Memory Decay and the Agenda-Setting Effect:
An Examination of Three News Media
The mental processing of information obtained through the mass media is
complex and elaborate. Individuals attend to, process and retain a
variety of information in many different ways. At the same time, the
media provide individuals with an endless stream of issue coverage.
covered today replace issues covered yesterday, and individuals somehow
must make sense of this coverage.
The end result of this mental processing of issue information is the mass
media's agenda-setting effect. Coverage of issues in the mass media
individuals salience cues by which they judge the perceived importance
Of concern here is how the rise and fall of coverage of issues on the mass
media agenda is related to the public agenda, given the fact that
individuals have a limited ability to retain information. Obviously,
individuals do not remember everything they read in the newspaper or
everything they view on television, especially as new information becomes
available to replace old information. In other words, an individual's
memory of information gained from the news media decays over time.
Watt, Mazza and Snyder (1993) took memory decay into consideration in
their investigation of the optimal agenda-setting time-lag. Basing
study on the memory decay curve first investigated by Ebbinghaus
Watt et al. reasoned that the effects of exposure to media messages
decay exponentially over time. Today's news will have a stronger
individuals than yesterday's news, and much more influence than news
covered days earlier. They found that the memory decay time-lags
for different issues: from 30 days for Iran to 600 days for inflation.
While the agenda-setting effect of various types of issues may decay
differently over time, the influence of different media also may differ.
For example, the influence of a visual medium, such as television, may
decay more rapidly than a verbal medium, such as newspapers. In
a national medium, such as a national television newscast, may have a
different decay time period than a local medium, such as a local
Thus, the present study will attempt to answer the following question:
Given the fact that an individual's memory of information gained from
mass media decays over time, what is the time period in which
agenda-setting effects disappear for three different news media? The
media examined are local newscasts, national network newscasts and a local
newspaper. The answer to this question has several important
First, this study addresses an important topic for research in the general
area of media effects. Since agenda-setting is "social learning," how
individuals learn about society is an important area of research.
Second, this study has important ramifications for agenda-setting
research. The results may offer insights into how individuals process and
retain information from different media.
Third, finding the memory decay time-lag in agenda-setting is imperative
for future researchers. It would give researchers guidelines for
future studies, especially for studies in which a specific type of
medium is included. In addition, the time-lag for agenda-setting
investigations is taking on greater significance in light of recent
attempts to employ complex statistical analyses, such as time-series
analyses (Zhu, Watt, Snyder, Yan and Jiang 1993) and path analyses (Wanta
and Hu, 1994). As statistical analyses increase in complexity, the
precision needed for measurements of media content is amplified.
One of the most important considerations that agenda-setting researchers
must address is what time frame they will employ in their analyses.
other words, researchers must decide how far back in time they will go
analyze media content prior to their field work. As Winter and Eyal
note, "Since most of these studies measure and compare the media and
public agendas over time, the temporal variable would appear to be
Time-lag selection is especially important in agenda-setting research,
since studies in this area investigate a causal hypothesis. Chaffee
argues that a time-lag that is too short will not capture the causal
relationship, but a time-lag that is too long is also a serious problem
because "there is always the danger that a causal effect will
over time if the researcher waits too long to measure it."
Salwen (1988) believes the time-lag question is important because
researchers need to confine their measures of media coverage to as short a
time period as possible because "any time discrepancies in the
of the public agenda may affect the public's evaluations of issue
Despite the importance of a precise time frame, many discrepancies remain
regarding the optimal time period to include in agenda-setting
Studies have examined issues in time frames as short as one week
1977; Becker and McCombs, 1977), and as long as nine months (Sohn,
Funkhouser (1973) compared media coverage across a decade with public
concern in the same time period.
Furthermore, even the few studies that have dealt specifically with the
time-lag question have produced inconsistent results. Table 1 lists
results of five studies that specifically examined the optimal
agenda-setting. The optimal time-lags varied from a four-month period
stretching from two to six months before the survey period (Stone and
McCombs, 1981) to zero to two weeks before the survey period (Eaton,
The varied results on the optimal agenda-setting time-lag, however, could
be due to methodologies employed. Stone and McCombs (1981) examined
news magazines: Time and Newsweek. Winter and Eyal (1981) studied one
issue (civil rights) from 1954-1976 and front-page coverage in the New
Times. Salwen (1988) also looked at one issue (the environment) and
coverage in the three largest daily newspapers serving Lansing, Michigan.
Zucker (1978) investigated four issues across time and coverage on the
three national networks. Eaton (1989) examined complete agendas based
bi-weekly data collected from three network broadcasts, four
three newsmagazines combined.
In addition, most of the research dealing with the time-lag question
examined one issue, or a series of single issues, across time. But given
the large number of "Type I" studies (McCombs, 1981) -- which examine
entire agenda of issues covered by the news media and an entire agenda
issues perceived as important by members of the public -- an
comparing complete media and public agendas is sorely needed. This
of examination allows for an investigation of the inter-relatedness of
ssues, an important consideration given the recent research that
that issues compete with each other in a "zero-sum" game (Zhu, 1992).
Previous research also has noted the possibility of differences between
the news media. Several researchers (Tipton, Haney and Basehart,
McClure and Patterson, 1976) have found that newspapers correlate
than television with voter agendas. Shaw and McCombs (1977) argue
television news might have a stronger short-term impact, but newspaper
content may have a more consistent effect across longer periods of time.
Zucker (1978), on the other hand, argues that at the national level,
public may be more influenced by the three networks' newscasts than by
newspapers because of television's accessibility.
A number of researchers also have suggested that national news media, to a
large degree, set the agenda of issues covered by local media. Breed
(1955), for example, suggests that news flows downward from the elite
dailies. In other words, small dailies learn coverage patterns from
Crouse (1972) similarly argues that the elite media, such as the New York
Times, influence the national agenda. Front-page coverage in the New
Times, he concludes, means prominent coverage in every other paper in
Thus, if smaller, more localized media react to the national media, the
national media may have a more immediate effect on the public. In
words, if local media follow national media coverage, issues in the
press will take longer to reach the general public than ones in the
national or regional media -- and consequently, will take longer to
influence the public agenda. However, since the national media may first
influence local media and then the public, the national media may show
slower decay in effect over time.
In addition, national media also devote more coverage to international and
national issues than do local media. Indeed, the traditional
agenda-setting question, which was employed here, asks respondents
the number one problem facing our country today?" Given that this
question addresses a national agenda, national media should have a stronger
agenda-setting effect than local media, which must devote significant
coverage to issues of only local concern. As a result, individuals may
demonstrate a slower memory decay for national issues covered by the
Added to the mix of factors surrounding the time-lag question is the role
of memory decay. Individuals do not remember equally as well media
across several days. Thus, the time period when agenda-setting effects
disappear is as important to researchers as a precise optimal
other words, at what point do individuals fail to recall the issue
information transmitted by the news media and accumulated in media
The study of memory and its decay dates back to before the turn of the
century. In a series of experiments conducted by Ebbinghaus (1885),
of words were learned and relearned on successive days. The amounts
time necessary for successful learning each day were noted and later
compared to each other in order to discuss the relationship between
information retention and time. From the resulting graph, Ebbinghaus --
and subsequent researchers who further upheld his findings --
that the "main characteristic (of human memory decay) is a rapid fall
immediately after learning and a gradual flattening out as the interval
prolonged. Forgetting becomes more and more gradual as time advances
(Woodworth and Schlosberg, 1954, p. 726)." Further, when Ebbinghaus
plotted his data against the logarithm of time, he observed that
declines approximately in proportion to the log of time (Woodworth and
Schlosberg, 1954, p. 726)."
Watt, Mazza and Snyder (1993) use this exponential expression of memory
decay over time when analyzing three issues presented in television
newscasts and their agenda-setting effects. In order to account for past
coverage of an issue in addition to current stories, Watt et al.
the Ebbinghaus curve. The resulting formula analyzes memory decay of
issue coverage and its effect on audience issue salience, while also
accounting for issue prominence (i.e., where it was placed within the
newscasts) and issue obtrusiveness (i.e., personal experience with an
by audience members).
In addition to altering the Ebbinghaus curve, Watt et al. use the concept
of a "time window" to account for past, accumulated coverage and
news stories about an issue. These time windows, or data sampling
of variable length, are used to determine "how long ... people
be affected by past stories in the media (Watt et al., 1993, p. 409)."
with Ebbinghaus' memory loss hypothesis, all issue coverage and
within the time window should proportionately decay. Given the ma
thematical fact that an exponential decay never reaches zero, Watt et al.
assume an eventual memory loss of 95 percent as the maximum loss of
impact in each time window. Their results show that different issues
their strongest agenda-setting correlations when analyzed within
time windows. Their memory decay time windows ranged from 12-60 days
Iran to 600 days for inflation.
Our study builds upon the groundwork laid by Watt et al. (1993). Instead
of examining individual issues in time windows of up to two years,
the present study investigates three different news media for shorter time
frames. Logically, a news report should not have an influence on
individuals 600 days later -- as found by Watt et al. Our study examines
daily coverage for six months for two news media and for 50 days for a
A telephone survey was conducted in a U.S. city in February 1994. The
area surveyed has a population of approximately 200,000 and is home to
large state university. Interviewers were students at this
The response rate was 60 percent.
The public agenda was determined by responses to the traditional
agenda-setting question: "What is the number one problem facing our country
today?" The 12 issues that were mentioned most often by respondents were
included in the study. The percentage of respondents who mentioned
issue as being the most important problem determined where the issues
ranked on the public agenda. The issues and the percentage of
naming them as the number one problem facing our country are listed in
Coverage of the 12 issues were then examined in three news media: the
national broadcasts of ABC World News Tonight, the local broadcasts of
evening news for the station with the highest ratings in the area
and a local morning daily newspaper serving the area. The ABC broadcasts
were coded through the Vanderbilt Television News Abstracts for the
months preceding the first day of our survey. In a few cases, always
either a Saturday or Sunday, ABC did not have a national broadcast.
maintain consistent time intervals, a broadcast of either CBS or NBC
coded on these days. The local television broadcasts were coded
station logs for the 50 days preceding the first day of the survey.
50 days of logs were available for this study. Finally, the front
the main news section were coded for the local daily newspaper for the six
months preceding the first day of our survey. Intercoder reliability
using Scott's pi averaged .89.
Each news story was weighted according to the distance in time from the
date of broadcast to the start of the survey period. The weights were
determined by the memory decay curve proposed by Ebbinghaus (1885).
more detailed description of the memory curve developed by Ebbinghaus, see
Woodworth and Schlosberg, 1954).
The weights are based on two main assumptions:
1. Individuals eventually retain only about five percent of all knowledge
that they learn. In other words, 95 percent of an individual's memory
2. Memory decay is not linear. That is, memory decays rapidly at first,
The effects of the accumulated weighted coverage were then examined for
each day of the study. For example, for Day 1, the day before the
beginning of the survey period, the coverage of issues televised on that
day was weighted by .05, again, under the assumption that memory
percent. For Day 2, the coverage of the day before the survey was
by .10 and coverage of two days before the survey was weighted by .05.
These weighted scores were then summed. For Day 3, weights ranged
to .08 to .05. Each subsequent day was weighted similarly, so that
coverage the farthest from the survey period was weighted by .05 and the
other dates were weighted based on the Ebbinghaus curve. Thus, the
coverage closest to our survey period received a heavier weight than
coverage farther back in time. Indeed, if Ebbinghaus' memory decay curve
is correct, information gained recently should be recalled more
than older information and thus should have a stronger agenda-setting
effect on individuals.
Spearman rank-order correlations were then computed examining the
relationships between the accumulated weighted coverage of the 12 issues
for each day in our analysis and the public agenda. In other words,
case of ABC newscasts, Spearman rhos examined the agenda-setting effect on
the public for time-lags ranging from one day before our survey period to
180 days before our survey period. If agenda-setting effects are most
pronounced after one day of coverage, for example, the Spearman rho for
day of coverage and the public agenda will be the largest in the study.
The Spearman rhos also will suggest where the public's memory decay
occurs. If the Spearman rhos are no longer statistically significant
30 days, for example, the results will suggest that the public's memory of
issue information decays after 30 days.
Methodological strengths and weaknesses
Several methodological aspects are important here.
First, the methodology here employs an entire agenda of issues. This was
the presupposition underscoring the original agenda-setting hypothesis
that an "agenda" of issues in the news media would influence an
issues that the public perceives as important. Thus, this analysis
returns to the area proposed in the original agenda-setting hypothesis.
Second, the analysis allows for the examination of several news media.
Logically, information from different media will be processed
among individuals. The passive processing of visual information from
television should produce results that are different from the active
processing of verbal information from newspapers. Local information also
should be processed differently than national information.
Third, the analysis allows for the examination of several memory decay
time lags. In other words, our analysis allows us to pinpoint to the
when the agenda-setting effect eventually decays in our study -- from
day to 180 days.
The major shortcoming of this study is that the analysis, by design, uses
aggregate data -- that is, data from an entire "public" rather than
individuals. Thus, the memory decay examined here is not an
decay, but rather a decay from an entire population of individuals.
Indeed, mental processes take place within individuals, not within a mass
of individuals. However, agenda-setting is a societal effect (see
and DeFleur, 1988). Thus, memory decay, while taking place within
duals, should be apparent in an analysis of a population of
which this process is occurring.
Spearman rank-order correlation coefficients for the three news media in
our study are listed in Tables 3 to 6 and are plotted in Figures 1 to
As Figure 1 and Table 3 detail, the ABC news broadcasts did not produce
any statistically significant Spearman rhos for the 12 issues in our
In other words, ABC news apparently did not have an agenda-setting effect
on the respondents in our study. This was contrary to what we initially
believed. We originally thought that national media would best match
public agenda because the agenda-setting question asks what the
believes is the most important problem facing "our country" today.
local media's concentration on local issues, we thought, would lessen
A secondary analysis of our data revealed that one issue -- international
problems -- received an extensive amount of coverage, but ranked low
public agenda (a tie for tenth). Indeed, the nature of national network
news implies that the networks provide extensive coverage of news
the world, which apparently did not catch the attention of respondents
Despite the quandary caused by the issue of international problems,
several trends are apparent. As Figure 1 and Table 3 show, the Spearman
rank-order correlations for the national news broadcasts of ABC
of their highest levels at Day 4 and Day 5 (r = .32), before decreasing.
Besides the first few days of the study, the lowest rho occurred after
days. The rhos showed a large increase again at Day 38 ( r = .36) and
reached their peak at Day 62 (r = .39). They remained at the r = .39
until Day 92, when they dropped to r = .36 and remained at this point
until the end of the study (Day 180).
To further examine the network television news-public relationship and to
guard against the results of our study being suppressed because of
patterns for this one issue, we re-analyzed the data after dropping
international problems from the analysis. The results of the 11 remaining
issues mirrored the results of the original 12, except for the fact
statistically significant findings resulted at several points.
As Figure 2 and Table 4 show, the Spearman rhos reached statistical
significance after only four days (r = .63), and dropped below the p < .05
level of statistical significance after Day 6. The lowest rho was
Day 14 (r = .41). The rhos reached statistical significance again at Day
38 (r = .65) and reached their peak at Day 62 (r = .68), before
slightly at Day 92.
Figure 3 and Table 5 detail the results of the Spearman rhos for local
television broadcasts. The rhos show several differences from the rhos
national news. Here, the Spearman rhos reached statistical significance
at Day 3 (r = .63) and peaked at Day 6 and Day 7 (r = .67). The rhos
decreased slightly, dropping below the level of statistical
Day 11. The rhos again reached statistical significance from Day 15 to
Day 17 and again at Day 20. All of the other rhos were not
significant at the p < .05 level. In addition, the rhos were
from Day 42 through the end of our study period at Day 50 (r = .51).
The Spearman rhos again were different for the local newspaper. As Figure
4 and Table 6 show, the rhos reached statistical significance at Day 8 (r
= .62). The rhos reached significance at the p < .01 level at Day 10
.71), and peaked at both Day 15 and Day 18 (r = .81). The rhos
back to the p < .05 level at Day 28 (r = .67), before leveling off at
34 through Day 59 (.61). The rhos were no longer statistically
at Day 84 (r = .54). The rhos were unchanged from Day 88 through the end
of our study (r = .51).
The purpose of this study was to examine how the agenda-setting effect
dissipates over time as individuals' memory of issue information
The findings are summarized in Table 7. The results show how
memory decay affects the agenda-setting process for the three news
A few similarities between the three media did emerge. First,
agenda-setting effects were evident early for all three media. Effects
appeared after four days for national network news (though only after
issue of international problems was dropped from the analysis), after
days for local news and after eight days for the local newspaper.
Second, the Spearman rank-order correlations showing agenda-setting
effects dropped below statistically significant levels relatively quickly
for all three news media. The rhos were no longer statistically
significant after six days for ABC news and after 11 days for local
newscasts. While the rhos for the local newspaper were statistically
significant for a much longer time -- until Day 85 -- the rhos did drop
below the p < .01 level at Day 28. Thus, memory of issue information
local newspapers did decay slightly after four weeks.
All of these results seem logical on the surface. Since individuals'
long-term memory is limited, a memory decay of a few weeks after an
agenda-setting effect of four to eight days appears plausible.
However, the agenda-setting effects, as demonstrated by the Spearman
rank-order correlations, showed several differences for the three news
media. Especially evident were differences in long-term memory decay
between the three news media examined here.
The agenda-setting effect for the local newspaper, for example, first
appeared on Day 8 and peaked at Day 15 and Day 18. The agenda-setting
effect decayed slightly at Day 28, and did not completely disappear
Day 85. Thus, the optimal time-lag for agenda-setting effects to
longer for the local newspaper than for either local or national
newscasts. Moreover, the local newspaper produced the strongest Spearman
rank-order correlation in the study (r = .81), indicating that in our
study, newspapers had a more powerful agenda-setting effect than
television, as both Tipton, Haney and Basehart (1975) and McClure and
Patterson (1976) found.
The agenda-setting effect also decayed much more gradually for the local
newspaper, since the agenda-setting effect for both local and national
broadcasts decayed only a short time after an early initial effect.
finding supports the argument of Shaw and McCombs (1977) that
news has a stronger short-term impact, but that newspapers have an
across longer periods of time.
The agenda-setting effect decayed at much different rates for both local
and national newscasts. The agenda-setting effect for local news
broadcasts disappeared in Day 11, though there was a minor effect for Days
15-17 and 20. The agenda-setting effect disappeared completely by Day
For national news, the agenda-setting effect was not evident at all, until
the issue of international problems was removed from the study. Then, the
agenda-setting effect was evident for Days 4 and 5, but decayed by Day 6.
However, the agenda-setting effect re-emerged at Day 38, then remained
through the end of our study period, 180 days in all.
Two important points should be made about the results for the national
newscasts. First, while an agenda-setting effect occurred early (Day 4
5), a consistent agenda-setting effect didn't appear until Day 38, or more
than five weeks before the survey period. Thus, the accumulated coverage
of five weeks led to the most consistent agenda-setting effect for the
newscast. In addition, the optimal time-lag for the strongest
agenda-setting effects -- when memory decay was accounted for -- was
between 62 and 92 days, or about two to three months before the survey
Second, individuals' memory decay for national news broadcasts was very
gradual. In fact, our findings suggest that the public's long-term
decay of issue information went beyond the six months of news coverage
examined in the present study.
One other possible explanation about the memory decay time period for the
national network news should be noted: Perhaps agenda-setting effects
really peaked at between four and five days, and memory of the issues
decayed at Day 6. The consistent agenda-setting effect found after Day
then, may be due to the fact that coverage patterns finally stabilized
here. Indeed, the media agenda changed little from Day 38 to Day 62
did not change at all from Day 62 through Day 92 and from Day 92
y 180. It seems eminently logical that individuals' abilities to
news coverage of issues should not last for two to three months. One
seems like a more logical time period for agenda-setting effects to
and two weeks seems like a logical time period for the memory of issue
information to decay.
The results of local television news coverage, meanwhile, appear more
easily decipherable. Here, the optimal time-lag for the strongest
agenda-setting effects to occur was six to seven days -- or about one week.
The memory decay of issue information followed one week later -- with the
Spearman rank-order correlations reaching one of their lowest points on
Day 14. (when r = .46). While agenda-setting effects again reached
statistical significance on Day 15, none of the Spearman rhos after Day 21
were statistically significant.
Thus, taken as a whole, both local and national television news media and
the local newspaper produced agenda-setting effects in a relatively
time before our survey period. The memory of the issue information
by respondents in our study also decayed in a relatively short time --
shorter than the Watt et al. (1993) study found.
The long-term memory decay of agenda-setting effects, however, showed a
wide discrepancy between the results of the local and national
This discrepancy, as with the lack of agenda-setting effects found for
news, again could be due to the types of coverage patterns of national
news. Besides the extensive coverage of international news, national
network news also may be more consistent in its coverage of all national
issues, while local news covers a wider range of issues. Since
s covers a more consistent agenda of issues, this agenda eventually
a point where it stagnates -- where issues no longer go up or down on the
agenda. In other words, the differences between issue ranks reaches a
stage where only a major event that receives a staggering amount of
coverage can more an issue up past another issue. This point of stagnation
may have occurred after two to three months of our study.
Local news, on the other hand, may demonstrate more flexibility in its
coverage of issues. Thus, the agenda of issues covered on local
may not stagnate as the agenda for national news might.
Overall, it should be noted that the findings here should be tempered.
Historical factors obviously could cause time-lag and memory decay
differences at any given time. As Stone and McCombs (1981) conclude, "It
cannot be assumed that a neat pattern will be established in any
specific week during which the content of the news media will yield the
same, or a highly similar, pattern of salient issues corresponding to
public agenda." The optimal time-lags and memory decay time periods
here, then, could be unique to the present study.
Regardless, the results here point to a potential fruitful area for future
research. Researchers should examine why agenda-setting effects seem to
drop off after a certain amount of time. Apparently, mental
the news may be limited by time. As Zucker (1978) concluded, old news
be forgotten. Mental processing of the news obviously is very
Overall, it is hoped that the findings here will offer future
agenda-setting researchers a guide to follow when plotting time-lags
between survey periods and media coverage. The results demonstrate that
memory decay can vary across different media, and these differences
be noted when determining time frames for agenda-setting studies.
precision in measuring time-lags and memory decay time periods is
imperative for future agenda-setting research.
Table 1. Previous studies examining the optimal time-lag for
agenda-setting effects to occur.
Researchers News media Optimal time-lag
Eaton (1989) ABC, NBC, CBS, zero to two weeks
New York Times,
Los Angeles Times,
Wall Street Journal,
Time, Newsweek, U.S.
News & World Reports
Stone and Time and four-month period
McCombs (1981) Newsweek stretching from two
to six months before
the survey period
Salwen (1988) Three largest five to seven weeks
Winter and New York Times four-to-six week
Eyal (1981) period immediately
prior to fieldwork
Zucker (1978) Three national two to six weeks
networks before the survey
Table 2. Responses to "most important problem" question.
Issue Percent naming it
number one problem
1. Crime 40.5
2. Health care 13.5
3. Economy 12.2
4. Dissatisfaction with government 6.3
5. Social problems 5.4
6. Budget deficit 5.0
7. Poverty/homelessness 4.5
8. Morality 3.6
9. Human rights 2.7
10. (t) International problems 2.3
10. (t) Drug abuse 2.3
12. AIDS 1.8
Table 7. Optimal time-lags and memory decay time periods for three news
Medium Optimal Memory decay
time-lags time periods
National network 4-5 days & 14 days &
news broadcast 62-91 days beyond 180 days
Local news 6-7 days 14 days &
broadcast 21 days
Local 15 & 18 days 28 days &
newspaper 84 days
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Memory Decay and the Agenda-Setting Effect:
An Examination of Three News Media
By Wayne Wanta
School of Journalism and Communication
1275 University of Oregon
Eugene, OR 97403-1275
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and Melissa J. Roy
School of Journalism and Communication
1275 University of Oregon
Eugene, OR 97403-1275
**Manuscript submitted to the Communication Theory & Methodology Division
for consideration of presentation at the Association for Education in
Journalism and Mass Communication annual convention, Washington, D.C.
**Wayne Wanta is an assistant professor and Melissa Roy is a graduate
student in the School of Journalism and Communication at the University
Memory Decay and the Agenda-Setting Effect:
An Examination of Three News Media
This study examined how individuals' memory of information about issues
covered in three news media decays over time. Local newscasts,
network newscasts and local newspaper coverage showed agenda-setting
effects in a relatively short time (four to eight days), but the effect
decayed shortly thereafter (14 to 28 days). The results also suggest
the agenda-setting effect is much stronger and memory decay is much
gradual for the local newspaper.