Description Usage Arguments Details Value Author(s) See Also Examples
Produces table of relevant descriptive statistics and inference for either one- or two-sample t-test. In the two-sample case, the user can specify whether or not observations are matched, and whether or not equal variances should be presumed. Can also perform a test of equality of proportions (Wald based or exact binomial based).
1 2 3 4 |
var1 |
a (non-empty) numeric vector of data values. |
var2 |
an optional (non-empty) numeric vector of data. |
by |
a variable of equal length to that of |
strat |
a variable to use instead of |
geom |
a logical indicating whether the geometric mean should be calculated and displayed. |
prop |
if |
exact |
must be |
null.hypoth |
a number specifying the null hypothesis for the mean (or difference in means if performing a two-sample test). Defaults to zero. |
test.type |
a string: one of |
var.eq |
a logical value, either |
conf.level |
confidence level of the test. Defaults to 95/100. |
matched |
a logical value, either |
more.digits |
a numeric value specifying whether or not to display more or fewer digits in the output. Non-integers are automatically rounded down. Any call to |
... |
only used in the generic S3 class. |
Missing values must be given by "NA"
s to be recognized as missing values. Any call to ttest()
is run by ttest.default()
, with user specified values in place of defaults in the appropriate places.
Prints a summary of the data and the corresponding t-test.
Variable |
the variable name supplied to the t-test function |
Group |
the group name: either the variable names supplied to the function or the names of the strata if the variable |
Obs |
Number of observations of each variable: includes missing values. |
Missing |
number of missing values in each data vector. |
Mean |
the sample mean of each data vector; also, the estimated difference in means in a two-sample test. |
Std.Err. |
the estimated standard error of the mean and of the difference in the two-sample test. |
Std.Dev. |
standard deviation estimates from the data. |
CI |
a confidence interval for the means, and for the difference in the two-sample test. This is at the confidence level specified in the argument. If |
Null hypothesis |
a statement of the null hypothesis. |
Alternative hypothesis |
a statement of the alternative hypothesis. |
t |
value of the t-statistic. |
df |
the degrees of freedom for the test. |
Pr |
a p-value for inference on the corresponding hypothesis test. |
Scott S. Emerson, M.D., Ph.D., Andrew J. Spieker, Brian D. Williamson, Travis Y. Hee Wai, Solomon Lim
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | #- Read in data set -#
psa <- read.table("http://www.emersonstatistics.com/datasets/psa.txt", header=TRUE)
attach(psa)
#- Perform t-test -#
ttest(pretxpsa, null.hypoth = 100, test.type = "greater", more.digits = 1)
#- Define new binary variable as indicator -#
#- of whether or not bss was worst possible -#
bssworst <- bss
bssworst[bss == 1] <- 0
bssworst[bss == 2] <- 0
bssworst[bss == 3] <- 1
#- Perform t-test allowing for unequal -#
#- variances between strata -#
ttest(pretxpsa, by = bssworst)
#- Perform matched t-test -#
ttest(pretxpsa, nadirpsa, matched = TRUE, conf.level = 99/100, more.digits = 1)
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