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# SpectrumHealthResearch / t-test Public

Calculate independent samples t test using summary statistics

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# Calculate two sample Student's t-test with summary statistics

These are simple scripts to facilitate the computation of the two independent samples Student's t test when only the summary statistics of the data are available, but not the raw data. To compute the t statistic, you will need the following:

• Group means
• Group standard deviations
• Group sizes

## Instructions

### R

#### Installation

The function is housed in an R package. To use the function, first you must install the package. To do so, execute the following in your R console:

```if (!require(devtools)) install.packages("devtools")
devtools::install_github("SpectrumHealthResearch/t-test/R")```

#### Example

```# Load the package into your session
library(stt)

# Using chickwts data from datasets
summary_chicks <- tapply(
chickwts\$weight,
chickwts\$feed,
function(x) c(mean = mean(x), sd = sd(x), n = length(x))
)

# We now have a named list of vectors containing summary stats
summary_chicks

# Execute the t test using summary stats
with(summary_chicks,
summary_t_test(
linseed["mean"],
soybean["mean"],
linseed["sd"],
soybean["sd"],
linseed["n"],
soybean["n"],
alternative = "less",
method = "sat"
)
)

## 	Two Sample t-test (satterthwaite)
##
## data:  summary statistics
## t = -1.3246, df = 23.63, p-value = 0.09899
## alternative hypothesis: true difference in means is less than 0
## 95 percent confidence interval:
##     -Inf 8.09536
## sample estimates:
## difference in means
##           -27.67857

# Compare with stats::t.test using raw data
t.test(
weight ~ feed,
chickwts,
feed %in% c("linseed", "soybean"),
alternative = "less"
)

## 	Welch Two Sample t-test
##
## data:  weight by feed
## t = -1.3246, df = 23.63, p-value = 0.09899
## alternative hypothesis: true difference in means is less than 0
## 95 percent confidence interval:
##     -Inf 8.09536
## sample estimates:
## mean in group linseed mean in group soybean
##              218.7500              246.4286```

### SAS

There are many ways to make use of this program. One suggested route:

1. Clone this repository or download the SAS code in the SAS folder.
2. Run the macro definition in the source editor or using `%include`.
3. Run the macro call.

Calculate independent samples t test using summary statistics

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