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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
Cancer. Author manuscript; available in PMC 2012 May 15.
Published in final edited form as:
Published online 2010 November 30. doi:  10.1002/cncr.25679
PMCID: PMC3117095
NIHMSID: NIHMS236412

Update on Mammography Trends: Comparisons of Rates in 2000, 2005, and 2008*

Abstract

BACKGROUND

Mammography screening allows early detection of breast cancer, which helps reduce mortality from breast cancer, especially in women aged 50–69. This paper updates a previous analysis of trends in mammography using newly-available data from the National Health Interview Survey (NHIS).

METHODS

We used 2008 NHIS data to update trends in rates of US women having a mammogram within the two years prior to their interview, and compared two methods of calculating rates. We especially focused on 2000, 2005, and 2008 rates for women aged ≥40, 40–49, 50–64, and ≥65, by selected socio-demographic and health care access characteristics.

RESULTS

For women aged 50–64 and ≥65, patterns were similar: rates rose rapidly from 1987 to 2000, declined, or were stable and then declined, from 2000 to 2005, and increased from 2005 to 2008. Rates for women aged 40–49 rose rapidly from 1987 to 1992, and were relatively stable through 2008. There were large increases in mammography rates among immigrants who had been in the US less than 10 years, non-Hispanic Asians, and women aged ≥65 without ambulatory care insurance.

CONCLUSIONS

Overall, mammography rates did not continue to decline between 2005 and 2008. Even so, in 2008, the percent of women aged ≥40 who had a recent mammogram fell below the Healthy People 2010 objective of 70%, met in 2000. However, women aged 50–64 exceeded the Healthy People objective in 2000, 2005 and 2008 and some groups with very low mammography rates are now catching up. These are important public health achievements.

Keywords: cancer screening, mammography, early detection of breast cancer, Healthy People objective, NHIS

INTRODUCTION

In 2005, after more than a decade of increasing use of mammography screening in the United States, the rate of mammography use declined.{Breen, 2007 15630 /id} Mammography screening detects breast cancer early and, with appropriate follow-up treatment, reduces mortality from breast cancer. The decline in rates raised the concern that mammography use, after many years of increase, was now on the decline in the US. This paper examines whether the decline continued in 2008.

The mortality benefit from mammography for average-risk women in different age groups has been the focus of ongoing discussion in the mammography literature for decades.{Fletcher, 1997 17055 /id;Miller, 1991 4373 /id;Fletcher, 1993 16823 /id;Hendrick, 1997 17056 /id;Smigel, 1993 17054 /id} We focus largely on United States Preventive Services Task Force (USPSTF) guidelines because they are based on the current best scientific evidence. USPSTF guidelines have consistently recommended routine screening for women aged 50–69 because a mortality benefit has been consistently found for this age group in clinical trials. For women aged 40–49 and women aged 70 and older (or more recently women aged 75 and older), the USPSTF guidelines have not recommended mammography routinely, but have encouraged patient-physician discussion to determine need and frequency for mammography.{U.S.Preventive Services Task Force, 2009 16825 /id;Kerlikowske, 2009 16824 /id} While relative risk of breast cancer for women aged 40–49 is about the same as for women aged 50–69, mammograms are not as accurate in younger women because, in general, younger women have denser breast tissue (more glandular, less fat). Breast tissue becomes less dense as women age, especially after menopause which on average occurs around age 50.

This difference in breast density leads to differences by age in the amount of breast cancer cases detected with mammography. Data pooled from clinical trials for the USPSTF analysis conducted for the most recently released mammography guidelines showed that the number of women needed to be invited to screening to prevent one cancer death was 1904 for women aged 39–49, 1339 for women aged 50–59, and 377 for women 60–69.{Nelson, 2009 17065 /id} A metaanalysis by Hendrick et al found a mortality benefit for women 40–49 only in clinical trials that had followed subjects for more than 10 years; the benefit was found only after the women had reached their 50s {16823}. Lack of recommendation for mass screening for older women has led to further inquiry,{Mandelblatt, 2003 13701 /id} but it has not led to controversy as it has for women aged 40–49.

DATA AND METHODS

We analyzed data from the National Health Interview Survey (NHIS), a large-scale household interview survey of a statistically representative sample of the US civilian non-institutionalized population (http://www.cdc.gov/nchs/nhis.htm). The NHIS in-person interviews yield demographic and health data for all members of each participating family, and additional questions are asked about a randomly selected child (the “sample child”) and a randomly selected adult (the “sample adult”) in each family.

In the 2000, 2003, 2005, and 2008 NHIS (and in the 2010 NHIS, which was in the field at the time of writing), female sample adults aged 30 and older were asked, "Have you EVER HAD a mammogram?" Women who responded affirmatively were asked additional questions to determine the date of or time since their last mammogram. Three different formats were available for reporting that information so as to maximize the amount and precision of information obtained.

In the 2000 and 2003 NHIS, the questioning was as follows: "When did you have your MOST RECENT mammogram?" Respondents could answer using either Format 1 or Format 2:

  • Format 1. Respondents were asked to provide the DATE (month and year) of their last mammogram.
    • --
      If the year was provided, this sequence of questions was ended, whether or not the month was provided.
    • --
      If the year was not provided, questioning went on to use Format 3.
  • Format 2. Respondents were asked to provide the NUMBER OF TIME UNITS since their last mammogram (in days ago, weeks ago, months ago, or years ago).
    • --
      If the number of time units was not provided, questioning went on to use Format 3.
  • Format 3. Respondents were asked to identify the TIME INTERVAL since their last mammogram (≤1 year ago, >1 year but ≤2 years ago, >2 years but ≤3 years ago, >3 years but ≤5 years ago, or >5 years ago).

In 2005 and later, extra questioning using Format 3 was added in some cases so as to obtain extra information:

  • --
    If Format 1 was used, and the month was not reported, questioning went on to use Format 3.
  • --
    If Format 2 was used, and the answer was reported in numbers of years ago, then questioning went on to use Format 3.

The following two methods were used in the present analysis to calculate rates of women having mammograms in the last 2 years:

  • Method I, which may be used for all data years, ignores any extra information resulting from questionnaire changes made starting in 2005, in the interest of using the same computational procedures across years. Also, if the year but not the month of the last mammogram was provided using Format 1, the month is imputed to be July.
  • Method II (used for 2005 and later): If Format 3 was used, use the resulting information to calculate rates, in the interest of using the most precise information available in each year.

Breen et al.{Breen, 2007 15630 /id} compared mammography rates in 2000 to mammography rates in 2005, using Method I for 2000 data and Method II for 2005 data.

To study temporal changes in mammography use in the US, we analyzed NHIS mammography data, which were available in 1987, 1992, 1998, 2000, 2003, 2005, and 2008. The 2008 estimates are being presented for the first time. We focused on patterns and changes in mammography rates over the years 2000, 2005, and 2008, using and comparing the two methods. For more information about use of the two methods, see:

We defined “recent” mammograms as mammograms received within the last two years. We calculated rates of women having recent mammograms in years 2000, 2005, and 2008 for four age groups (≥40, 40–49, 50–64, and ≥65) and by selected demographic, socioeconomic, and health care utilization characteristics (see list of characteristics in tables). These same characteristics were presented in Breen et al.{Breen, 2007 15630 /id} along with the rationale for choosing them.

To calculate family income as a percentage of the poverty level, family income values were imputed to replace unreported income values.{Schenker, 2006 17057 /id} This accounts for differences between sample sizes for mammography rates by poverty ratio in Breen et al.{Breen, 2007 15630 /id} (in which rates were calculated using only reported income values) and sample sizes in the present analysis. Both race/ethnicity and race irrespective of ethnicity are presented.

Slight differences between 2005 sample sizes in Breen et al.{Breen, 2007 15630 /id} using Method II and 2005 sample sizes in the present paper using Method II are due to deletion of 3 observations in the latter for minor technical reasons.

RESULTS

Figure 1 displays age-specific recent mammography rates in years between 1987 and 2008 for which NHIS mammography data are available, for four age groups (and Tables 1 and and22 provide those rates for 2000, 2005, and 2008). Confidence intervals are shown as vertical lines through the points. For women aged 50–64 and ≥65, patterns were very similar: rates rose rapidly from 1987 to 2000, declined, or were stable and then declined, from 2000 to 2005, and increased from 2005 to 2008. Rates for women aged 40–49 rose rapidly from 1987 to 1992, and were relatively stable through 2008. For all women aged ≥40 combined, rates declined from 2003 to 2005, and rose from 2005 to 2008. The only age group whose rates declined between 2005 and 2008 was women aged 40–49 years.

Table 1
Percent of women aged ≥40 who had a mammogram within the last two years, for selected characteristics, National Health Interview Survey 2000, 2005, and 2008, using Method I for all years
Table 2
Percent of women aged ≥40 who had a mammogram within the last two years, for selected characteristics, National Health Interview Survey 2005 and 2008, using Method I for 2000, and Method II for 2005 and 2008

Table 1 presents age-standardized recent mammography rates for women aged ≥40 in 2000, 2005, and 2008, for selected demographic socio-economic and health care access characteristics. All estimates were calculated using Method 1, i.e., using the same computational method for all three survey years. From 2005 to 2008, the overall rate did not change significantly. Significant changes over that time period were experienced by only six of the subgroups; mammography rates rose for three subgroups and fell for three others. Declines occurred among women with family incomes of 200%–299% of the federal poverty level (FPL), who experienced a five percentage point decline in rates, and among American Indian and Alaska Native (AIAN) women, regardless of whether race/ethnicity or race alone was used to categorize them. Rates among non-Hispanic AIAN women dropped by almost 24 percentage points, and rates among all AIAN women dropped by 18 percentage points. Rates increased by about eight percentage points for women aged 64 or less with public health insurance only. They increased by almost 12 percentage points for Asian women; whether race/ethnicity or race alone was used to measure Asian-Americans, this finding was consistent.

Table 1 also compares mammography rates in 2000, when rates for ages 50+ peaked after years of increasing (see Figure 1), to rates in 2008. Overall mammography rates did not change significantly from 2000 to 2008. Seven subgroups experienced declines in mammography rates, and three had increases. Women aged 50–64 had declines of about three percentage points. Declines of a similar size were noted for women with family incomes of ≥500% of the FPL; for women aged less than 65 with private, non-HMO health insurance; for non-Hispanic white women; and for white women. Rates for women born in the US, and for women who had seen or talked to a physician in the past 12 months declined by two percentage points. Women in three smaller subgroups experienced increases in mammography use. Among women aged ≥65, most of whom are covered by Medicare, mammography use rose by 28 percentage points for the small group (unweighted sample sizes = 50 in 2000 and 31 in 2008) without insurance or with Medicare Part A only. Rates rose by nearly 10 percentage points for non-Hispanic Asians, and by 16 percentage points among immigrants who had lived in the US for less than 10 years.

Table 2 shows age-standardized rates for the same ages and characteristics as in Table 1. However, results in Table 2 were calculated using Method II for 2005 and 2008, i.e., using the most possible available information each of the three years. Table 2 replicates the comparisons of 2000 to 2005 as reported in Breen et al.{Breen, 2007 15630 /id}

It is noteworthy that results were consistent between the two tables, in the sense that whenever a difference in one table was significant, the corresponding difference in the other table, whether significant or not, was in the same direction. For example, the overall mammography rates in Table 2 declined significantly by 3.7 percentage points from 2000 to 2005 and declined significantly by 3.2 percentage points from 2000 to 2008; the respective changes in Table 1 were a significant decline of 1.8 percentage points and an insignificant decline. Also, Table 2 shows more significant differences than Table 1; e.g., Table 2 shows 17 significant decreases among the subgroups from 2000 to 2005 and 13 significant decreases from 2000 to 2008, whereas Table 1 shows only 9 and 7 decreases, respectively.

CONCLUSIONS

Whether mammography rates had peaked and would subsequently fall was a concern when a decline in rates was discovered in the 2005 data. We assessed trends in mammography rates using recently released 2008 NHIS data. To do this, we used two analytic methods and compared them. We would use Method 2 in the future, because we prefer to use the most information available and the most precise information available. But for this paper, we did not want our new conclusions about changes over time to be confounded by changes in the analytic methods used, so we looked at results of both methods. The 2008 NHIS data indicate that overall, using either method, with exceptions for some subgroups, mammography rates did not continue to decline between 2005 and 2008. Even so, the 2008 recent mammography rates for women aged ≥40 were below the Healthy People 2010 objective of 70% that was met when mammography rates peaked in 2000.

The re-analysis of trends in mammography rates attenuated the drop previously reported between 2000 and 2005, and declines previously reported for some subgroups of women became insignificant. However, both methods also showed a significant decline in mammography use among women aged 50–64 between 2000 and 2008.

Mammography use for women aged 40–49 years has been relatively stable since 1992 despite periodic controversy in the literature{Berry, 1998 11965 /id;Elmore, 2007 15557 /id} that made print-news headlines from time to time{Kolata, 1997 17058 /id;Winger, 2009 17059 /id}; the more relaxed guidelines for women ages 40–49 may help explain the stability of lower rates of mammography use in this age group.

It may be surprising to some that mammography rates declined by at least three percentage points between 2000 and 2008 for women aged 40–64 with private non-HMO health insurance, while they increased or were stable for private HMO insurance. However, prevailing evidence suggests that HMOs provide better cancer screening coverage{Klabunde, 2004 13758 /id;Makuc, 1994 6810 /id} and treatment.{Shavers, 2002 12908 /id}

Logistic diffusion theory posits that people adopt new ideas or techniques in an ordered sequence. The rate of adoption over time in a social system can be displayed as an S-shaped cumulative curve.{Breen, 1997 9407 /id;Rogers, 1971 4228 /id} Historically, women with health insurance, a usual source of care, and higher incomes and educational attainments have been early adopters of mammography.{Breen, 1994 4694 /id} Between 2000 and 2008, mammography use dropped about three percentage points among those who had been early adopters of mammography, including women in the categories ages 50–64, family income ≥500% of FPL, private non-HMO insurance for women aged 40–64, and white race. Also surprising was a two percentage point drop for women born in the US and for women who had contact with a general physician in the past year. A leading hypothesis for the drop in mammography use is that some women who had visited their doctor for hormone therapy (HT) prescriptions, which led to mammography referrals, stopped these visits when evidence showed an increased risk of breast cancer associated with HT.{Borrayo, 2009 16746 /id;Hersh, 2004 16705 /id;Buist, 2004 16704 /id} It will be useful to have data from the 2010 cancer supplement on the NHIS to learn more about use of mammography among these early adopters of mammography.

The few increases in mammography use between 2000 and 2008 are worth noting because they were all 10 percentage points or more. Mammography rates rose among immigrants who had been in the US less than 10 years and among non-Hispanic Asians. There was also an increase among women aged ≥65 who were uninsured or who had Medicare Part A only. While these groups comprise small portions of the US population, their initial rates were low and their increases were all large (10+ percentage points). Moreover, increases in these groups may be particularly important because evidence suggests that the major reason women are diagnosed with late-stage breast cancer is that they have never been screened.{Taplin, 2004 15966 /id} Therefore, increasing rates of screening among populations with very low rates is estimated to have larger benefits than increasing frequency of screening among those regularly screened.{Mandelblatt, 2009 16839 /id}

Public debate over the value of mammography in women ages 40–49 may or may not translate into reduced rates. We found that rates of mammography use in women aged 40–49 have been stable since 2000 at about 64%. Rates of mammography use in women aged 65 and older have also been stable since 2000, but at a higher level—about 67%. Whether the new mammography guidelines will affect future use remains to be seen.

In conclusion, mammography use has increased by large magnitudes in several small groups with growing populations and has declined by a small amount in large groups that historically have been early adopters. Recent changes in guidelines also may affect utilization. If women and their physicians—and health care insurance companies—apply the new guidelines, it would lead to a decline in use among women aged 40–49 and an increase in use among women aged 70–74. In terms of their distribution in the US civilian noninstitutionalized population of all women aged ≥40, women are divided roughly equally among the age groups 40–49 (31% in 2008), 50–64 (39%), and ≥65 (30%). This makes it difficult to predict the direction that mammography will take in the future. We look forward to the 2010 NHIS estimates, which will permit us to observe the direction that mammography utilization will take.

ACKNOWLEDGMENT

The authors thank Timothy McNeel of Information Management Services, Inc. for expert consultation on programming and help with updating figures and tables. We thank Penny Randall-Levy for expert assistance with references. We also thank Rachel Ballard-Barbash for providing a very helpful review of the MS.

Footnotes

There are no financial disclosures from any authors

*The findings and conclusions in this paper are those of the authors and do not necessarily represent the views of the National Cancer Institute, NIH or the National Center for Health Statistics, CDC.

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