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Generate data sets with continuous, categorical, grouped and correlated data. Great for creating data sets for examples and for quality assurance testing. Data sets are created in standard .CSV format so they can be opened in most statistical programs such as SAS, SPSS, WINKS and into spreadsheet programs such as Microsoft Excel. Order now.

 

WINKS Statistical Software Manual

These WINKS statistics tutorials explain the use and interpretation of standard statistical analysis techniques for Medical, Pharmaceutical, Clinical Trials, Marketing or Scientific Research. The examples include how-to instructions for WINKS SDA Version 6.0 Software. Download evaluation copy of WINKS.

 


Paired t-test

Definition: Used to compare means on the same or related subject over time or in differing circumstances.

Assumptions: The observed data are from the same subject or from a matched subject and are drawn from a population with a normal distribution.

Characteristics: Subjects are often tested in a before-after situation (across time, with some intervention occurring such as a diet), or subjects are paired such as with twins, or with subject as alike as possible. An extension of this test is the repeated measure ANOVA.

Test: The paired t-test is actually a test that the differences between the two observations is 0. So, if D represents the difference between observations, the hypotheses are:

Ho: D = 0 (the difference between the two observations is 0)

Ha: D 0 (the difference is not 0)

The test statistic is t with n-1 degrees of freedom. If the p-value associated with t is low (< 0.05), there is evidence to reject the null hypothesis. Thus, you would have evidence that there is a difference in means across the paired observations.

Location in WINKS: The paired t-test is located in the t-test and Analysis of Variance menu.

See also: Repeated Measures Analysis of Variance. Also, if the differences have already been calculated, a single sample test of u = 0 would be equivalent to the paired t-test. The non-parametric counterpart to the paired t-test is Friedman's test.


Example: Paired t-test

The DIET.DBF database contains information on 8 subjects who were placed on a diet, and observed for several weeks. Before and after weights were taken. The results of a paired t-test analysis are:

-----------------------------------------------------------------
Repeated Measures Analysis Summary              C:\WINKS\DIET.DBF
-----------------------------------------------------------------

Number of repeated measures is 2
Number of subjects read in 8
-----------------------------------------------------------------
 Means and standard deviations for 2 repeated measures:
-----------------------------------------------------------------
1)REP1: mean = 169.625 s.d. = 8.07001
2)REP2: mean = 150.25 s.d. = 11.04213
Mean Difference = 19.375 s.d.(difference) = 14.78356
95% C.I. about Mean Difference is (7.01367, 31.73633)
Paired t- test
Calculated t = 3.70687 with 7 D.F. p = 0.0076 (two- sided)

 The t-test reports t = 3.71 and p = .008. For this evidence, you can conclude that the diet produced a significant amount of weight loss (look at the before and after means.)


Exercise - Paired t-test

A company was wondering which style of pepperoni pizza was most popular. It set up an experiment where ten people were each given two types of pizza to eat, Type A and Type B. Each pizza was carefully weighed at exactly 16 oz. After fifteen minutes, the remainders of the pizza were weighed, and the amount of each type pizza remaining per person was calculated. It is assumed that the subject would eat more of the type of pizza he or she preferred. Here are the data:

Subject

Pizza A

Pizza B

1

12.9oz

16oz

2

5.7

7.5

3

16

16

4

14.3

15.7

5

2.4

13.2

6

1.6

5.4

7

14.6

15.5

8

10.2

11.3

9

4.3

15.4

10

6.6

10.6

1. Perform a paired t-test.

2. What value of the t-statistic is calculated, what are the degrees of freedom for the test, what p-value is reported for this data?

3. Do people seem to prefer one type of pepperoni pizza over another? If so, which seems to be most liked?


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Analyze Data With WINKS

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Best value for an easy to use and extensive statistical program."
Basic edition starts at $99.
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"Winks is an excellent basic program that runs well on my laptop.  I find that I use it more than SAS"  - Dr. Jim Dickson, Iowa State University

  • Statistical Software designed for your needs -- Medical, Clinical Trials, Dissertation, Thesis, Business, Marketing, Agriculture, Forestry, Science and Research.

  • WINKS is an economical, reliable and simple to use statistical analysis tool designed to help students and researchers get the statistical answers they need quickly and without hassle.

  • It contains a wide range of statistical tests including many handy features not found in programs such as SPSS or SAS -- for example, easy analysis from summary data (as well as from raw data), nonparametric multiple comparisons, APA standard analysis write-up suggestions and more.

  • Newest additions to WINKS (ver 6.05) includes Grubbs Test for outliers  and Tukey Test for outliers, Kwikstat Data Generator evaluation edition, multiple comparisons in 2xc and rx2 crosstabulation (Chi-Square) analysis)  & Permutations and combinations calculator

  • Statistical test such as t-tests (paired t test, independent group t test/unpaired t test), ANOVA, regression, correlation, repeated measures, logistic regression, times series analysis, chi-square, Bland-Altman, Kruskal-Wallis, Mann-Whitney and much more.

  • Friendly interface with easy Excel-like data handling & graphs (reads and writes Excel files.)

  • FAST delivery to you when you order now

  • Print a brochure (pdf format)

  • Recent updates include

    • Added ability to calculate new column of z-scores for numeric variables.
    • Increased maximum groups to 40 for one-way ANOVA and one-way repeated measures (40 repeats).
    • Added editor option to create indicator variables from categorical variables.
    • Added Outcomes and Probabilities module that calculates combinations and permutations.
    • Added Grubbs & Tukey tests for outliers.
    • Added Multiple Comparisons of Proportions to Crosstabulations procedures for 2xc or rx2 tables
    • Updates are free to current users.

Read more about WINKS features.


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This page was last edited: 11/04/2008