Child Development 133 
Research Methods in Human Development

Sections 02 & 06
Hembree            Fall, 2009


  Analyzing data

 I. Introduction

A. Conceptual perspective

1.      Comparing the means of the different groups



2.      Mean differences can be due to IV, confound, or error



3.      Comparing the results (means) we obtain with what we might expect by chance


B. The role of probability

1.      Chance and error



2.      Could these results have occurred by chance?

e.g.,  consider two means 12.0 and 13.0




All things being equal, we are more convinced when we see larger differences between means.  Why?


II. Hypothesis testing

A. Null hypothesis/Experimental hypothesis




B.  Fail to reject vs. reject




  • statistical significance



C.     Making decisions and making mistakes

Possible outcomes:






Reject Null

Fail to reject Null




What is true in

the population?


Null is false






Type II error



Null is true


Type I error






1.      Type I error 



2.      Type II error




Which error is worse?




3.      Power




Power is increased by:

  •  Reducing error


  •  Increasing # of subjects


  •  Increasing the effect size





III. Inferential Statistics

A. What do we mean by inference?


B.  t-test

t = association/lack of association

1.      calculate means

2.      calculate variance

3.      compute t

4.      find critical t, given specified alpha

5.      compare obtained t with critical t; make decision




degrees of freedom



C. Chi-square (handout)

  •  Used to test the association between two nominal (categorical) variables







Send problems, comments or suggestions to:

California State University, Sacramento
College of Education
Department of Child Development

Updated: August, 2009