I need someone to complete my psychology statistic homework

Perillo Stats 1

Independent t-Test Example in SPSS

A group of middle schoolers (n = 20) and college students (n = 29) studied a list of 30 words, and later tried to recall as many words from the list as they could.

A researcher wants to test the hypothesis that college students, on average, would be able to remember more words from the list than middle schoolers would.

The datafile AgeWords.sav contains the data for all 49 participants.

Step 1: What test should we use to test this hypothesis?

Because we are comparing TWO groups of people, and our dependent variable is continuous (i.e., number of words remembered), we use an independent t-test.

Step 2: How do we run this test in SPSS?

 Go to “Analyze”  “Compare Means”  “Independent Samples t-Test”

 The “Test Variable” is our dependent variable (i.e., number of words recalled).

 The “Grouping Variable” is our independent variable (i.e., age – that is, whether each person is in middle school or college). But how do we get rid of those question marks?

Perillo Stats 2

Before we can run the test, we need to click “Define Groups” to tell SPSS which two groups to compare.

Under “Variable View,” we see that “Age” is coded as either 1 (Middle School) or 2 (College).

So, we enter these two numbers (1 and 2) under “Define Groups,” and when we click “Continue” we will see that these numbers have replaced the question marks that were there earlier.

Step 3: How do we read the output from SPSS?

1: Our sample consisted of n = 20 middle schoolers and n = 29 college students.

2: On average, our middle schoolers recalled 16.30 words (SD = 3.29), and our college students recalled 19.48 words (SD = 3.19).

3: These are the t (-3.39) and df (47) values for our t-test. We will need to include these in our write-up of the results, but they aren’t terribly interesting on their own.

4: This is our p-value (p = .001), which tells us if our hypothesis was supported (or not).

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Step  4:  How  do  we  calculate  the  effect  size?  

Navigate to the online effect size calculator: https://www.psychometrica.de/ effect_size.html#cohenb (link is in D2L). Choose calculator #2 - Comparisons of groups with different sample sizes.  

2. In  the  chart  above,  middle  school  students  are  listed  as  group  2.  To  make  sure  the  signs match,  enter  the  mean,  standard  deviation,  and  n  for  middle  school  students  in  Group  2  in the  effect  size  calculator.

3. This  is  our  Cohen’s  d  effect  size  (-0.98).  It  tells  us  the  strength  of  the  effect.

4. These  are  the  95%  confidence  intervals  for  the  effect  size  (-1.59, -0.38).  This  means we  have  a  95%  chance  of  the  true  value  of  our  effect  size  falling  between  these  numbers.

Because  our  Cohen’s  d  is  above  |.80|,  we  can  classify  it  as  a  large  effect  size.  The  amount   between  the  confidence  intervals  does  not  include  0,  which  means  the  effect  size  can  most   likely  be  trusted.  Given  the  size  of  the  confidence  intervals,  though,  it  means  our  true  effect   size  may  be  smaller  than  we  found.    

Perillo Stats 3

1. In  the  chart  above,  college students  are  listed  as  group  1.  To  make  sure  the  signs match,  enter  the  mean,  standard  deviation,  and  n  for  college  students  in  Group  1  in the   effect  size  calculator.

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1) We  always  begin  our  write-up  by  explicitly  stating  our  hypothesis.

2) Then,  we  name  which  test  we  did,  and  explain  what  the  test  showed.  Did  we,  or didn’t  we,  find  a  significant  difference/relationship?  This  is  where  we  will  provide our  test  statistic  (in  this  case,  our  t  value),  degrees  of  freedom,  our  p-value,  our effect  size,  and  the  confidence  intervals  for  the  effect  size.

3) Finally,  we  describe  each  of  the  groups  that  our  test  compared,  by  providing  the sample  size  (n),  mean  (M),  and  standard  deviation  (SD)  for  each  group.

4) Notice  that  all  non-Greek  letters  are  italicized,  every  equals  sign  has  a  space  both before  and  after  it,  and  every  number  is  rounded  to  two  decimal  places.

a. If  p  values  are  listed  on  SPSS  as  .000,  those  should  be  written  up  as  p  <  .001.

Perillo Stats 4

Step 5: How do we write up the results in APA format?

We hypothesized that college students would be able to recall significantly more words from a list than middle schoolers would. An independent samples t-test found a significant difference between these two groups, t(47) = -3.39, p = .001, d = -0.98, CI.95 = -1.59, -0.38. Supporting our hypothesis, college students (n = 29) recalled significantly more words (M = 19.48, SD = 3.19) than middle school students did (n = 20; M = 16.30, SD = 3.29).

A few notes about our write-up...