Also create age2 to equal the square of age, and create lnwage to equal the natural log of annual earnings.
Create dummy variables for race (hispanic, black, and white) and sex (female and male). Separately tabulate race, school, and sex. Describe and summarize the data to better understand the data. And following that, a Stata program is included that would execute the commands for all 10 questions. If you get stuck, however, all 10 questions with Stata commands are repeated below. To best learn, try to work through all 10 questions by providing Stata commands and answers. The variables are race (1=hispanic, 2=black, 3=white), age, school (years of schooling), sex (F=female, M=male), and annual labor income. The data set contains five variables on 704 individuals. The data for this problem are in Stata format: wages.dta. © W.Stata Lab 5: Testing Coefficients Stata Lab 5: Testing Coefficients This information may be entered immediately with the ttesti command, with the appended "i" signalling the "immediate" variety of the t-test.įinally, Stata offers the possibility of running Hotelling's generalized t-test. Again, the level(.) option is available.Īnother interesting possibility is to do t-tests using information about group sizes, means, and standard deviations, instead of the raw data. Note that Stata will also accept a pair of equal signs. T-test to compare one mean with a hypothetical value (one sample t-test) The level(.) option described in the previous section is available as well. Note that Stata will also accept a single equal sign. Here, the appropriate version of the t-test is: Sometimes the two means to be compared come from the same group of observations, for instance, from measurements at points in time t1 and t2. These robust tests are more appropriate in the case of skewed variables. One of these alternatives uses the median instead of the mean in Levene's original formula and the other one the 10 per cent trimmed mean. Which delivers a robust test proposed by Levene in 1960 and two alternatives by Brown & Forsythe in 1974. 
To obtain the Bartlett test for equality of variances, or How do you know whether the two groups have the same variances? Use are different) and finally, with level(99) (abbreviated as l(99)) you can, in this case, request a confidence level of 99 per cent instead of the default level of 95, which is used in the calculation of confidence intervals. There are a few options that can be appended: unequal (or un) informs Stata that the variances of the two groups are to be considered as unequal welch (or w) requests Stata to use Welch's approximation to the t-test (which has the nearly the same effect as unequal only the d.f. The t-test is often used to compare the means of two groups. T-test for two independent samples (groups) The procedure commonly called t-test, however, refers to a test of the difference between two means (one of which might be a hypothetical value against which the mean of an observed variable is tested). Gosset) more than 100 years ago, is used for a number of testing purposes. The t distribution, developed by "Student" (a pseudonym of W. Multiple Imputation: Analysis and Pooling Steps.Confidence Intervals with ci and centile.Changing the Look of Lines, Symbols etc.
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