Basic Concepts

1
Basic Concepts

• a brief review

2
Research Studies

• Non-Experimental
• (Descriptive)
• Behavior is observed as it naturally occurs
• Advantage natural
• Disadvantage lack of control

• Experimental
• (Laboratory)
• Manipulate one variable to see the effect on
  another variable (cause-and-effect relationship)
• Advantage control (representative sampling,
  random assignment, manipulation)
• Disadvantage artificial ethical limitations

3
Variables

• Independent
• The variable manipulated by the researcher and
  is the cause of the behavior

• Dependent
• The variable measured by the researcher and is
  the effect of the independent variable

4
Variables

• The independent variable must have at least two
  conditions or levels
• age, gender, intelligence, aggression, anxiety

variable gender levels ???
5
What do you think?

• Gender differences in voting preference (Bush or
  Kerry)
• Variable gt Levels gt
• Variable gt Levels gt

6
Experimental Studies

• Does driving a SUV cause people
• to drive more aggressively?
• Independent Variable Dependent Variable

aggression
type of car (sedan, SUV)
7
Experimental Studies

• Control group The baseline or standard condition
  ? sedan
• Experimental group Receives some level of the
  independent variable ? SUV
• If behavioral changes occur when the independent
  variable is manipulated then we can conclude the
  independent variable caused changes in the
  dependent variable

8
Between-Participants

• The participants in each group are different
• Different people serve in the control and
  experimental groups
• Random sample
• Random assignment

9
Within-Participants (Repeated-measures)

• The same participants are used in all conditions
• Repeatedly taking measures on the same
  individuals
• The same people serve in the control and
  experimental groups
• Random sample
• NOT random assignment

10
For example

• How would you conduct a study in this class on
  the effects of a mnemonic device on memory?
• Between-Participants
• Within-Participants

11
Within vs. Between

• Between-Participants
• Advantage Minimizes order, carryover effects,
  and demand characteristics
• Weakness Requires more participants and time,
  groups may not be equal, less powerful
  statistically

• Within-Participants
• Advantage Requires less participants and time,
  increased statistical power (less variability due
  to individual differences)
• Weakness Order effects (practice and fatigue?
  counterbalance), carryover effects, demand
  characteristics

12
Statistics

• a brief review

13
Statistics Whats the point?

• Observations researchers make are DATA
• STATISTICS are a set of mathematical procedures
  for summarizing and interpreting data

14
Statistics Whats the point?

• Two types of statistics
• Descriptive Statistics (the easy ones)
  Summarize the data into one or two representative
  numbers
• Inferential Statistics Make inferences about
  the meaning of the data (infer that the results
  from the sample apply to the population)

15
Descriptive Statistics

• Measures of Central Tendency
  (characterizes the typical response)
• Mean The average of a group of scores
• Median The middle score in a distribution
• Mode The most frequent score

16
Descriptive Statistics

• Group A Group B
• 8 27
• 6 6
• 5  5
• 5 5
• 4 4
• 3 3
• 3 3
• 3                              3
• 1 1
• Mean 4.2 Mean 6.3
• Median ??? Median ???
  Mode ??? Mode ???

17

Descriptive Statistics

• Variability
• (The amount by which subjects
• vary from one another)
• Standard Deviation
• (The standard or normal amount the scores
  deviate or move away from the mean)

18

Descriptive Statistics

• SD ? (x M)2
• x each score
• M mean
• N total number of scores

N
19
For Example

• Scores
• 2, 2, 4 , 4
• Mean ???
• 2 2 4 4 / N
• 12 / 4
• 3

20
For Example

• Scores
• 2, 2, 4 , 4
• SD ???
• SD ? (x M )2
• SD (2 - 3)2 (2 - 3)2 (4 - 3)2 (4 - 3)2 /
  N
• SD 1 1 1 1 / 4
• SD 1

N
21
For Example

• Group A 0, 5, 10, 15, 20, 25, 30
• Mean 15.00 SD 10.00
• Group B 14, 14, 14, 15, 16,16, 16
• Mean 15.00 SD .93
• Group C 15, 15, 15, 15, 15, 15, 15
• Mean 15.00 SD ???

22
Descriptive Statistics in a Nutshell

• Central tendency tells you about the average
  person
• Variability tells you how much people differ from
  the average person
• Great for organizing and summarizing data but
  they are only 1/2 the picture

23
(No Transcript)
24
How do you deicide if group differences are
reliable and not due to chance alone?
25
Inferential Statistics

• It is impossible to study the entire population
  therefore we must use a sample of the population
• Inferences are made about the likelihood that the
  differences in a sample reflect true differences
  in the population
• Inferential statistics tell us if differences in
  the sample are large enough to conclude that
  there are differences in the population
  (moving from the sample to the
  population)

26
Inferential Statistics

• Data always consist of 2 components
• The participants actual value on the dimension
  being measured
• Errors of measurement

27
Inferential Statistics

• Inferential statistics establish a probability
  that the results are real (not due to error)
• Data with a probability (alpha level) less than
  5 (p .05) are regarded as statistically
  significant
• This means ? 5 times out of 100 the results are
  going to be due to random error

28
Points to Ponder

• Statistical significance allows us to say that
  our results are probably not due to chance
•  
• Significance only refers to statistical
  probability, not to the theoretical or practical
  importance

29
Levels of Measurement
30
Choosing a Statistic
My research question is about
t test, ANOVA
Chi-Square
Correlation Coefficients
Ordinal Interval/Ratio
Interval / Ratio
Nominal