The measures of position such as quartiles, deciles, and percentiles are available in quantile function. Create 10 groups of firms based on thier market value in this example, we shall use the grunfeld data set and download it within stata from the stata server. Typically, a continuous variable might be divided into categories or groups. It differs from xtile because the categories are defined by the ideal size of the quantile rather than by the cutpoints, therefore yielding less unequaly sized categories when the cutpoint value is frequent, when using weights or when the number of observations in the dataset is not a product of. Be sure to diagnose your design and assess the distributions of your variables. Can anyone help with a computation of a variable in stata of spss. It is used to create tables of summary statistipcs as. Categorise statsdirect statistal analysis software. Converting panel data into percentiles to observe trends in stata. This article is part of the stata for students series. Ive only coded for singlesorted quartile portfolios in stata but now i need to. For 100 million observations, this took 31 minutes. In this article youll learn how to create new variables and change existing variables.
Creating and recoding variables stata learning modules this module shows how to create and recode variables. Stata then runs the next loop to combine the nine new data sets into one file. A way to do something quite similar in r using cut is found at create categorical variable in r based on range. Carpenter california occidental consultants, anchorage, ak abstract the meanssummary procedure is a workhorse for most data analysts. Spss will not stop you from using a continuous variable as a splitting variable, but it is a bad idea to try to attempt this.
Create a variable by dividing a variable by iqr in stata. Figure 2 is the screenshot of a help file from stata for the regress command help. Descriptive statistics using the summarize command stata. Is there any command that can do something in stata that is like the r version. Dependent variable summary statistics based on quartile of. Now we have to tell stata which variable is the identifier and which variable is time. Creating variable based on matching question and answer suffix hi r stata, ive got an ugly but functional bit of code that im trying to make more efficient because ive got a lot of variables and a lot of values many more than presented here. Collapsing a continuous variable example from stata the codebook command. How to generate quantile categories by groupvarlist. Descriptive statistics mean, median, variability 30 may 2011 tags. I am looking to create a categorical variable that contains 0,1,2,3 as four categories that represent four quartiles on ftehsp variable. Spssx discussion computing new variable based on percentiles. For example, you might want to convert a continuous reading score that ranges from 0 to 100 into 3 groups say low, medium and high.
Tip how to create quartile groupings of a continuous variable creating quartiles. From percentiles to observe trends part 2 by jeff meyer. After saving the new data set, stata will revert back to the original data set. Converting data into and out of stata ucla statistics. If you are new to stata we strongly recommend reading all the articles in the stata basics section. Stata is a powerful statistical software package, used by students and researchers in many fields. To get the same result as centile specify type 6, which gives 6378. Imagine that one has 10,000 ranges that are needing to go into var2. I was told that there is a function in spss that will compute a new variable based on designated percentiles e. This post demonstrates how to create new variables, recode existing variables and label variables and values of variables. Dear statalisters, does anyone know what the command is to get the interquartile range using stata. While some variables can be given a fairly mnemonic name, for others it is useful to see a more in depth description.
Variables are always added horizontally in a data frame. Descriptive statistics and visualizing data in stata bios 514517 r. Xtine is similar to statas xtile command, but is able to make more evenly. Basics of stata this handout is intended as an introduction to stata. Stata faq there may be times that you would like to convert a continuous variable into groups. The point here is that you want to create groupings that allow for the maximum. Stata module to calculate percentile and quantile for a. Turns out r has 9 types of quantiles, the default is 7. Then use those above and below the quartile values as high and low groupings.
The common function to use is newvariable oldvariable. Converting panel data into percentiles to observe trends. Stata has builtin commands ptile and xtile for calculating the quantile ranks of a variable. Descriptive statistics give you a basic understanding one or more variables and how they relate to each other. When it opens you will see a blank worksheet, which consists of alphabetically titled columns and numbered rows. Spss will see each unique numeric value as a distinct category. In this paper we argue that this approach is highly problematic and present several potential alternatives.
Following are examples of how to create new variables in stata using the gen short for generate and egen commands to create a new variable for example, newvar and set its value to 0, use. These notes are meant to provide a general overview on how to input data in excel and stata and how to perform basic data analysis by looking at some descriptive statistics using both programs. In this example, it allows us to combine the wage data from the ten deciles that we will be generating. Hi nick, thanks for your help, i really appreciate it and would definitely give it a try. Statistics summaries, tables, and tests summary and descriptive statistics create variable of quantiles. Regression of y on different quantiles of x in stata. Observing the data collapsed into groups, such as quartiles or deciles, is one approach. The simplest way is just to use summarize results directly. Create portfolios in stata using astile stataprofessor. Most often, these new variables will be based on other variables in the dataset. Stata create a variable by dividing a variable by iqr in.
In stata, you can generate a new variable using the command generate. Stata also has help files accessible through the main menu. How to create dummy variables using quartile information posted 04192017 2282 views i have a continuous variable called serumlvl and would like to create dummy variables using quartile numbers for the serum level so that i can compare its crude relationship with another categorical variable. In stata you can create new variables with generate and you can modify the values of an existing variable with replace and with recode. I have data on a dependent variable y and an explanatory one, x, and want to find out if there is a nonlinear relationship between theses by running regressions where the data is divided in quartiles from the lowest to the highest value of x. In the following example, stata will generate a new variable named var3 that is exactly the same as var1. Percentiles are calculated by ordering the values of a variable from lowest to highest, and then finding the value that corresponds to whatever percent you are. The gen allows you to create new variables based on other variables. For example, if we want to make 10 portfolios, values of the newvar will range from 1 to 10. Generate a variable equal to another variable already in the dataset. Throughout, bold type will refer to stata commands, while le names, variables names, etc.
Descriptive statistics excelstata princeton university. Making foreach go through all values of a variable. How to create dummy variables using quartile infor. I have the cps data attached and i want to show the income threshold of the top percentiles 90,95,99,99. How to create, rename, recode and merge variables in r. Let us load the auto dataset and compute the 75th percentile of price using stata s centile. Descriptive statistics and visualizing data in stata.
We first create a sample data set containing 3 continuous variables, x1, x2, and x3, which we would like to group into quintiles. Its speed efficiency matters more in larger data sets or when the quantile categories are created multiple times, e. Teaching\ stata \ stata version 14\ stata for logistic regression. Stata will then run the loop for x20, then x30, etc. In order to split the file, spss requires that the data be sorted with respect to the splitting variable. For example, i have a variable called test score and i want to collapserecode it into a variable that reflects low, medium, and high based on percentiles. Take the igm variable in the parametric sheet of the test workbook for example. Create a new variable based on existing data in stata. I know there is a command that gives you the iqr, upper and lower limits, median, etc. To create a new variable or to transform an old variable into a new one, usually, is a simple task in r. Below is a listing of all the sample code and datasets used in the continuous nhanes tutorial. Stata is available on the pcs in the computer lab as well as on the unix system. Creating and recoding variables stata learning modules. Output of program to generate proportions using stata.
Sometimes people find it useful to collapse a continuous variable into quintiles or quartiles. Since i didnt generate any variables in the program define. We saw how to work with the data editor in gsw 6 using the data editorthis chapter shows how we would do this from the command window. Here we use the generate command to create a new variable representing population younger than 18 years old. This should be repeatedlooped through a number of years, where each year has its own sheet. Generating discrete random variables with fabricatr. The last two lines open up the new data set and places the variable ptl at the top of the variable. Dependent variable summary statistics based on quartile of explanatory variable i am looking to create a table of summary statisticsmeans of different agricultural practices such as fallowing land, using intercropping, and manure application.