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Comparing global questions and answers to results from 

detailed specific questions: 

Data on Food Expenditures from the Consumer

Expenditure Survey, 1998 - 2018

Steven Henderson

Consumer Expenditure Surveys Program Report Series

Overview and Summary

How do the dollar amounts collected from global questions that ask respondents to estimate their usual spending 

for a certain time period compare to answers gathered by specific questions? Are they higher or lower, or

similar? Research comparing 21 years of reports of itemized expenditures on Food at home and Food away 

from home from the Consumer Expenditure Survey (CE) Diary instrument with the responses from the global 

food questions from the CE Interview Survey show that it depends. Using detailed prepublication data from 

1998 to 2018, the aggregate dollars reported in the Diary for specific food purchases for eating at home are 

always lower than the global estimates from the Interview. The Diary to Interview ratio for this group of Food 

at home items has consistently ranged between 76 percent and 82 percent. 

Conversely, the expenditures reported for eating at restaurants and away from home collected in the Diary are 

always higher than the global estimates from the Interview survey. The range is greater, from 166 percent 

higher to 189 percent higher between 1998 and 2006, and then from 104 percent to 128 percent higher between 

2007 and 2018. There was a change in how the global question in the Interview Survey was asked in 2007 

which caused a shift in the ratios.

Results and Analysis

Table 1 shows how the reported amounts for food from the Diary compare with global estimates for food 

expenditures from the Interview survey for each year. See the Methodology section below for how the 

categories were adjusted. 

The Food at home Diary/Interview Ratio column shows that itemized purchases in the Diary are consistently 

lower than the global estimates from the Interview, ranging from 76 to 82 percent.

The Food away from home Diary/Interview Ratio column shows that respondents in the Diary always report 

higher spending on itemized meals away from home in their week of diary record keeping, compared to the 

global estimates by respondents in the Interview Survey asked to provide either a monthly or weekly estimate.
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The last column in the table shows the ratio of total aggregate dollars spent for Food at home plus Food away 

from home from the Diary compared to Food at home plus Food away from home from the Interview for 

comparable categories. Starting in 2007, the Diary combined amounts for both food categories have been 

between 86 and 94 percent of the Interview amounts. 

The table shows that using the combined global estimates for food from the Interview instead of the reported 

amounts from the Diary would exceed the reported dollars spent by U.S. Diary households on food. The positive 

dollar difference for Interview groceries is larger than the negative dollar difference for restaurant meals, and the 

differences do not cancel each other out. 

Table 1

Itemized expenditures for food from the Diary compared to Interview global estimates

comparable categories only

 Year Food at home Diary/ 

Interview Ratio

Food away from home 

Diary/Interview Ratio

Total $ Food at home plus $ 

Food away Ratio

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

78

81

81

81

80

81

82

79

78

77

78

80

77

78

78

79

77

76

76

80

79

166

172

169

185

189

178

185

192

189

104

121

122

117

121

116

117

116

119

121

128

122

 97

101

100

102

103

102

104

104

102

 86

 90

 91

 88

 90

 88

 89

 88

 89

 89

 94

 92

Why are expenditures for itemized Food at home purchases from the Diary always lower than global Interview 

responses? There are two suggested causes.

1. There is a difference in how consumers estimate their usual weekly amount compared to their actual 

itemized expenses, and the weekly estimated amount is not cognitively the same. In addition to asking 

respondents to record each food purchase, Diary respondents are asked the same global questions about 

food purchases as the respondents in the Interview Survey. Previous internal unpublished research 

using 2017 data comparing the Diary variables for itemized food totals with the global estimates showed 

that the weekly itemized total was higher than the global estimate from that same household only 39 

percent of the time – that is, just under 40 percent of the respondents said they actually spent more in 

itemized grocery spending this week than their estimate for a usual week – but was lower in 
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approximately 61 percent of the cases. Investigating these cases further, over 11 percent of all the 2017

Diary households reported zero purchases in that week’s diary. They indicated that they bought no 

groceries in that time period. However at the same time, those households responded to the global 

question that their weekly estimated grocery bill averaged $94. These zeroes lowered the published 

average for Diary food, and caused the global estimated amount to be higher than the published 

itemized amount.

2. The global estimate for Food at home is calculated as the difference between total purchases at grocery 

stores minus the purchase of non-food items, plus other purchases of food other than at grocery stores. 

Because the amount spent on food is the residual, the cause of the higher ratio may be consumers 

consistently underestimating the non-food amount of their usual weekly grocery shopping trip.

Why are itemized food away from home purchases always higher than global estimates? And what caused the 

change in the ratios from 2006 to 2007? There are two key findings.

1. When asked a global question on spending on Food away from home, respondents always 

underestimated their actual costs or perhaps the number of times they eat out over an average length of 

time compared to filling out a diary. Twenty years of data show a consistent pattern: asking for specific 

restaurant expenditures yields a higher dollar total.

2. Secondly, the longer the time period over which respondents are asked to provide an expenditure 

estimate to a global question, the more respondents under-reported their spending on Food away from 

home. From 1998 to 2006 Interview participants were asked to estimate how much per month they 

spent eating out. The Diary/Interview ratio was between 166 to 192 percent higher. 

In 2007 the global question was changed from “monthly” to “weekly.” The new question was “What 

has been your or your CU's usual WEEKLY expense for meals, or snacks from restaurants, fast food 

places, cafeterias, carryouts or other such places?” The pre-2007 question had been “What was the usual 

MONTHLY expense for these purchases?” 

The shorter reference period initially brought the ratio closer to 100 percent. Note that in 2007 the 

estimates from the Interview and Diary were almost identical – the Diary to Interview ratio was only 

four percent higher that year. Economists in the CE Production and Control Branch suggested there was 

some overlap that year in how the global question was asked; perhaps some field representatives were 

still asking for “monthly estimates” out of familiarity with the old survey question, while the computer 

system was recording the amount as weekly and then multiplying it to get monthly and quarterly 

amounts. As shown in the table, the Diary/Interview ratio then jumped to 21 percent higher in 2008 and 

has stayed between 16 and 28 percent higher each year since then.

Conclusions and Impact for Data Users

The results of this comparison are important for researchers who select data from only one survey, rather than 

using the integrated results from the Diary and Interview that are used in the published CE tables and as cost 

weights used by the Consumer Price Index. 
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These results suggest that respondents do not report the same dollar amounts when asked for global estimates 

compared to itemizing expenditures. 

Researchers should be aware of these differences when using the CE data. Analysis that only uses food 

expenditures reported in the Interview Survey will have lower totals than the Diary amount spent at restaurants, 

and will have higher totals than the Diary reported amounts spent on food for home consumption. 

Methodology and Data Used

The data used in this report come from the annual detailed prepublication tables for Integrated data, Interview 

only data, and Diary only data. In order to make direct comparisons between the Diary and Interview dollar 

amounts, the following adjustments were made. Most of the published total food expenditures in the annual 

tables come from the Diary; however a few expenditures in the integrated total are sourced from the Interview 

Survey. For the Food at home comparisons used in this research paper, the only Food at Home expenditure that 

comes from the Interview -- food for home consumption purchased on trips -- was subtracted from the total 

before calculating the ratios. For calculating the Diary-to-Interview ratios for Food away from home, the 

expenditure amounts for integrated categories that come from the Interview, i.e., board, catered affairs, meals 

during out of town trips, school lunches, and meals as pay, were subtracted from the total.

For a list of the detailed prepublication categories for all expenditures including food and their selected sources

from the Interview or Diary, see the annual “All consumer units: Annual detailed expenditure means, standard 

errors, coefficients of variation, and weekly (D) or quarterly (I) percents reporting” table.

As a historical note, these same ratios in this 1998 through 2018 data comparison have been observed since the 

CE began collecting data on a continuous basis. The first published look at the 1980-81 Interview results 

included these paragraphs:

For food-at-home expenditures, respondents in the Interview survey are asked a “global” 

question, that is, to estimate the number of trips they made to the grocery store for the 3-month 

period prior to the Interview survey, the average expenditures per trip, and how much of the 

expenditure was for nonfood items, which is then subtracted from the total. Food expenditures 

at specialty and convenience stores are added to give an estimate of food at home. In the Diary 

survey, respondents keep an itemized record of daily expenditures on food and other items. 

Food-at-home estimates from the Interview survey were about 22 percent to 23 percent higher 

than the Diary survey estimates in 1980 and 1981. 

The opposite result was obtained for expenditures for food away from home, which are also 

collected with a global question in the Interview survey. Expenditures for food away from 

home (including trips) in the Interview survey were about 4 percent lower than the Diary survey 

estimates in 1980 and about 5 percent lower in 1981.

Source: Consumer Expenditure Survey: Interview Survey, 1980-81, US Department of Labor Bureau of Labor 

Statistics April 1985 Bulletin 2225, page 8.