Non-experimental Correlational research

1
Non-experimental Correlational research

• Determine whether 2 or more variables are
  associated,
• If so, to establish direction and strength of
  relationships
• Observe variables as they are,
• cant manipulate them

2

• Causal - (Experimental)
• one variable directly or indirectly influences
  another.
• Correlational - (Non-experimental)
• Changes in one variable accompany changes in
  another.
• A relationship exists. Dont know if either
  variable actually influences the other.

3
Correlational research

• If correlation -- relationship exists,
• Predict from value of one variable, the probable
  value of the other variable.
• Variable used to predict is predictor variable
• Variable being predicted is criterion variable

4
Example Test Score

• Ten students took a Chemistry class and a Biology
  class together
• Compared final exam scores in two classes

5

• Students who get higher score in the Chemistry
  class also get higher score in the Biology class

6
Positive Correlation

• When scores of two variables move in same
  direction, these variables are positively (or
  directly) correlated
• Positive correlation between between chemistry
  final score and biology score
• When two variables are positively correlated,
  scatter plot shows a trend line that runs from
  lower-left to upper-right

7
Example Test Score

• The same students also took an Art class
• Compared final exam scores in Chemistry and Art

8
Example Scatter Plot

• Students who got higher score in Chemistry class
  got lower score in Art Class

9
Negative Correlation

• When scores of two variables move together in the
  same direction, we say that these variables are
  negatively (or inversely) correlated
• There is a negative correlation between between
  the chemistry final score and the art final score
• When two variables are negatively correlated, the
  scatter plot shows a trend line that runs from
  upper-left to lower-right

10
Example Test Score

• The same ten students also took an English class
  together
• Compare the English final score with the
  Chemistry final score

11
Score in Chemistry and Score in English are not
related
Test score
12
No Correlation

• When the change in one variable does not affect
  the change in another variable,
• these variables have no correlation
• No correlation between chemistry final score and
  English score
• When two variables have no correlation, the
  scatter plot shows the dots scattered throughout
  the grids

13
Correlation(SSS)
Size
Sign
Significance
14
SIGN

• (0 No systematic relationship)

15
Correlation Co-efficient
Negative
Positive
1
-1
0
16
Correlation Co-efficient

• indicates how strongly and in which direction two
  variables are correlated with each other
• A correlation co-efficient varies 1 to 1
• Indicated as r
• r 1 Perfect positive correlation
• If one variable increases by x, other variable
  also increases by x
• r - 1 Perfect negative correlation
• r 0 No correlation

17
Cannot say one variable causes the other in
correlational research

• The relationship between variables might be
  caused by an unobserved third variable -- third
  variable problem
• Direction problem
• Which came first? Which influences the other?
  (It may not have any influence on the other)
• E.g., childs level of aggression or amount of
  time watching violent TV?

18
Correlational research
(Non-experimental)

• When changes in one variable accompany changes in
  another, they covary -- a relationship exists.
• Does not mean they influence the other.
• Correlation does NOT imply causation

19
Correlational research

• Mens drive for thinness scores were positively
  correlated with weight gain.
• / Greater concern about being thin was
  associated with more weight gain. (Heatherton et
  al, 1997)
• Cant say concern for thinness causes men to gain
  wt.
• POSSIBILITIES
• Concern about being thin causes weight gain
• Weight gain causes concern about being thin
• X (3rd variable) causes weight gain and concern
  about being thin.