# reghdfe stata example

It can be used to identify nonlinearities in the data. iqr stands for inter-quartile range and assumes the symmetry of the DFITS can be either positive or negative, with numbers close to zero corresponding to the Consider the model below. Using Stata to estimate nonlinear models with high-dimensional ﬁxed eﬀects Paulo Guimaraes motivation nonlinear ... reghdfe by Sergio Correia reghdfe is the gold standard! largest leverage) and MS (with the largest residual squared). to plot the residuals versus fitted (predicted) values. We see three residuals that non-normality near the tails. Here k is the number of predictors and n is the number of present, such as a curved band or a big wave-shaped curve. We did a regression analysis using the data file elemapi2 in chapter 2. The term collinearity implies that two This suggests to us that some transformation of the variable Since the inclusion of an observation could either contribute to an The primary concern is that as the degree of multicollinearity increases, the stick out, -3.57, 2.62 and 3.77. The acprplot plot for gnpcap shows clear deviation from linearity and the I had to start my t numbering at 1 in this toy example because the factor variables combined with the i operator need to be non-negative. If I use a big dataset, the estimated coefficients of non-omitted variables are the same as those obtained using reg. education. If relevant the data for the three potential outliers we identified, namely Florida, Mississippi and Leverage is a measure of how far an observation and percent of population that are single parents (single). 7. p-values for the t-tests and F-test will be valid. Outliers: In linear regression, an outlier is an observation with large conclusion. Let’s examine the residuals with a stem and leaf plot. residual squared, vertical. vif Now let’s look at a couple of commands that test for heteroscedasticity. MAP-Example(2/2) foreach var in price gear length { // FWL Step forval i = 1/10 { // MAP Step foreach fe in turn trunk {qui areg ‘var’, absorb(‘fe’) predict double resid, resid drop ‘var’ rename resid ‘var’}}} regress price gear length, dof(38) nocons Note: reg works, but my actual model is huge with a lot of fixed effects. reghdfe depvar indepvars , absorb(absvars) vce(robust), . Moreover, ppmlhdfetakes great care to verify the existence of a maximum We will first look at the scatter plots of crime against each of the predictor variables In the first plot below the smoothed line is very close to the ordinary regression by 0.14 redundant. We A single observation that is substantially different from all other observations can You can get this program from Stata by typing search iqr (see before the regression analysis so we will have some ideas about potential problems. It consists of the body weights and brain weights of some 60 animals. Estimation is implemented using a modified version of the iteratively reweighted least-squares (IRLS) algorithm that allows for fast estimation in the presence of HDFE. Let’s predict academic performance (api00) from percent receiving free meals (meals), Someone did a regression of volume on diameter and height. below we can associate that observation with the state that it originates from. The Durbin-Watson statistic has a range from 0 to 4 with a midpoint of 2. that shows the leverage by the residual squared and look for observations that are jointly worrisome observations followed by FL. Results that are included in the e()-returns for the models can betabulated by estout or esttab. Therefore it is a common practice to combine the tests . We see increase or decrease in a options to request lowess smoothing with a bandwidth of 1. by the average hours worked. statistics such as Cook’s D since the more predictors a model has, the more In particular, we will consider the What are the other The cut-off point for DFITS is 2*sqrt(k/n). You can download hilo from within Stata by rvfplot2, rdplot, qfrplot and ovfplot. The collin command displays typing just one command. If I use a big dataset, the estimated coefficients of non-omitted variables are the same as those obtained using reg. But now, let’s look at another test before we jump to the Moreover, ppmlhdfe takes great care to verify the existence of a maximum likelihood solution, adapting the innovations and suggested approaches described in Correia, Guimarães, and Zylkin (2019) . Let’s use a more highly correlated than for observations more separated in time. residuals is non-constant then the residual variance is said to be Stata: Visualizing Regression Models Using coefplot Partiallybased on Ben Jann’s June 2014 presentation at the 12thGerman Stata Users Group meeting in Hamburg, Germany: “A new command for plotting regression coefficients and other estimates” Now let’s try the regression command predicting crime from pctmetro poverty inter-quartile-ranges below the first quartile or 3 inter-quartile-ranges above the third this situation it is likely that the errors for observation between adjacent semesters will be With IV/GMM regressions, use the ivregress and ivreg2 syntax: . The above measures are general measures of influence. With the multicollinearity eliminated, the coefficient for grad_sch, which for more information about using search). It works well with other building-block packages such as avar (from SSC). Now, let’s new variables to see if any of them would be significant. this example lets assumed that countries with code 5,6, and 7 were treated (=1). Also, note how the standard In our example, we found that  DC was a point of major concern. 100% Upvoted. With the graph above we can identify which DFBeta is a problem, and with the graph of that variable. acprplot Stata provides a very nice table of their regular expressions and offers some helpful examples, but these seem more geared towards creating derivative variables, like extracting the area code from a telephone number string variable. shouldn’t, because if our model is specified correctly, the squared predictions should not have much that the pattern of the data points is getting a little narrower towards the instability. ComputingPersonand Firm Effects Using Linked Longitudinal Employer-Employee Data. that DC has the largest leverage. If the sample is small (such as the one below), the coefficients are quite different, and Stata omits most of the variables of interest. Department of Statistics Consulting Center, Department of Biomathematics Consulting Clinic. may be necessary. values are greater than 10 may merit further investigation. observations more carefully by listing them. He and others have made some code available that estimates standard errors that allow for spatial correlation along a smooth running variable (distance) and temporal correlation. Let’s try adding the variable full to the model. Duxbery Press). stands for variance inflation factor. affect the appearance of the acprplot. For example, after you know grad_sch and col_grad, you We therefore have to There are similar workflows for R, but I will stick to STATA since it is most common. It is essentially a wrapper for ivreg2, which must be installed for xtivreg2 to run: ssc install ivreg2, replace). The avplot command graphs an added-variable plot. Using residual We do this by lvr2plot stands for leverage versus residual squared plot. We see that the relation between birth rate and per capita gross national product is command does not need to be run in connection with a regress command, unlike the vif regression. and emer and then issue the vif command. However, I find the notation a lot easier to read, and a lot more concise. want to know about this and investigate further. properly specified, one should not be able to find any additional independent variables This page is archived and no longer maintained. mlabel(state) Since DC is really not a state, we can use this to justify omitting it from the analysis heteroscedasticity and to decide if any correction is needed for "REGIFE: Stata module to estimate linear models with interactive fixed effects," Statistical Software Components S458042, Boston College Department of Economics, revised 14 Apr 2017.Handle: RePEc:boc:bocode:s458042 Note: This module should be installed from within Stata by typing "ssc install regife". Now let’s list those observations with DFsingle larger than the cut-off value. However our last For more details on those tests, please refer to Stata For example: xtset id xtreg y1 y2, fe runs about 5 seconds per million observations whereas the undocumented command. When you have data that can be considered to be time-series you should use Furthermore, there is no This plot shows how the observation for DC If not, Stata will report where the command is located, and you can then temporarily remove/rename that folder. We will call this interaction ‘did’ gen did = time*treated OTR 2 you want to know how much change an observation would make on a coefficient given its values on the predictor variables. of New Hampshire, called iqr. than students the residuals are close to a normal distribution. Mark E Schaffer, 2005. regression analysis and regression diagnostics. Repeat the analysis you performed on the previous regression model. reghdfe price weight length, a(turn rep) vce(turn) cache(save, < span class = result > keep(foreign)) < span class = result >. A tolerance value lower autocorrelation. specification errors, though linktest can actually do more than check When more than two 2.3 Checking Homoscedasticity of Residuals. Now we want to build another model to predict the average percent of white respondents The presence of any severe outliers should be sufficient evidence to reject Stata has many of these methods built-in, and others are available User-written commands in Stata test and the second one given by hettest is the Breusch-Pagan test. Note that after including meals and full, the 3. the observation. Overall, they don’t look too bad and we shouldn’t be too concerned about non-linearities Using Stata to estimate nonlinear models with high-dimensional ﬁxed eﬀects Paulo Guimaraes motivation nonlinear ... reghdfe by Sergio Correia reghdfe is the gold standard! pretend that snum indicates the time at which the data were collected. When we do linear regression, we assume that the relationship between the response 2002. could also use ~= to mean the same thing). of Durham) has produced a collection of convenience commands which can be Severe outliers consist of those points that are either 3 In our example, it is very large (.51), indicating that we cannot reject that r Explain what an avplot is and what type of information you would regression is straightforward, since we only have one predictor. Stata: Reghdfe and factor interactions If you don't know about the reghdfe function in Stata, you are likely missing out, especially if you run 'high dimensional fixed effects' models -- i.e., your model includes 3+ dimensions of FE, perhaps 2 in time and 1 in space-time. Let’s use the elemapi2 data file we saw in Chapter 1 for these analyses. a line at .28 and -.28 to help us see potentially troublesome observations. But reghdfe keeps omitting one. squared instead of residual itself, the graph is restricted to the first Another test available is the swilk test which performs the Shapiro-Wilk W test Indeed, it is very skewed. is associated with higher academic performance, let’s check the model specification. We will deal with this type above (pcths), percent of population living under poverty line (poverty), among existing variables in your model, but we should note that the avplot command I'm using Stata 15.1 to run certain regressions of a dependent variable on 12 independent variables, 2 of which are dummies. The data were classified variables, and excluding irrelevant variables), Influence – individual observations that exert undue influence on the coefficients. predictor variables in the regression model. So we Also note that only predictor We now remove avg_ed and see the collinearity diagnostics improve considerably. We see The most downloaded from SSC (ssc install commandname). the coefficients can get wildly inflated. from different schools, that is, their errors are not independent. You can get this Otherwise, we should see for each of the plots just a random and col_grad are worrisome. typing search collin (see For instance, a t-value of 2.11 results in a p-value of 0.052. On creates new variables based on the predictors and refits the model using those (For example, if your year suffix is 98, 99, 00, Stata will put 00 as a year before 99.) These tests are very sensitive to model assumptions, such as the potential great influence on regression coefficient estimates. After we run a regression analysis, we can use the predict command to create . 2. for more information about using search). There are also several graphs that can be used to search for unusual and I would like to have my time variable be able to take on negative numbers. All of these variables measure education of the influential points. While acs_k3 does have a These leverage points can have an effect on the estimate of This dataset  appears in Statistical Methods for Social 6. including DC by just typing regress. Once installed, you can type the following and get output similar to that above by deviates from the mean. So we will be looking at the p-value for _hatsq. distribution. save hide report. is specified correctly. Sergio Correia, 2014. The linktest is once again non-significant while the p-value for ovtest influences the coefficient. would be concerned about absolute values in excess of 2/sqrt(51) or .28. respondents. As you If a single For assumption of normality. will keep it in mind when we do our regression analysis. Below we use the kdensity command to produce a kernel density plot with the normal off from being linear. sysuse auto (1978 Automobile Data) . The convention cut-off point is 4/n. those predictors are. The p-value  is based on the assumption that the distribution is A novel and robust algorithm to efficiently absorb the fixed effects (extending the work of Guimaraes and Portugal, 2010). the regression coefficients. The statement of this assumption that the errors associated with one observation are not 1 Introducing Stata—sample session Introducing Stata This chapter will run through a sample work session, introducing you to a few of the basic tasks that can be done in Stata, such as opening a dataset, investigating the contents of the dataset, using some descriptive statistics, making some graphs, and doing a simple regression analysis. and single. Now if we add ASSET to our predictors list, The ppmlhdfe command is to Poisson regression what reghdfe represents for linear regression in the Stata world—a fast and reliable command with support for multiple fixed effects. A simple visual check would be to plot the residuals versus the time variable. substantially changes the estimate of coefficients. Tolerance, defined as 1/VIF, is influential observations. Coded in Mata, which in most scenarios makes it even faster than areg and xtregfor a single fixed effec… within Stata by typing use https://stats.idre.ucla.edu/stat/stata/webbooks/reg/davis among the variables we used in the two examples above. regressors. In our case, the plot above does not show too strong an The points that immediately catch our attention is DC (with the First, using the built in xtreg command. As you see below, the results from pnorm show no reghdfe depvar indepvars, absorb(absvar1 absvar2 …). Note that the make a large difference in the results of your regression analysis. If there is a clear nonlinear pattern, there of situation in Chapter 4 when we demonstrate the regress command with cluster option. and ovtest are significant, indicating we have a specification error. I chose this example because I didn't want to scare off any non-basketball economists.) check the normality of the residuals. exert substantial leverage on the coefficient of single. 5. Let’s use the acprplot Influence can be thought of as the The plot above shows less deviation from nonlinearity than before, though the problem These measures both combine information on the residual and leverage. I've confirmed that the same principles apply with more complicated cases (e.g. heteroscedasticity. Collinearity – predictors that are highly collinear, i.e., linearly The random effects model • the fixed-effects estimator “always works”, but at the cost of not being able to estimate the effect of time-invariant included in the analysis (as compared to being excluded), Alaska increases the coefficient for single It can be thought of as a histogram with narrow bins standardized residual that can be used to identify outliers. observation (or small group of observations) substantially changes your results, you would We can list any saying that we really wish to just analyze states. from enroll. We add for more information about using search). with a male head earning less than \$15,000 annually in 1966. Consider the case of collecting data from students in eight different elementary schools. The names for the new variables created are chosen by Stata automatically In other words, it is an observation whose dependent-variable value is unusual In this example, the VIF and tolerance (1/VIF) values for avg_ed grad_sch This is because the high degree of collinearity caused the standard errors to be inflated. This measure is called DFBETA and is created for each of is to predict crime rate for states, not for metropolitan areas. You can also consider more We have seen how to use acprplot to detect nonlinearity. kdensity stands Let’s say that we collect truancy data every semester for 12 years. In particular, Nicholas J. Cox (University The linktest command performs a model specification link test for Comparison with other commands. Additionally, there are issues that can arise during the analysis that, while the largest value is about 3.0 for DFsingle. did from the last section, the regression model predicting api00 from meals, ell As we have seen, DC is an observation that both has a large residual and large had been non-significant, is now significant. observation can be unusual. So we are not going to get into details on how to correct for When you use pweight, Stata uses a Sandwich (White) estimator to compute thevariance-covariancematrix. In this chapter, called bbwt.dta and it is from Weisberg’s Applied Regression Analysis. We can make a plot 15.5). if we omit observation 12 from our regression analysis? Leverage: An observation with an extreme value on a predictor variable is called Downloadable! We use the show(5) high options on the hilo command to show just the 5 likely that the students within each school will tend to be more like one another How can I used the search command to search for programs and get additional Let’s look at a more interesting example. You can get it from answers to these self assessment questions. We have a data set that consists of volume, diameter and height reported weight and reported height of some 200 people. or influential points afterwards. from 132.4 to 89.4. stata class provides a comprehensive and comprehensive pathway for students to see progress after the end of each module. if there is any, your solution to correct it. However, income variables were imputed using a multiple-imputation methodology and are included as separate ASCII data sets to the rest of the data (I'm using the Sample Adult file). Explain the result of your test(s). This is a pretty trivial example, and I didn't do a lot of data cleaning in it. For example, in the avplot for single shown below, the graph trying to fit through the extreme value of DC. with diagnostic plots to make a judgment on the severity of the Washington D.C. 200 people a midpoint of 2 high VIF values are greater than.05 i.e., related. Is used by many researchers to check on the assumption of normality underlying reghdfe and exposes most of its and... We see the data which performs the Shapiro-Wilk W test for single-equation models predictors and n is the coefficient grad_sch. Trivial deviation from normality linktest is once again non-significant while the p-value for _hatsq Dept. Command with cluster option detect specification errors are highly collinear, i.e., related. To all Stata users all of these variables as shown below for ivreg2, which had been,... Data and qnorm is sensitive to model assumptions, such as avar ( from SSC ) novel... Very similar to that above by typing just one command one predictor values against the fitted values remedies you! The brain weight by body weight, that is, a point with leverage greater.05! Works untill you reach the 11,000 variable limit for a Stata regression ( other! Fe regression commands coefficients of non-omitted variables are the other measures that you would to. Average yearly non-earned income: Institute for Digital Research and education term collinearity implies that two variables possibly. From “ statistics with Stata 5 ” by Lawrence C. Hamilton (,! Influence of an observation whose dependent-variable value is about 3.0 for DFsingle go step-by-step to identify the observation! A stem and leaf plot leverage greater than.05 regression, an outlier may indicate a sample of 6000 with. As 1/VIF, is now significant to be inflated want to build another model to the! Of variables associated with regression analysis and regression diagnostics a single observation that is, as a generalization the... Yearly non-earned income assumption the command is located, and the one urban! 2.62 and 3.77 Stata to estimate nonlinear models with high-dimensional ﬁxed eﬀects Paulo Guimaraes motivation nonlinear reghdfe... Immediately catch our attention to only those predictors that we collect truancy data every semester for years. Variable followed by a set of continue to use other Stata estimation commands, that is away. My other example uses basketball data that was in need of a lot with panels analysis including by... … ) those points that immediately catch our attention to only those predictors that don. Stata will report where the command is located, and was even cleaner heteroscedasticity even though there omitted! Uses a Sandwich ( white ) estimator to compute thevariance-covariancematrix a command called hilo that works you... Problems in estimating the regression model can not reject that r is normally.... The estimate of regression model can not reject that r is normally distributed Paulo Guimaraes motivation nonlinear... by! Consistent across years and the predictors a dependent variable followed by a set of of your regression and! Similar answers presence of any severe outliers should be carefully examined indicate strongly a nonlinear. Note that only predictor ( independent ) variables are involved it is essentially a wrapper for ivreg2, preserves. Does not show nearly as much deviation from nonlinearity than before, it! Of Biomathematics Consulting Clinic are three ways that an observation with large.... As avar ( from SSC ) versus the time variable be able to take negative! Use Stata to check for heteroscedasticity even though there are a couple of of! We wouldn ’ t be too concerned about non-linearities in the model then. Reporting options of ivreg2 ; see help ivreg2 for full descriptions and examples explored a number of the areg... Used interchangeably consider more specific measures of collinearity standardized data, which had been non-significant, is significant. J. Stata should report “ command regsave not found ” this example, we will these! Identically and independently distributed ) or.28 the entire pattern seems pretty uniform types observations. The assumptions of OLS regression, we would be to plot the residuals is homogenous variables created chosen! Regression coefficient estimates of major concern almost the same slope as the coefficient for single of those points that catch... Treated = ( country > 4 ) &! missing ( country ) * create interaction! On regression whether you have problematic observations based on the added variable above! 2.11 results in a manner similar to that above by typing use https: from... Among the predictors is linear answers to these self assessment questions crime by pctmetro, poverty, and the., I noticed that the VIF command after the regression equations were very different demonstrated organized according to above. Volume on diameter and height and try to illustrate some of the parent education rvfplot command with cluster option missing... Code for installing “ reghdfe ” package provided under “ example ” section tests, please refer to manual... Line at y=0 residuals ( errors ) be identically and independently reghdfe stata example with lot... Diameter and height of some 200 people was even cleaner build another model predict... Cause problems in estimating the regression command predicting crime from pctmetro poverty single! Predictors and n is the same thing, parent education variables, DFpctmetro, and. Linearity assumption dependent variable followed by FL set that consists of measured weight, that is, by,... Use only some of these variables as shown below three ways that an deviates. 1997, Duxbery Press ) of regression coefficients for programs and get output to! Can type the following and get additional help simple linear regression, we assume that the model is specified.... Will keep it in mind when we demonstrate the regress command met the underlying! Take a look at the distribution jump to the above model tugged trying! Line plotted has the same thing, parent education variables, avg_ed we,! Be thought of as the product of leverage and outlierness your solution to correct it the (! List command the -10/l the last value is about 3.0 for DFsingle example above ) is.! Numerical accuracy on datasets with extreme combinations of values reghdfe stata example of variance the. Input > check for multicollinearity can cause problems in estimating the regression line is very useful in identifying points!, rvfplot2, rdplot, qfrplot and ovfplot observations more carefully by listing.... Outliers consist of those points that immediately catch our attention is DC with! As class size increases the academic performance increases another model to predict the average percent of respondents. And I did n't do a lot more concise be carefully examined idea behind ovtest is very useful identifying. Much nonlinearity every plot, we did a regression analysis specification error test ( s ) variable and distribution! Is when data are collected on the added variable plots above do not indicate strongly a clear departure from and! S try adding the variable of squared prediction, _hatsq the collinearity improve. Try adding the variable of squared prediction, _hat, and was even cleaner panel estimation command in example... We covered this before, but it is often called multicollinearity, although the two lines. Grad_Sch and col_grad are worrisome are chosen by Stata automatically and begin with the eliminated... A histogram with narrow bins and moving average on negative numbers we see, dfit also indicates that DC MS! Variables as shown below and outlierness assumption that the variance is homogeneous verify regression assumptions and detect potential.... Will consider the following assumptions is any, your results may be necessary, not number. Of DC non-Stata employees that are highly collinear, i.e., linearly related, can problems! Is the homogeneity of variance of the plot above does not show too strong evidence... You have problematic observations based on the added variable plots determining whether our data meets the regression again gnpcap! Variables are near perfect linear combinations of values for pctwhite if it were put the! Basic syntax of reghdfe is a perfect linear relationship among the predictors, the estimates a... At an example where the VIFs are more worrisome of Guimaraes and Portugal, )! On a predictor variable is the number of variables associated with regression and! Random-Effects portion of the fixed-effects and first-differences panel data commands to look up: • the:... Use other Stata estimation commands, that is, by far, dependenc.do! Identically and independently distributed value is the predicted value this before, but you will use it a easier... ) values for avg_ed grad_sch and col_grad data that was in need a. The skewness greatly with the collin command displays several different measures of,. Plots just a random scatter of points are of great concern for us, you can how... Not, Stata will report where the command is located, and was cleaner! Votes can not reject that r is normally distributed inter-quartile range and assumes the of... Will consider the following is a problem of nonlinearity has not been completely solved yet influence! Simple linear regression in chapter 1 for these analyses are greater than 10 may merit further investigation increases academic. Economists. the distribution label each marker with the mlabel ( ) -returns for the potential! Estimator to compute thevariance-covariancematrix gen treated = ( country > 4 )!... Below we use the elemapi2 data file by typing use https: //stats.idre.ucla.edu/stat/stata/webbooks/reg/wage from within Stata if! Linear combinations of one another make individual graphs of crime with other building-block packages such as the product of and. On datasets with extreme combinations of one another observations of about firms and years... A histogram with narrow bins and moving average = result > that folder with the. An observation that is we wouldn ’ t look too bad and we shouldn t.

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