95% CI and Width for Mean # of hrs watching TV for Three Different Sample Sizes Sample SizeConfidence Interval Interval WidthStand DevStand Error N=1952.65-3.270.622.260.16.

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Presentation transcript:

95% CI and Width for Mean # of hrs watching TV for Three Different Sample Sizes Sample SizeConfidence Interval Interval WidthStand DevStand Error N= N= N=1,

Part IV Significantly Different Using Inferential Statistics Chapter 11 t (ea) for Two (Again) Tests Between the Means of Related Groups

What you will learn in Chapter 11 When to use a t test for independent means How to compute the observed t value Interpreting the t value and what it means

t Tests for Dependent Samples Determining the correct statistic

Computing the Test Statistic Numerator reflects the sum of the differences between two groups

Degrees of Freedom Degrees of freedom approximate the sample size Degrees of freedom can vary based on the test statistic selected For this procedure…  n – 1 (where n is the number of observations)

Chapter 7 7 Doing the t test Prozac GroupPlacebo Group

Chapter 7 8 Doing the t test Steps in the process Step 1:  Calculate Step 2:  Calculate

Chapter 7 9 Doing the t test Steps in the process Step 3:  Count the number of scores in each group. N 1 = # scores in Group 1. N 2 = # scores in Group 2.

Chapter 7 10 Doing the t test Steps in the process Step 4:  Calculate sample variance for both groups Step 5 : Do the math!! Be sure to solve within brackets first!!

Chapter 7 11 Significance testing Steps in the process Step 1:  Calculate the degrees of freedom N 1 + N 2 – 2 Step 2:  One- or two-tailed test of significance? Did you have a directional hypothesis or not?

Chapter 7 12 Significance testing Steps in the process Step 3:  Using the table, find the critical values of t using N 1 + N 2 – 2 degrees of freedom.  Page , the t distribution. Step 4:  Compare the obtained t with the critical value of t.

Chapter 7 13 You Try!! Participant ID PlaceboParticipant ID Treatment

So How Do I Interpret… t (24) = 2.45, p >.05  t represents the test statistic used  24 is the number of degrees of freedom  2.45 is the obtained value (from the formula)  p >.05 indicates the probability

Using the Computer SPSS and Pared Samples t Test

SPSS Output What does it all mean?