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Tobit or Not Tobit?

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  • Jay Stewart

    ()
    (U.S. Bureau of Labor Statistics)

Abstract

Time-use surveys collect very detailed information about individuals’ activities over a short period of time, typically one day. As a result, a large fraction of observations have values of zero for the time spent in many activities, even for individuals who do the activity on a regular basis. For example, it is safe to assume that all parents do at least some childcare, but a relatively large fraction report no time spent in childcare on their diary day. Because of the large number of zeros Tobit would seem to be the natural approach. However, it is important to recognize that the zeros in time-use data arise from a mismatch between the reference period of the data (the diary day) and the period of interest, which is typically much longer. Thus it is not clear that Tobit is appropriate. In this study, I examine the bias associated with alternative estimation procedures for estimating the marginal effects of covariates on time use. I begin by adapting the infrequency of purchase model, which is typically used to analyze expenditures, to time-diary data and showing that OLS estimates are unbiased. Next, using simulated data, I examine the bias associated with three procedures that are commonly used to analyze time-diary data—Tobit, the Cragg (1971) two-part model, and OLS—under a number of alternative assumptions about the data-generating process. I find that the estimated marginal effects from Tobits are biased and that the extent of the bias varies with the fraction of zero-value observations. The two-part model performs significantly better, but generates biased estimated in certain circumstances. Only OLS generates unbiased estimates in all of the simulations considered here.

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Bibliographic Info

Paper provided by U.S. Bureau of Labor Statistics in its series Working Papers with number 432.

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Length: 27 pages
Date of creation: Nov 2009
Date of revision:
Handle: RePEc:bls:wpaper:ec090100

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Keywords: Tobit; time use;

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Cited by:
  1. Shelley Pacholok & Anne Gauthier, 2010. "Non-Participant Fathers in Time-Use Studies: Uninvolved or Data Artifact?," Social Indicators Research, Springer, vol. 96(2), pages 249-266, April.
  2. Moreau, Nicolas & Stancanelli, Elena G. F., 2013. "Household Consumption at Retirement: A Regression Discontinuity Study on French Data," IZA Discussion Papers 7709, Institute for the Study of Labor (IZA).
  3. Hamermesh, Daniel S. & Trejo, Stephen, 2010. "How Do Immigrants Spend Their Time? The Process of Assimilation," IZA Discussion Papers 5010, Institute for the Study of Labor (IZA).
  4. Cawley, John & Liu, Feng, 2012. "Maternal employment and childhood obesity: A search for mechanisms in time use data," Economics & Human Biology, Elsevier, vol. 10(4), pages 352-364.
  5. Stephen B. DeLoach & Mark Kurt, 2011. "Discouraging Workers: Estimating the Impacts of Macroeconomic Shocks on the Search Intensity of the Unemployed," Working Papers 2011-01, Elon University, Department of Economics.
  6. Manan Roy & Daniel Millimet & Rusty Tchernis, 2012. "Federal nutrition programs and childhood obesity: inside the black box," Review of Economics of the Household, Springer, vol. 10(1), pages 1-38, March.
  7. Maria Gutiérrez-Domènech, 2010. "Parental employment and time with children in Spain," Review of Economics of the Household, Springer, vol. 8(3), pages 371-391, September.
  8. Nicolas Moreau & Elena Stancanelli, 2013. "Household Consumption at Retirement: A Regression Discontinuity Study on French," Documents de travail du Centre d'Economie de la Sorbonne 13072, Université Panthéon-Sorbonne (Paris 1), Centre d'Economie de la Sorbonne.
  9. repec:ese:iserwp:2006-49 is not listed on IDEAS
  10. Hans Bloemen & Elena Stancanelli, 2014. "Market hours, household work, child care, and wage rates of partners: an empirical analysis," Review of Economics of the Household, Springer, vol. 12(1), pages 51-81, March.
  11. Reich, Nora, 2012. "Fathers' childcare: The difference between participation and amount of time," HWWI Research Papers 116, Hamburg Institute of International Economics (HWWI).
  12. Stancanelli, Elena G. F. & Stratton, Leslie S., 2010. "Her Time, His Time, or the Maid's Time: An Analysis of the Demand for Domestic Work," IZA Discussion Papers 5253, Institute for the Study of Labor (IZA).
  13. Harley Frazis & Jay Stewart, 2010. "How to Think About Time-Use Data: What Inferences Can We Make About Long- and Short-Run Time Use from Time Diaries?," Working Papers 442, U.S. Bureau of Labor Statistics.
  14. J. Gimenez-Nadal & Jose Molina, 2013. "Parents’ education as a determinant of educational childcare time," Journal of Population Economics, Springer, vol. 26(2), pages 719-749, April.
  15. Daniel S. Hamermesh & Stephen J. Trejo, 2010. "How Do Immigrants Spend Time?: The Process of Assimilation," NBER Working Papers 16430, National Bureau of Economic Research, Inc.
  16. Grossbard, Shoshana & Vernon, Victoria, 2014. "Common Law Marriage and Male/Female Convergence in Labor Supply and Time Use," IZA Discussion Papers 7937, Institute for the Study of Labor (IZA).
  17. Woodward, Jonathan, 2011. "Time as an Ingredient in Meal Production and Consumption," Working Papers 11-12, University of North Carolina at Greensboro, Department of Economics.

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