Hi I need help fairly quick. Could someone please help with these 3 questions?

T-tests are used when you want to examine differences but you do not know everything about the population. There are three types of t-tests that you may choose to do: one-sample t-test, independent sample t-test, or dependent sample t-test. You can calculate these by hand, in SPSS, or in Excel. The instructions below can be used for SPSS and your textbook offers instructions for using Excel.

**Single-sample t-tests**

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**These tests are used when you want to determine the probability that a sample was drawn from a population with a known mean (μ) but with a standard deviation estimated from the sample.**

- Click on analyze, compare means, one-sample t-test
- Copy the variables you want to test into the Test Variables box
- Type the population mean into the Test Value box
- Click on options to get:
- Confidence intervals (95% is default)
- Exclude cases analysis by analysis
- If some data is missing, this will drop the data only in analyses where that data is missing.
- Exclude cases listwise
- If you are doing multiple t-tests and have missing data, this will drop participants who have missing data from all t tests
- Click on continue, ok
- The output will display the t-statistic, degrees of freedom (n-1), significance (two-tailed), and the confidence interval

**Independent sample t-test**

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**These tests are used when you want to determine the probability that two samples were drawn from the same population with unknown means and standard deviations; both of which are estimated from the sample. No population parameters are specified.**

- The data should be entered in one column and should be named as your dependent variable.
- You will need another column of data to identify each group according to number. So, it is a good idea to have two columns of data (one for the IV and one for the DV).
- For the IV column, you should use two consecutive numbers (I usually use 1 and 2)
- Also, be sure to use variable view to name your variables (otherwise this can become very confusing)

Ø First, we need to calculate means for the purpose of interpretation.

Ø Go to analyze, compare means, means

Ø Put your IV in the grouping variable box and your DV in the dependent variable box.

Ø Click OK to get the means and standard deviations

Ø Now, you need to calculate your t-test

Ø Go to analyze, compare means, independent samples t-test

Ø Your IV is the grouping variable

Ø Click on define range and enter 1-2

Ø Put the DV in the dependent variables box.

Ø You can click on options to change the confidence interval (default is 95%)

Ø Click on OK

Ø The output will show you the t-statistic, the significance level, the standard error of the mean, and the confidence interval.

**Dependent samples t-test**

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**We use this t-test when we have a repeated measures design such as the same sample completes a pre and post-test and we want to know if there is a difference from one test to the other.**

Ø Go to analyze, compare means, paired sample t-test

Ø Select two variables and move into box

Ø Click on OK

Ø The output will give you means for each trial (or pre-post test measure) as well as the t-statistic and significance level

Let's try a few using the data below. Be sure to attach your printouts and answer the questions below.

*First, perform an independent sample t-test for gender (IV) and pretest scores (DV)*

*Were there significant gender differences? How do you know? Interpret the results statistically and in words.*

*2.Then perform an independent sample t-test for gender (IV) and posttest scores (DV) Were there significant gender differences? How do you know? Interpret the results statistically and in words.*

*3.Now, perform a paired (dependent) sample t-test for pretest and posttest scores.*

*Were there two scores significantly different? How do you know? Interpret the results statistically and in words.*

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**Data Set Homework 2 (*note 1 = males, 2 = females)**

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**Gender Pretest Posttest**

**1.00 50.00 80.00**

**1.00 50.00 70.00**

**1.00 80.00 70.00**

**1.00 80.00 50.00**

**1.00 70.00 50.00**

**1.00 70.00 50.00**

**1.00 60.00 60.00**

**1.00 60.00 80.00**

**1.00 90.00 80.00**

**1.00 90.00 90.00**

**1.00 90.00 80.00**

**1.00 80.00 90.00**

**1.00 80.00 90.00**

**1.00 70.00 70.00**

**1.00 70.00 80.00**

**1.00 50.00 80.00**

**1.00 50.00 70.00**

**1.00 50.00 70.00**

**1.00 60.00 60.00**

**1.00 70.00 80.00**

**2.00 50.00 70.00**

**2.00 40.00 50.00**

**2.00 40.00 80.00**

**2.00 70.00 80.00**

**2.00 50.00 70.00**

**2.00 50.00 80.00**

**2.00 50.00 90.00**

**2.00 60.00 90.00**

**2.00 70.00 90.00**

**2.00 40.00 80.00**

**2.00 40.00 80.00**

**2.00 30.00 70.00**

**2.00 30.00 70.00**

**2.00 50.00 60.00**

**2.00 60.00 80.00**

**2.00 40.00 80.00**

**2.00 70.00 80.00**

**2.00 50.00 70.00**

**2.00 60.00 70.00**

**2.00 70.00 90.00**

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