Transcript Slide 1

Chapter 7
Analyzing and Interpreting
Quantitative Data
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
By the end of this chapter,
you should be able to:
Describe the process of preparing and organizing your
data for analysis
Identify the procedures for analyzing your descriptive
research questions
Identify the procedures for analyzing your inferential
research questions or hypotheses
Recognize how to design and present results in tables,
figures, and a results section
Describe a discussion section of a research report that
interprets the results
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.2
Preparing the Data for Analysis:
Inputting Data
Score data by assigning numeric codes to
responses
Create a codebook
Use information from instruments when
possible as a part of coding scheme
Create a data file in data grid
Create variable, value labels
Clean database, missing values
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.3
Determine Types of Scores to Analyze
Single item
Summed scores
Difference scores
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.4
Selecting a Statistical Program
Statistical Package for Social Sciences (SPSS)
most popular
Other programs
–
–
–
–
Minitab
Statview
SAS (JMP/JMPIN)
StatPac
Use mainframe, PC, or Mac platforms
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.5
Conducting Descriptive Analysis
Measures of central tendency (value or score
that represents the entire distribution)
– Mean: Typically called the “average”
– Median: The value or score that divides the top half
of a distribution from the bottom half
– Mode: The value or score that occurs most often
Measures of variability (describes the “spread”
of the scores
– Range: The difference between the highest and
lowest scores
– Standard deviation: The standard distance the scores
are away from the mean
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.6
Conducting Descriptive Analysis
Measures of relative standing
– Percentile rank: The percentage of participants in
the distribution with scores at or below a
particular score
– Calculated score: Enables a researcher to
compare scores from different scales
– Z-Score: A popular form of the standard score,
has a mean of 0 and a standard deviation of 1
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.7
Running Descriptive Statistics
Descriptive Statistics
Central Tendency
Mean
Median
Mode
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Variability
Relative Standing
Variance
Z-Score
Standard Deviation Percentile Ranks
Range
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.8
Conducting Inferential Analysis
Hypothesis testing: A procedure for making
decisions about results by comparing an observed
value of a sample with a population value to
determine if no difference or relationship exists
between the values
Confidence interval: The range of upper and
lower statistical values that is consistent with
observed data and is likely to contain the actual
population mean
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.9
Conducting Inferential Analysis (cont’d)
Effect size: A means for identifying the practical
strength of the conclusions about group
differences or about the relationship among
variables
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.10
Conducting Hypothesis Tests
Identify a null and alternative hypothesis
Set the level of significance (alpha level) for
rejecting the null hypothesis
Collect the data
Compute the sample statistic
Make a decision about rejecting/failing to
reject
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.11
Computing the Samples Statistic
Inferential Statistics
Continuous (iv)
Continuous (dv)
Categorical (iv)Continuous (dv)
Continuous (iv)Categorical (dv)
Categorical (iv)Categorical (dv)
Parametric
Parametric
Parametric
Chi-Square
Nonparametric
Nonparametric
Nonparametric Analysis
Pearson
Correlation
Coefficient
Spearman T-Test
Rho
Mann- Discriminant Point
Witney Analysis
Biserian
U-Test
Correlation
Regression
Coefficient
Kendall’s Analysis of
Tau
Variance
Kruskall
Wallis
Test
Analysis of
Covariance
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Phi
Coefficient
Friedman
Two-Way
Anova
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.12
Selecting an Appropriate Statistic
Determine the type of quantitative research
question or hypothesis you want to analyze
Identify the number of independent variables
Identify the number of dependent variables
Identify whether covariates and the number of
covariates are used in the research question
or hypothesis
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.13
Selecting an Appropriate Statistic
Consider the scale of measurement for your
independent variable(s) in the research
question or hypothesis
Identify the scale of measurement for the
dependent variables (e.g., continuous or
categorical)
Determine if the distribution of the scores is
normal or skewed
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.14
Normal Curve
34%
34%
13.5%
13.5%
2.5%
-3
2.5%
-2
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Mean
+1
-1
Standard Deviations
+2
+3
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.15
The Normal Curve of Mean Differences
of All Possible Outcomes If the Null
Hypothesis Is True
Reject the
Null
Hypothesis
Extremely Low
Probability Values
If Null Hypothesis
Is True (Critical
Region)
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
High Probability
Values If the Null
Hypothesis Is True
Alpha=.025
Alpha=.025
Two-Tailed Test
Reject the
Null
Hypothesis
Extremely Low
Probability Values
If Null Hypothesis
Is True (Critical
Region)
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.16
Outcomes of Hypothesis Testing:
Type I and Type II Errors
Decision Made by
the Researcher
Based on the
Statistical Test
Value
Reject the
Null
Hypothesis
Fail to Reject the
Null Hypothesis
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
State of Affairs in the Population
No Effect:
Null True
Type I Error
(false positive)
(probability =
Alpha)
Correctly not
rejected:
no error
Effect Exists:
Null False
Correctly
rejected:
no error
(probability =
power)
Type II Error
(false negative)
(probability =
Beta)
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.17
Reporting the Results
Tables summarize statistical information
– Title each table
– Present one table for each statistical test
– Organize data into rows and columns with simple and
clear headings
– Report notes that qualify, explain, or provide
additional information in the tables, which can be
helpful to readers. Notes include information about
the size of the sample reported in the study, the
probability values used in hypothesis testing, and the
actual significance levels of the statistical test
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.18
Reporting the Results (cont’d)
Figures (charts, pictures, drawings) portray
variables and their relationships
– Labeled with a clear title that includes the number of
the figure
– Augment rather than duplicate the text
– Convey only essential facts
– Omit visually distracting detail
– Easy to read and understand
– Consistent with and are prepared in the same style as
similar figures in the same article
– Carefully planned and prepared
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.19
Reporting the Results (cont’d)
Detailed explanations about statistical results
– Report whether the hypothesis test was significant or
not
– Provide important information about the statistical
test, given the statistics
– Include language typically used in reporting statistical
results
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.20
Discussing the Results
Summarize major results
Explain why they occurred
Explain the implications of the results for the
audiences
Advance limitations
Suggest future research
John W. Creswell
Educational Research: Planning, Conducting, and Evaluating
Quantitative and Qualitative Research, third edition
Copyright © 2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
7.21