9:59:59.000,9:59:59.000 - [Narrator] On his quest [br]to master econometrics, 9:59:59.000,9:59:59.000 Grasshopper Kamal has [br]made great progress 9:59:59.000,9:59:59.000 stretching his capabilities [br]and outsmarting his foes. 9:59:59.000,9:59:59.000 Alas, today he's despondent. 9:59:59.000,9:59:59.000 For one challenge remains unmet. 9:59:59.000,9:59:59.000 Kamal cannot yet decode [br]the scriptures of academic research, 9:59:59.000,9:59:59.000 journals like [br]"The American Economic Review" 9:59:59.000,9:59:59.000 and "Econometrica." 9:59:59.000,9:59:59.000 These seemed to him to be inscribed [br]in an obscure foreign tongue. 9:59:59.000,9:59:59.000 - [Kamal] Ugh, what the... ? 9:59:59.000,9:59:59.000 - [Narrator] These volumes are [br]opaque to novice, Kamal, 9:59:59.000,9:59:59.000 but can be deciphered with study. 9:59:59.000,9:59:59.000 Let us learn to read them together. 9:59:59.000,9:59:59.000 Let's dive into the West Point study, 9:59:59.000,9:59:59.000 published in the "Economics [br]of Education Review." 9:59:59.000,9:59:59.000 This paper reports [br]on a randomized evaluation 9:59:59.000,9:59:59.000 of student electronics use [br]in Economics 101 classrooms. 9:59:59.000,9:59:59.000 First, a quick review [br]of the research design. 9:59:59.000,9:59:59.000 - Okay. 9:59:59.000,9:59:59.000 - [Josh] 'Metrics masters [br]teaching at West Point, 9:59:59.000,9:59:59.000 the military college that trains [br]American Army officers 9:59:59.000,9:59:59.000 designed a randomized trial[br]to answer this question. 9:59:59.000,9:59:59.000 These masters randomly assigned[br]West Point cadets 9:59:59.000,9:59:59.000 into Economics classes[br]operating under different rules. 9:59:59.000,9:59:59.000 Unlike most American colleges, 9:59:59.000,9:59:59.000 the West Point default [br]is no electronics. 9:59:59.000,9:59:59.000 For purposes of this experiment,[br]some students were left 9:59:59.000,9:59:59.000 in such traditional [br]technology-free classes, 9:59:59.000,9:59:59.000 no lap tops, no tablets [br]and no phones! 9:59:59.000,9:59:59.000 [voice echoes] 9:59:59.000,9:59:59.000 This is the control group,[br]or baseline case. 9:59:59.000,9:59:59.000 Another group was allowed[br]to use electronics. 9:59:59.000,9:59:59.000 This is the treatment group,[br]subject to a changed environment. 9:59:59.000,9:59:59.000 The treatment in this case[br]is the unrestricted use 9:59:59.000,9:59:59.000 of laptops or tablets in class. 9:59:59.000,9:59:59.000 Every causal question [br]has a clear outcome, 9:59:59.000,9:59:59.000 the variables we hope to influence[br]defined in advance of the study. 9:59:59.000,9:59:59.000 The outcomes in the West Point[br]electronics study 9:59:59.000,9:59:59.000 are final exam scores. 9:59:59.000,9:59:59.000 The study seeks to answer[br]the following question, 9:59:59.000,9:59:59.000 what is the causal effect [br]of classroom electronics on learning 9:59:59.000,9:59:59.000 as measured by exam scores? 9:59:59.000,9:59:59.000 - Economics journal articles [br]usually begin with a table 9:59:59.000,9:59:59.000 of descriptive statistics,[br]giving key facts 9:59:59.000,9:59:59.000 about the study sample. 9:59:59.000,9:59:59.000 - Oh my gosh, I remember this table,[br]so confusing! 9:59:59.000,9:59:59.000 Columns 1 to 3 report mean,[br]or average, characteristics. 9:59:59.000,9:59:59.000 These give a sense [br]of who we're studying. 9:59:59.000,9:59:59.000 Let's start with column 1 [br]which describes covariates 9:59:59.000,9:59:59.000 in a control group. 9:59:59.000,9:59:59.000 Covariates are characteristics [br]of the control and treatment groups 9:59:59.000,9:59:59.000 measured before [br]the experiment begins. 9:59:59.000,9:59:59.000 For example, we see the control group[br]has an average age a bit over 20. 9:59:59.000,9:59:59.000 Many of these covariates [br]are dummy variables. 9:59:59.000,9:59:59.000 A dummy variable can only have [br]two values, a zero or a one. 9:59:59.000,9:59:59.000 For example, student gender[br]is captured by a dummy variable 9:59:59.000,9:59:59.000 that equals one for woman[br]and zero for man. 9:59:59.000,9:59:59.000 The mean of this variable [br]is the proportion female. 9:59:59.000,9:59:59.000 We also see that the control group [br]is 13% Hispanic 9:59:59.000,9:59:59.000 and 19% had prior military service. 9:59:59.000,9:59:59.000 The table notes are key. 9:59:59.000,9:59:59.000 Refer to these [br]as you scan the table. 9:59:59.000,9:59:59.000 These notes explain what's shown [br]in each column and panel. 9:59:59.000,9:59:59.000 The notes tell us, for example,[br]that standard deviations 9:59:59.000,9:59:59.000 are reported in brackets. 9:59:59.000,9:59:59.000 Standard deviations tell us how[br]spread out the data are. 9:59:59.000,9:59:59.000 For example, a standard deviation [br]of 0.52 tells us that most 9:59:59.000,9:59:59.000 of the control group's GPAs[br]fall between 2.35, 9:59:59.000,9:59:59.000 which is 0.52 below [br]the mean GPA of 2.87, 9:59:59.000,9:59:59.000 and 3.39, which is 0.52 above 2.87. 9:59:59.000,9:59:59.000 A lower standard deviation[br]would mean the GPAs were 9:59:59.000,9:59:59.000 more tightly clustered [br]around the mean. 9:59:59.000,9:59:59.000 - [Kamal] Yeah, but they're missing[br]from most of the variables. 9:59:59.000,9:59:59.000 - [Narrator] That's right. 9:59:59.000,9:59:59.000 Masters usually omit [br]standard deviations for dummies.