Subject: Experimental Study of the Effect of Interruption on Office Work
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Date: Tue, 13 Jan 2004 01:33:17 +0300

Experimental Study of the
Effect of Interruption on Office Work
Experiment 1: Types of
Interruptions

a study
made at UCSD for Electricité de France, in collaboration
with

Saadi
Lahlou, EDF, by

David
Kirsh, Thomas Rebotier, Clarissa Reeves and Mark Remy,
UCSD

Contents:

Methods

Results

Table 1:
Types of Interruptions

Figure 1: Sequence of
experimental events

Figure 2: Main
Effect

Figure 3: Long and
Short Interruptions

First Experiment

Before we can address the question
of a recovery device, we needed to measure the effect of various types of
interruptions in a controlled yet ecological setting.  This was the goal of the first
experiment, where interruptions of either a cognitive or a social kind were
hindering a realistic task.

Methods

Participants

Adult participants were 44
volunteers from Introductory Psychology classes at the University of California,
San Diego.  There were an equal
number of males and females, and 22 of the subjects participated in the
cognitive interruption task and 22 participated in the social/personal
interruption task.  No participants
were aware of the predictions or purpose of the experiment.

Stimulus
Materials:

The materials and stimuli were created by adding handwritten
changes to a five-page UCSD undergraduate anthropology essay, consisting of,
spelling, grammatical, and punctuation errors, inserting, deleting or
rearranging words/phrases and formatting modifications (see Appendix A).  An unedited version of the document was
created in Microsoft Word and was presented in black on a light gray background
via a Pentium computer on a 21 inch color monitor (800 x 600 lines of
resolution).

This study was run as a between-subjects design in which
participants were tested on either the cognitive or social/personal
interruptions.  Table 1 depicts the
four interruptions conditions which were created for each type of interruption,
two that were short (30 seconds) and two that were long (2 minutes) in
duration.

Design and Procedure

The cognitive and social interruptions were conducted under
identical conditions in a small, quiet room.  Participants were asked to add the
handwritten corrections noted on the hardcopy of the essay into the unedited
document on the computer.  Subjects
were instructed to organize the materials in any way that they preferred and to
proceed at their own pace.  The
testing session was recorded by video and the subjects’ corrections to the
document were recorded on the computer.

Figure 1 illustrates the testing session sequence.  There was an initial two-minute
introduction to the test, followed by the first long interruption.  After another two-minute on-task stage,
there was a 30 second short interruption with another two-minute on-task
stage.  This was followed by another
short interruption, with a two-minute on-task stage and finally a long
interruption with a final two-minute on-task stage for a total of 15 minutes of
testing.  A baseline measurement of
productivity, consisting of an eight-minute period of uninterrupted editing, was
also administered either before or after the testing session, with the order
counterbalanced across subjects.  To
ensure that the subjects fully comprehended the task and were familiar with the
computer equipment they were first provided with a practice paragraph to
correct.

Results

Our expectations were that interruptions would slow down
performance. We indeed found this effect on average: the baseline means were of
40.93 corrections for 306 words read, whereas the interruption means were 39.2
corrections for 292 words read; on the corrections alone this is significant
F(1,43)= 4.325, p=.044.

The effect was most manifest at the beginning of the
experiment.  This is illustrated in
Figure 2.  If we look at the first
half, for which the subjects contribute baseline data and half the subjects
interruption data, we see that the mean number of words read is 347 for the
baseline versus 308 for the interruptions; this difference is significant,
F(1,43)=5.458, p=.024.  The mean
number of corrections is also higher for the baseline: 41.2 versus 37.1,  not significant by itself (p=.13).  In the second half, there is on average
no effect:  275 words
(interruptions) versus 269 (baseline), and 41.1 corrections (interruptions)
versus 41.4 (baseline).  Thus, a
first conclusion that this study suggests is that interruptions affect people
more strongly when they are not yet trained.

We were also interested to find out whether there was a
difference between the two types of interruptions (cognitive vs. social).  The results did not support the idea
that the two different types of interruptions have different effects.

The real surprise was the breakup by interruption
duration.  Long interruptions are
much more disturbing than short interruptions.  In fact, for “trained” subjects (the
data from the second half of the experiment), short interruptions seem to
facilitate rather than slow down performance.  In the first half of the experiment, the
penalty for short interruptions is 15 words less than baseline (332 vs. 347) but
the penalty for long interruptions is 62 words (285 vs. 347), the difference
between the long and short interruption word counts is significant F(1,21)=15.8,
p=.001.  The difference is reversed
but less sensible (p=.26) on the correction count (41.2 for the baseline, 38.1
for long interruptions, 36.4 for short interruptions).  In the second half data, the difference
is much stronger: both types of interruptions facilitate slightly the word count
(baseline: 269, long interruptions: 272, short interruptions: 276, non
significant difference), but on the correction count, the long interruptions
penalize where the short interruptions facilitate (baseline: 41.6, long
interruptions 38.1, short interruptions 44.1), the difference between the long
and short interruptions is significant: F(1,21)=10.6 p=.004.  On the basis of only one experiment it
can be presumptuous to assert that interruptions sometimes facilitate
performance, but our data tend to suggest that it can occasionally be the
case.  Why? Possibly because
subjects loose interest with the task when it lasts too long.  A short interruption does not have the
more destructive effects of  long
interruptions, but allows the worker to refresh his attention.

Gender was not found to have any significant influence.

Interruption Length

Cognitive

Social/Personal

Short

(30
seconds)

Look
up a Phone Number

in the
UCSD Directory

Discuss
Favorite TV Program

Short

(30
seconds)

Sort a
Deck

Of
Cards by Suit

Phone
Call to check

the
Weather Conditions

Long

(2
minutes)

Logical
Reasoning

Question

Idle
Conversation

Long

(2
minutes)

Identify
Locations

on a
Subway Map

Journal
about

Fondest
Memory

Table 1:
Description of Cognitive and Social/Personal Interruptions

Figure 1: Sequence of
Experimental Task Administration

Figure 2: Interruptions degrade
performance but not so much in second half.

Figure 3: Apparently Short
Interruptions aren't nearly as disruptive as long interruptions.  For practiced subjects, they even look
like they make the subjects improve
.