Hirsch, Barry T

Winters, John V

English

Georgia State University

Georgia State University 
ScholarWorks @ Georgia State University 
UWRG Working Papers Usery Workplace Research Group 
8-3-2016 
Rotation Group Bias in Measures of Multiple Job Holding 
Barry T. Hirsch 
Georgia State University, bhirsch@gsu.edu 
John V. Winters 
Oklahoma State University, jvwinte@okstate.edu 
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Recommended Citation 
Hirsch, Barry T. and Winters, John V., "Rotation Group Bias in Measures of Multiple Job Holding" (2016). 
UWRG Working Papers. 95. 
https://scholarworks.gsu.edu/uwrg_workingpapers/95 
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W. J. Usery Workplace Research Group Paper Series 
 
 
 
 
Working Paper 2016-8-3 
August 2016 
 
 
 
 
 
 
 
Rotation Group Bias in Measures of 
Multiple Job Holding  
 
 
 
 
 
 
Barry T. Hirsch 
   
Georgia State University and IZA 
 
John V. Winters 
  
Oklahoma State University and IZA 
 
 
 
 
 
 
 
 
This paper can be downloaded at: http://uwrg.gsu.edu 
 
 
 
 
 
 
ANDREW YOUNG SCHOOL 
 
O F  P O L I C Y  S T U D I E S 
  
 
 
 
 
 
 
 
Rotation Group Bias in Measures of Multiple Job Holding  
 
 
Barry T. Hirsch and John V. Winters 
 
 
August 2016 
 
Forthcoming, Economics Letters 
 
 
Abstract 
 
 
Reported multiple job holding rates in the U.S. are found to be substantially higher among workers in their 
first month in the CPS sample (the first rotation group), with rates declining in subsequent rotation groups. 
True rates should not differ across rotation groups. Using 22 years of CPS data, multiple job holding rates 
based solely on the first rotation group were 27.5 percent higher than official rates based on all rotation 
groups. Rotation group bias worsened over time and could account for as much as one-quarter of the 
measured decline in multiple job holding.  
 
 
Keywords: Multiple job holding, rotation group bias, Current Population Survey 
 
JEL code:  J21 (labor force and employment) 
 
Hirsch [contact author]: Department of Economics, Andrew Young School of Policy Studies, Georgia State 
University, Atlanta, Georgia 30302-3992, and IZA (Bonn). Email: bhirsch@gsu.edu.  
 
Winters: Department of Economics, Oklahoma State University, Stillwater, OK 74078-4011, and IZA 
(Bonn). Email: jvwinte@okstate.edu.  
 
1 
 
1. Introduction  
The monthly Current Population Survey (CPS) is a key source for U.S. labor statistics, most notably 
the monthly unemployment and labor force participation rates. Residences and their occupant households are 
surveyed over eight ‘month-in-sample’ periods (i.e., MIS or rotation group). A residence is surveyed over four 
consecutive months, followed by eight months out of the survey, followed by four additional months (e.g., 
MIS 1-4 in April-July 2014; MIS 5-8 in April-July 2015).
1
 There is no reason to expect true labor force 
outcomes to differ with respect to MIS, yet Krueger, Mas, and Niu (KMN forthcoming) show that U.S. 
unemployment rates are highest in MIS 1, declining in MIS 2-4, rising in MIS 5, and declining again in MIS 6-
8. ‘Rotation group bias’ (RGB) in the unemployment rate was noted previously (Hall 1973, Bailar 1975, Solon 
1986), but was not widely known to researchers or analyzed in depth prior to KMN. The authors do not argue 
that RGB is universal; they find no evidence for RGB in unemployment in the Canadian labor force survey. 
In this note, we show that another official employment measure compiled from the CPS, the multiple 
job holding (MJH) rate, exhibits substantial rotation group bias. Multiple job holding provides opportunities 
for individuals and households to increase incomes and lower risk, to acquire a broader portfolio of human 
capital, and, in some cases, increase job satisfaction. Secondary jobs tend to be short-term; hence, MJH rates 
at a point in time greatly understate the proportion of workers who have held multiple jobs within the past 
year or at some point in the past.
2
 The Bureau of Labor Statistics (BLS) and the Census Bureau began 
measuring multiple job holding on a regular monthly basis following a major overhaul of the CPS in January 
1994. Using an index suggested by KMN, we show that MJH rates in the first rotation group (MIS 1) are 21 
percent larger than the rate using all rotation groups in 1994-95; the difference in 2014-2015 is 33 percent. 
This rotation group bias for multiple job holding is substantially higher than the 9 percent level found for 
unemployment by KMN over the 1994-2014 period (KMN, forthcoming, Table 2).
3
 Because rotation group 
bias is substantial and worsened over time, it is likely that the true MJH rate is higher than the official rate 
and that measured decline in MJH is overstated. We document these patterns below. 
2. Data and Analysis 
Multiple job holding was measured on a regular basis beginning in January 1994 following the major 
redesign of the CPS. All employed individuals ages 16+ are asked the question: “Last week, did you have 
more than one job (or business), including part-time, evening, or weekend work?” The Bureau of Labor 
Statistics (BLS) defines a multiple job holder as an individual who: (a) holds wage and salary jobs with two 
or more employers; (b) combines a wage and salary job with self-employment; or (c) combines a wage and 
                                                          
1
 The first and fifth rotation groups require (with some exceptions) that a Census field representative conducts the 
household survey in person. For MIS 2-4 and 6-8, most surveys are conducted over the phone rather than in person. 
2
 For references to the larger literature on multiple job holding, see Lalé (2015) and Hirsch, Husain, and Winters (2016). 
3
 The unemployment rate is of course a more important measure of economic performance than is the MJH rate. 
2 
 
salary job with one as an unpaid family worker. In this paper, we use the same data and methodology as 
BLS, including all rotation groups of the CPS from January 1994 through December 2015 (22 years). The 
combined sample size for years 1994-2015 is 16,736,173, an average 760,735 workers per year. 
Following BLS procedures, Figures 1a and 1b show annual MJH rates (diamonds) for men and 
women based on all CPS rotation groups, respectively, from 1994-2015. Men’s rates fell from an average 
6.2% in 1994-95 to 4.5% in 2014-15; women’s rates fell from 6.2% to 5.3% over the same period (the 
combined rates fell from 6.2% to 4.9%). Also included in the figures are MJH rates compiled separately for  
 
 
3.5%
4.0%
4.5%
5.0%
5.5%
6.0%
6.5%
7.0%
7.5%
8.0%
8.5%
1994 1997 2000 2003 2006 2009 2012 2015
Figure 1a: Male Multiple Job Holding Rates by Year for All, 
MIS 1, MIS 5, MIS 2-4 & 6-8 
All Men MIS_1 MIS_2-4 & 6-8 MIS_5
3.5%
4.0%
4.5%
5.0%
5.5%
6.0%
6.5%
7.0%
7.5%
8.0%
8.5%
1994 1997 2000 2003 2006 2009 2012 2015
Figure 1b: Female Multiple Job Holding Rates by Year 
for All, MIS 1, MIS 5, MIS 2-4 & 6-8 
All Women MIS_1 MIS_2-4 & 6-8 MIS_5
3 
 
MIS 1 (squares), MIS-5 (crosses) and from the remaining six (MIS 2-4 & 6-8, triangles). Clearly evident is 
that individuals report substantially higher rates of MJH in their first month in the survey than in subsequent 
months. The official rate is substantially lower than the MJH rate reported by workers in MIS 1, modestly 
lower than for those in MIS 5, and higher than the average for the remaining six rotation groups. 
Figure 2 provides summary evidence of differences in reported MJH rates by rotation group based on 
the average across 22 years, showing overall MJH rates and those for men and women. Focusing on combined 
male and female rates, MJH for those in MIS 1 averages 6.9%, as compared to only 4.9% for MIS 8 (and 5.2% 
for MIS 2 through MIS 8). The ‘tilted-W’ pattern seen in Figure 2 mimics that seen for the unemployment rate 
(KMN forthcoming), although rotation group bias is more extreme for MJH than for unemployment.  
Figure 2: Mean Multiple Job Holding Rates by Rotation Group and Gender, 1994-2015 
 
We draw three general takeaways from the evidence. First, households appear to provide more 
comprehensive labor market information when surveys are conducted in person, hence the peaks at MIS 1 
and MIS 5. Second, lower MJH is reported the longer a household is in the survey, seen by the downward 
slope as one moves from earlier to later rotation groups.
4
 And third, rotation group differences are somewhat 
higher among men, the ratio of MIS 1 to MIS 8 rates being 1.44 for men and 1.39 for women. Although we 
find evidence of severe rotation group bias in multiple job holding, we cannot know whether reports in MIS 
                                                          
4
 An important implication of rotation group bias and declines in MJH or unemployment reporting by month-in-sample is 
that transitions out of (into) MJH or unemployment are overstated (understated). Lalé (2015) documents reported MJH 
transitions seen in monthly pairs of the CPS. Numerous papers have examined unemployment transitions. 
4.0%
4.5%
5.0%
5.5%
6.0%
6.5%
7.0%
7.5%
1 2 3 4 5 6 7 8
CPS Rotation Group Month-in-Sample  
All
Men
Women
4 
 
1 (or any other month in sample) provide an unbiased (or least biased) measure of MJH. Our expectation is 
that households are the most engaged in the survey during the first MIS and provide the most accurate 
information in that month. We cannot rule out, however, the possibility that in the first month respondents 
“telescope” and recall earlier MJH that they incorrectly report as occurring the prior week. Moreover, some 
respondents may overreport activities due to a (misplaced) desire to please a Census field representative, 
although this motive would apply to some degree for all months in sample. 
There is widespread belief by economic pundits and many economists that the U.S. labor market is 
producing an increasing number of short-term, flexible “gig” jobs, but that such changes are difficult to discern 
in official government statistics (see Abraham et al. 2016; Katz and Krueger 2016). Multiple jobs are often 
short-term jobs, but official MJH rates have declined rather than increased over time. Might some of the 
decline seen in MJH, in particular among men, be the result of rotation group bias? The short answer is yes, 
but not by much. Table 1 provides average MJH rates, overall and by gender, for 1994-5 and 2014-15. Over 
this 20 year period, the nationwide MJH rate declined by 1.28 percentage points, from 6.17 to 4.88 percent. 
Percentage point declines for MIS 2 through MIS 8 ranged from 1.25 to 1.44, whereas the decline in MIS 1 
was only 0.99. Comparing the 0.99 MIS 1 percentage point decline to the 1.28 decline seen overall, the 
suggestion is that decline in MJH may be overstated by as much as 29 percent (1.28/0.99) or, equivalently, 23 
percent of the apparent decline reflects rotation group bias (1 – 0.99/1.28). This conclusion relies on the 
assumption that rates reported in MIS 1 are accurate and those in MIS 2-8 are not, or alternatively, that 
changes in MIS 1 rates over time are accurate but those in MIS 2-8 are not. In short, rotation group bias causes 
MJH decline to be overstated; it does not reverse the finding that MJH has declined. 
3. Conclusion and Implications 
This note demonstrates that there exists strong rotation group bias in reporting of multiple job 
holding. Space does not permit us to explore in depth why MJH reporting declines with months spent in the 
survey. KMN thoroughly examine explanations for rotation group bias in measuring unemployment, and rule 
out most of these. Two conclusions appear justified. First, households are more engaged and provide fuller 
information during MIS 1 and 5, interviews (mostly) conducted in person rather than by phone. In drawing 
this conclusion we downplay the likelihood of telescoping. Second, continuing declines in MJH (and 
unemployment) rates in the survey months following MIS 1 and 5 suggest that households become less 
engaged and less likely to report some labor market activities. Consistent with this interpretation, KMN 
emphasize that increases in rotation group bias occurred over periods in which we have seen increases in 
survey and item (e.g., earnings) nonresponse.  
We examined two possible explanations for rotation group bias in MJH. First, we speculated that as 
time in the survey increases, decreased willingness to report dual jobs might be concentrated among those 
5 
 
with second jobs requiring relatively few hours. If that were the case, we should see higher mean hours 
worked on secondary jobs in later rotation groups displaying low rates of MJH. No such pattern is found. 
Mean hours on both secondary jobs and the primary job are highly similar across all rotation groups. Second, 
we examined MJH differences between self-respondents and those whose labor market responses are 
provided by a proxy (another household member, frequently a spouse). Reported MJH rates are substantively 
higher in the self-respondent than in the proxy respondent sample; however, the pattern of rotation group bias 
was nearly identical for both (KMN provide similar evidence for unemployment).  
Evidence that rotation group bias affects the quality of labor market measures suggests the need for 
further study and experimentation. The Census Bureau (and outside researchers) might study and document 
the degree of rotation group bias seen in widely-used labor market measures. Census can experiment with 
alternative survey methods and determine whether there exist cost-justified changes. If rotation group bias is 
omnipresent, one can consider whether a switch to in-person surveys in all months-in-sample reduces 
rotation group bias sufficiently so to warrant the higher costs. Census also could alter survey methods for 
specific measures deemed problematic. Multiple job holding, for example, falls off sharply following the first 
and fifth months in survey. In MIS 2-4 and MIS 6-8 individuals could be reminded if they reported 2 or more 
jobs in the prior month, and then asked if they continue to work at multiple jobs.
5
 
References 
Abraham, Katherine G., John Haltiwanger, Kristin Sandusky, and James R. Spletzer. 2016. Measuring the 
‘gig’ economy. Paper presented at the Society of Labor Economists Annual Meetings, May.  
Bailar, Barbara A. 1975. The effects of rotation group bias on estimates from panel surveys. Journal of the 
American Statistical Association 70, no. 349: 23-30. 
Hall, Robert E. 1970. Why is the unemployment rate so high at full employment? Brookings Papers on 
Economic Activity? 70, no. 3:369–410. 
Hirsch, Barry T., Muhammad M. Husain, and John V. Winters. 2016. Multiple job holding, local labor 
markets, and the business cycle. IZA Journal of Labor Economics 5, no. 4: 1–29. 
Katz, Lawrence F., and Alan B. Krueger. 2016. The rise and nature of alternative work arrangements in the 
United States, 1995-2015, unpublished manuscript, March. 
Krueger, Alan B., Alexandre Mas, and Xiaotong Niu. forthcoming. The evolution of rotation group bias: Will 
the real unemployment rate please stand up? Review of Economics and Statistics. 
Lalé, Etienne. 2015. Multiple jobholding over the past two decades. Monthly Labor Review, April.  
Solon, Gary, 1986. Effects of rotation group bias on estimation of unemployment. Journal of Business & 
Economic Statistics 4, no. 1: 105-109. 
  
                                                          
5
 Beginning in 1994, Census adopted this “dependent interviewing” approach for the primary job (and other activities), 
stating to the respondent what specific job was reported the previous month and then asking if the worker is currently in 
that same job.  
6 
 
Table 1: Weighted MJH Means by Month-in-Sample, 1994-95 and 2014-15 
 
1994-95 
 
2014-15 
 
  N 
MJH 
rate 
KMN 
Index   N 
MJH 
rate 
KMN 
Index 
∆MJH 
rate 
All 1,561,602 6.17% 100.0 
 
1,480,008 4.88% 100.0 -1.28 
MIS 1 193,761 7.46% 121.0 
 
184,403 6.47% 132.6 -0.99 
MIS 2 197,971 6.31% 102.3 
 
187,328 5.05% 103.5 -1.25 
MIS 3 197,394 6.02% 97.6 
 
187,285 4.70% 96.2 -1.32 
MIS 4 196,119 5.96% 96.6 
 
186,300 4.52% 92.5 -1.44 
MIS 5 191,952 6.51% 105.6 
 
181,069 5.08% 104.1 -1.43 
MIS 6 194,576 5.81% 94.3 
 
183,543 4.53% 92.8 -1.28 
MIS 7 194,926 5.69% 92.2 
 
184,251 4.40% 93.8 -1.28 
MIS 8 194,903 5.55% 90.1   185,829 4.25% 87.1 -1.30 
Men 823,038 6.17% 100.0 
 
771,982 4.52% 100.0 -1.65 
MIS 1 101,968 7.57% 122.7 
 
96,051 6.12% 135.4 -1.45 
MIS 2 104,353 6.29% 102.0 
 
97,580 4.66% 103.2 -1.63 
MIS 3 104,096 5.97% 96.8 
 
97,564 4.34% 96.0 -1.64 
MIS 4 103,372 5.95% 96.4 
 
97,254 4.14% 91.7 -1.81 
MIS 5 101,151 6.53% 105.8 
 
94,458 4.75% 105.3 -1.77 
MIS 6 102,592 5.82% 94.3 
 
95,781 4.16% 92.1 -1.66 
MIS 7 102,769 5.68% 92.0 
 
96,221 4.02% 92.6 -1.66 
MIS 8 102,737 5.54% 89.8   97,073 3.90% 86.3 -1.65 
Women 738,564 6.16% 100.0 
 
708,026 5.30% 100.0 -0.86 
MIS 1 91,793 7.33% 119.0 
 
88,352 6.88% 129.9 -0.46 
MIS 2 93,618 6.32% 102.6 
 
89,748 5.49% 103.7 -0.83 
MIS 3 93,298 6.07% 98.5 
 
89,721 5.10% 96.4 -0.96 
MIS 4 92,747 5.97% 97.0 
 
89,046 4.94% 93.3 -1.03 
MIS 5 90,801 6.49% 105.3 
 
86,611 5.45% 102.9 -1.04 
MIS 6 91,984 5.81% 94.4 
 
87,762 4.96% 93.6 -0.86 
MIS 7 92,157 5.70% 92.5 
 
88,030 4.84% 94.9 -0.86 
MIS 8 92,166 5.57% 90.4   88,756 4.65% 87.9 -0.91 
KMN Index is the ratio of the MJH rate for each MIS, divided by the all-MIS rate. 
Source: Monthly Current Population Surveys, January 1994 - December 2015. 
   


Rotation Group Bias in Measures of Multiple Job Holding

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Rotation Group Bias in Measures of Multiple Job Holding

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