inferences with a model, in particular when the estimated standard errors of the parameters are used to make such inferences. For example, if you want to draw the confidence interval of the estimated step response for a variable, you will use the standard errors of the parameters to do so. This assumes that the standard errors are estimated accurately, which may assumed if the minimized residual series agree with a number of assumptions on the characteristics of the model residuals.\n", "\n", "