respondent types.<sup>18</sup> The selected proxy then reported on up to two other randomly selected household members age 10 or older. Because in actual surveys, proxy respondents are not randomly chosen, but selected on the basis of availability, our experiment did not exactly mimic the actual conditions that result in proxy responses in household surveys.<sup>19</sup> However, it will provide estimates of proxy response bias<sup>20</sup> for a representative sample of potential proxies within the household.

The benchmark against which the commonly used approaches reflected by the short and proxy treatments are compared is the detailed self‐report questionnaire, which is generally considered “best practice”. Grosh and Glewwe (2000), providing detailed guidance to household surveys in developing countries recommend including screening questions. The use of multiple questions is also recommended by ILO as several categories of workers, including casual workers, unpaid family workers, apprentices, household members engaged in non‐market production, and workers remunerated in‐kind, have difficulties to correctly interpret a one off question about “any type of work” as referring to their situation (Hussmanns, Mehran, and Verma 1990).<sup>21</sup> The aim of this paper is to investigate whether point estimates of returns to education vary depending on the survey designs, using existing methods of analysis ‐ not necessarily to provide new or more accurate estimates of returns to education for Tanzania. The following equation provides a benchmark specification using OLS to estimate the returns to education: ln _Wi_  0  1 _Si_  2 _j_  _Si_  _Ti j_   3 _Ti j_  4 _Xi_  5 _Di_  _i_ (2) 18 The design of our survey was informed by assessing Tanzanian CWIQ 2006 data which indicated that the average Tanzanian household in this area has between two to three adults who could serve as a proxy with a minimum age of 15. Our sample households had 2.7 members 15 years and older on average.

19 An alternative research design to assess the effect of proxy respondents would have been to interview two members of the household who report on their own labor activities and proxy report on the other. We did not implement such a design because it proved to be too difficult to ensure a proper implementation for a medium to large sample. After consultation with counterparts in Tanzania, we concluded that it would be difficult to assure that proxy and self responses would be independent and would remain unaffected by the knowledge that another household member reports on the same information, given the normally social nature of this setting. The specific concern was that the design (and open communication about this design within the village) would trigger either a coordinated response by household pairs and/or accommodation of response to other’s expectations, which would introduce potentially much larger (unobserved) respondent biases.

20 If desired we can also exploit the information we have about the relationship between the proxy respondent and the individual on whom the proxy informs to assess whether there are systematic response patterns that depend on the proxy chosen. Because of small household sizes, in actuality the spouse of the head of the household was in the vast majority (77%) of cases chosen, corresponding to the usual proxy respondent in surveys. Therefore, not surprisingly, our results are similar when limiting our sample for proxy respondents to spouses only (results not reported).

21 All survey assignments received in addition to the labor module also five other modules: household roster, assets, dwelling characteristics, land, food consumption, and non‐food expenditures. The questions followed the same sequence and the same phrasing and recall periods.

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