# Performing a t-test for a population mean using raw data

A t-test for a population mean helps a researcher answer the question: "Is the mean of the population of measurements a particular value?"

### Minitab 14 Procedure

1. Select Stat >> Basic Statistics >> 1 Sample t ...
2. If it is not already done so, click on the radio button labeled "Samples in columns."
3. Select the variable you want to analyze — by clicking or by highlighting and clicking once on "Select"— so its name appears in the box labeled "Samples in columns."
4. In the box labeled "Test mean," type the assumed value of the mean under the null hypothesis.
5. Select "Options"... Ignore the box labeled "Confidence level." For the box labeled "Alternative," select the direction of the alternative hypothesis (less than, not equal, greater than). Select OK.
6. Select OK. The output will appear in the session window.

### Minitab 13 Procedure

1. Select Stat >> Basic Statistics >> 1 Sample t ...
2. Select the variable you want to analyze — by clicking or by highlighting and clicking once on "Select"— so its name appears in the box labeled "Samples in columns."
3. In the box labeled "Test mean," type the assumed value of the mean under the null hypothesis.
4. Select "Options"... Ignore the box labeled "Confidence level." For the box labeled "Alternative," select the direction of the alternative hypothesis (less than, not equal, greater than). Select OK.
5. Select OK. The output will appear in the session window.

### Example

The US National Research Council currently recommends that females between the ages of 11 and 50 intake 15 milligrams of iron daily.

The iron intakes of a random sample of 25 such American females are found in the dataset irondef.txt.

Is there evidence that the population of American females is, on average, getting less than the recommended 15 mg of iron? That is, should we reject the null hypothesis H0: μ = 15 against the alternative HA: μ < 15?

#### Sample Minitab output

Close this window when finished.