Statistical Methods for Psychology

456 Chapter 13 Factorial Analysis of Variance

not this was their first child (primiparous versus multiparous) and on the basis of whether

this was a low-birthweight (LBW) infant or normal-birthweight (NBW) infant. Mothers of

LBW infants were further classified on the basis of whether or not they were under 18 years

old. The data represent a score on a 12-point scale; a higher score represents better

mother–infant interaction. Run and interpret the appropriate analysis of variance.

Primiparous Multiparous Primiparous Multiparous

LBW LBW LBW LBW LBW LBW LBW LBW
, 18. 18 NBW , 18. 18 NBW , 18. 18 NBW , 18. 18 NBW

4683797627210

657488425119

557389568498

346399457497

3976834574810

13.2 In Exercise 13.1 the design may have a major weakness from a practical point of view. No-

tice the group of multiparous mothers under 18 years of age. Without regard to the data,

would you expect this group to lie on the same continuum as the others?

13.3 Refer to Exercise 13.1. It seems obvious that the sample sizes do not reflect the relative fre-

quency of age and parity characteristics in the population. Under what conditions would this

be a relevant consideration, and under what conditions would it not be?

13.4 Use simple effects to compare the three groups of multiparous mothers in Exercise 13.1.

13.5 In a study of memory processes, animals were tested in a one-trial avoidance-learning task.

The animals were presented with a fear-producing stimulus on the learning trial as soon as

they stepped across a line in the test chamber. The dependent variable was the time it took

them to step across the line on the test trial. Three groups of animals differed in terms of the

area in which they had electrodes implanted in their cortex (Neutral site, Area A, or Area B).

Each group was further divided and given electrical stimulation 50, 100, or 150 millisec-

onds after crossing the line and being presented with the fear-inducing stimulus. If the brain

area that was stimulated is involved in memory, stimulation would be expected to interfere

with memory consolidation and retard learning of the avoidance response, and the animal

should not show any hesitancy in recrossing the line. The data on latency to recross the line

are as follows:

Stimulation Area

Neutral Site Area A Area B

50 100 150 50 100 150 50 100 150

25 30 28 11 31 23 23 18 28

30 25 31 18 20 28 30 24 21

28 27 26 26 22 35 18 9 30

40 35 20 15 23 27 28 16 30

20 23 35 14 19 21 23 13 23

Run the analysis of variance.

Exercises

The following problems can all be solved by hand, but any of the standard computer software

packages will produce the same results.

13.1 In a study of mother–infant interaction, mothers are rated by trained observers on the qual-

ity of their interactions with their infants. Mothers are classified on the basis of whether or