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Comments on: “Network Effects and the Educational Attainment of Young Immigrants” by Florian Hoffmann. Gustavo Bobonis ECO4060. Summary. Question: Are there neighborhood-based peer effects for immigrants Interesting question: concern with rate of assimilation

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Comments on network effects and the educational attainment of young immigrants by florian hoffmann

Comments on:“Network Effects and the Educational Attainment of Young Immigrants”by Florian Hoffmann

Gustavo Bobonis



  • Question: Are there neighborhood-based peer effects for immigrants

    • Interesting question: concern with rate of assimilation

      (Huntington, 2004; McKinnon and Parent, 2005)

    • Contribution: ID strategy that improves upon BLM to control for OVB

      • Group-region-cohort variation

    • Results: modest network effects

      • Moving from a location with no ‘peers’ to the average relative ‘share’ of peers increases individuals’ school attainment by 0.11-0.23 years (= α*3.06*12.4)

  • Distinction from previous literature: evidence of selection (movers vs. non-movers)

  • My comments: empirical framework, data & samples, potential threats to validity, discussion of results

Empirical framework and lit review
Empirical Framework and Lit Review

  • Manski (1993) – “The Reflection Problem”

    • Simultaneity problem: person A’s actions affect person B’s actions and vice versa.

    • Distinct from:

      • Correlated unobservables (e.g., common environmental shocks)

      • Endogenous group membership (e.g., selection into networks)

    • Endogenous and exogenous interactions cannot be identified, but can identify evidence of some type of peer or network effect

    • How to interpret BLM-model network effect α?

  • Reference: Moffitt (2001) – ID best-response function

    • Experimentally altering group membership

    • Partial population experiments – portion of individuals within a group are directly treated

Data samples and reference groups
Data, Samples, and Reference Groups

  • Immigrants who speak their mother tongue at home

    • Mother tongue is important determinant of ethnic identity (Alba, 1990)

    • Endogenous? Sample selection based on an action affected by network effects (“pressures to conform or to distinguish oneself”)?

    • Recommendation: Use sample of all immigrants & use indicator for non-English language spoken at home as dep. variable. ‘Network’ effect on language use?

  • Immigrants who arrived when young or U.S. born (2nd/3rd generation?)

    • U.S. born (2nd or 3rd generation) might have different reference groups

    • Recommendation: Use only 1st generation immigrants?

  • Density and ‘quality’ of other groups do not affect schooling decision?

    • e.g., “conformity” or “need of differentiation” from natives/other migrants?

    • May bias estimates of α? Depends on:

      Cov(cajk, cal,k) <, >, or = 0, for each l ≠ j

      αl network effect of other groups

      * Group all Spanish-speakers and French-speakers together?

Potential threats to validity
Potential Threats to Validity

  • Focus on “group-region-cohort” variation ID strategy:

  • What are some of the main identifying assumptions? Examples:

    • μjt = 0 (no shocks to MSAs that affect own and peers’ school attainment or

      migration into or out of MSA; e.g., MSA ‘business or political cycles’)

    • μkt = 0 (no shocks to language groups that affect own and peers’ school attainment;

      e.g., changes in group-specific tastes)

      You can include both μjt and μkt fixed effects.

    • μjkt = 0 (no shocks to environment of language groups in particular MSAs that affect

      own and peers’ school attainment)

      Example: political economy-based hypothesis

    • Individuals in language groups with relatively high share of population and (high or low) education levels demand more access to or quality of public schools

    • Affects both own and peer school achievement?

    • Mechanism may be more important for high school

    • Interpretation of reduced-form coefficient, might include a school quality mechanism

Discussion of results
Discussion of Results

  • How do we know whether α is ‘economically’ (or sociologically?) significant?

    • One std. deviation increase in cajk for a given mean school attainment level?

    • Compare to previous estimates of network effects?

  • Main estimates of α from group-region-cohort variation (Table 7):

    • Are stable around: [0.002 (0.002) – 0.006 (0.003)]

    • Probably cannot reject that they’re significantly different

    • Effect for non-movers is 0.003 (0.002) (less selection for this group?)

  • Parental background variable subgroup:

    • Estimate is -0.004 (0.003)

    • But, parental background for sub-sample of individuals living with parents.

      Self-selected sample?

    • What is main network effect estimate for sub-sample when you

      exclude parental background control?