Casimiro, Haizelyn N.

Endaya, Dominique Francesca E.

Grumo, Rona Rose A.

POINT BISERIAL COEFICIENT OF

CORRELATION (rpb)

The point biserial correlation is a measure of association between a continuous variable and a binary variable (Simon, 2005-2008).

The formula, according to Vizcarra, 2003:

1rpb 2121

nn

nn

s

xx

x

Where: = Point biserial coefficient

= Mean of the interval or ratio scale variable of one group (x)

= Mean of the other group (y)

= Number of population of one group

= Number of population in the other group

= Total number of population ()

= Standard Deviation of the two groups

rpb

1x

2x

1n

2n

n

SD

EXAMPLE:The researcher would like to determine if the

scores of 16 students of the same school on a 20-point math test is associated with their gender. Boys

(X1)Girls (X2)

14 15

12 10

19 9

11 7

9 8

7 19

6 16

18 11

Total = 95

Total = 96

STEPS:1. Compute the mean of X1 and X2.

= 11.87 = 122. Compute the standard deviation of X and Y

using the formula:

1X 2X

N

x

N

xrpb 22

16

191

16

2659 2

294.11160

44.17

18.4SD

3. Substitute in the formula of rpb:

11616

)8(8

18.4

87.1112rpb

240

64

18.4

13.0

27.0013.0

017.0 Negligible Correlation

Testing the significance of rpb:The point biserial coefficient of correlation is

a special case of Pearson r and its interpretation is similar to each other. The t-test for rpb is used to determine their significant relationship.

Computed t = 0.064Critical t at .05 with 14 df = 2.14Decision = Not Significant

21

2

rpb

Nrpbt

2017.01

216017.0

t

999.0

064.0t

064.0t

Thank you

End of Presentation

[Simon, 05-08]Simon, Steve (2005-2008). Retrieved August 31,2009. Stats: What is a point biserial coefficient correlation?. Website: http://www.cmh.edu/stats/definitions/biserial.htm

[Vizcarra, 03]Vizacrra, Florante O., Ed. D.(2003) . Introduction To Educational Research

References