How do you do simple random sampling in Stata?
There are two commands in Stata that can be used to take a random sample of your data set. Use the sample command to draw a sample without replacement, meaning that once an observation (i.e., case, element) has been selected into the sample, it is not available to be selected into the sample again.
What is an observation in Stata?
To refer to a variable in Stata, you simply type its name. To refer to a particular observation in a variable, you type varname[n], where n is the observation number. For example, observation 7 in variable GDP could be called by typing GDP[7].
What is set OBS in Stata?
set obs changes the number of observations in the current dataset. # must be at least as large as the current number of observations. If there are variables in memory, the values of all new observations are set to missing.
What is Runiform in Stata?
runiform(r, c) returns an r × c real matrix containing uniformly distributed random variates over (0, 1). runiform() is the same function as Stata’s runiform() function. runiform(r, c, a, b) returns an ir×jc real matrix containing uniformly distributed random variates over (a, b).
Why is sampling with replacement a problem?
When we sample with replacement, the two sample values are independent. Practically, this means that what we get on the first one doesn’t affect what we get on the second. Mathematically, this means that the covariance between the two is zero. In sampling without replacement, the two sample values aren’t independent.
What is Strpos in Stata?
Description. strpos(haystack, needle) returns the location of the first occurrence of needle in haystack, 0 if needle does not occur, or 1 if needle is empty. strrpos(haystack, needle) returns the location of the last occurrence of needle in haystack, 0 if needle does not occur, or 1 if needle is empty.
What is N Stata?
_n is Stata notation for the current observation number. _n is 1 in the first observation, 2 in the second, 3 in the third, and so on. _N is Stata notation for the total number of observations.
What does Rnormal mean in Stata?
rnormal() standard normal (Gaussian) random variates, that is, variates from. a normal distribution with a mean of 0 and a standard deviation. of 1. rnormal(m)