Keywords
Height premium, child height, adult height, economic models
Height premium, child height, adult height, economic models
Adult height has been found to be correlated with labor-market wages across various settings1–3. In high-income settings, a contribution to this association has been hypothesized to be due to status, prestige and self- and social-esteem which may be associated with taller stature4. Further in some settings, this connection has been hypothesized also to be due to physical strength and more robust health accompanying taller stature, which is favorable for manual and agrarian labor5. Adult height is also the culmination of nutritional exposures and growth from conception through adulthood1,6. Linear growth faltering in childhood has many environmental and nutritional determinants that may also be associated with developmental outcomes, such as cognitive, language and motor abilities7,8. Further, environmental conditions in childhood affect the timing of growth and the onset of the adolescent growth spurt, with children from higher socioeconomic classes achieving adult height at earlier ages. While children from less-advantaged backgrounds can experience an extended growth period, on average this does not negate adult height deficits that originate earlier in childhood1,6,9. This evidence suggests that the relationship between adult height and wages is complex, and may be associated with and mediated by many different pathways.
There is a substantial economic literature examining the relationship between adult height and wages, also known as the “height premium” (HP), in different settings. A recent review summarized that a 1-cm increase in adult stature was associated with a 4% increase in wages for men and a 6% increase for women10. However, in this review HP estimates differ greatly among studies. Further, there are methodological difficulties in accurately quantifying the relationship between height and wages, including ascertaining whether the relationship is associative or causal, and estimating the contribution of height to wages independent of its many covariates5,11. Different statistical methods commonly are used to examine the relationship between height and wages. Controlling for unobserved variables where possible, including through use of instrumental variables (IV) methods, in some cases substantially increases the magnitude of the association between adult height and wages compared to estimates derived using ordinary least squares (OLS) methods12,13. The relationship between height and wages is attenuated, though usually remaining significant, when controlling for potential confounders such as family characteristics (e.g., parental education and income, number of siblings, etc.), which are precedent determinants of adult height that are also independently associated with wages10,14. Moreover, in the economic literature it is common to adjust for mediating variables, for example, cognitive skills and schooling attainment, which also are likely to reduce the magnitude of association10,14. However, it is important also to note that adjusting for factors that mediate the relationship between height and wages can induce mediator-outcome bias in estimates15. Further, factors like sex and country income may also contribute to differences in the effect size. As a result, it is not clear whether differences in estimates are due to statistical methods or true underlying differences among study populations.
HP estimates are an important input into economic models calculating the potential economic benefits arising from improving child height, and eventually adult height outcomes with public health and nutrition interventions. Within the past several years, such models have been developed to estimate the economic impacts of a package of childhood nutrition interventions16,17. Recently, interest in better understanding the HP has expanded beyond the nutrition field to encompass other interventions, such as a Shigella vaccine that might mitigate infection-related growth faltering18. This attention from the enterics field to better understand and estimate the magnitude of the potential long-term productivity benefits that could result from vaccination prompted the literature review and meta-analysis presented in this paper. Our analysis describes the difference between IV and OLS estimates and examines potential effect modification of the association of adult height with wages by sex and country income category that also may contribute to differences in the magnitudes of the associations. The different estimates produced by our analyses are intended to help clarify how these differences in methodology influence the magnitude of HP estimates, as well as potential underlying differences in the magnitude of the association by sex and country income category.
This review builds on the only published review of which we are aware on linear growth and economic outcomes10. While this prior review was conducted for child stunting outcomes, given the limited longitudinal evidence measuring both child height and adult wages, much of the included literature measured associations between adult height and wages. This prior review included studies published up to July 2015 that assessed the association of childhood stunting or other measures of undernutrition with adult economic outcomes. The literature search was conducted using the PubMed and EconLit databases. A list of keywords used is included in the Supplementary Materials.
The present review included any studies from this prior review that met the following criteria: (a) either used OLS methods to analyze changes in HP estimates when controlling for common confounding variables, or (b) calculated both OLS and IV HP estimates for the same population. We included studies that presented the percentage change in wages associated with an additional unit (cm/inch) of height. Results from 4 additional studies presenting estimates meeting the above criteria, which were identified in the course of the review process, were also included13,19–21. The final studies included in the present review include 2 studies using twins fixed-effects methods (which also present OLS and IV estimates)13,22, 7 studies using IV methods (which also present OLS estimates)20,23–28, and 13 studies using OLS methods1–3,19,21,29–36.
Data abstraction included information on study design, database, sample size, country setting, sex, birth year of participants, age of measurement, statistical model used to assess the association of height and wages, definition of wages (i.e., hourly, monthly, annual), and unit of height measurement (inch/cm). Country income category was assigned using World Bank country income categories from the year of publication.
HP estimates and standard errors were extracted for all relevant coefficients. For OLS studies, these included changes in coefficient estimates when adjusting for common covariates and mediators. We extracted the low-adjusted “bivariate” estimates adjusting for variables such as age, race/ethnicity and region of residence (specific variables adjusted for varied by study and are detailed in the Supplementary Materials). We also extracted high-adjusted “final” estimates, which generally included both confounders and mediators, and included in the meta-analysis any estimates which adjusted for one mediator covariate of interest: either cognitive skills or schooling attainment or both. Fixed-effects estimates, including those from twins studies, were not included in the OLS dataset but were recorded separately. We recorded all IV estimates reported in included studies, along with the type of IV used for height. Where studies presented more than one IV, we selected the estimate that the study reported as its best or final estimate, or with the smallest standard error. To simplify presentation of results, IV estimates were grouped into distinct categories as follows. “Computations” comprised studies using statistical calculations as an IV, including residuals of OLS parameter estimates. “Locality” included characteristics of birthplace such as urban/rural, local prices and number of health institutions present. “Lagged measurements” represented measurements, usually anthropometric, from an earlier point in time, which were used to reduce measurement error in estimates. “Family and ethnicity” included race and ethnic group variables along with parental socioeconomic characteristics. “Combinations” were IVs combining variables from multiple categories.
The objective of the meta-analysis was to produce pooled estimates for studies using different methodologies (IV and OLS) and adjusting for different covariates and mediating variables (low- and high-adjusted estimates from OLS studies), and to examine whether there was evidence of effect modification of the HP by sex and country income category. These represented two potential effect modifiers of interest for which data were available from all studies.
The meta-analysis was conducted in Stata 17 software using the “metan” command. Analysis was performed separately for OLS and IV estimates. We were not able to test the statistical significance of the difference between OLS and IV estimates since traditional meta-analytical methods do not allow multiple observations to be included in one model from the same study population. Random effects models were used due to high heterogeneity in our sample, and our understanding that the HP would differ across studies and contexts37. The DerSimonian and Laird method with random effects was used to calculate the pooled summary effect size. The proportion of total variation in the included studies that was due to heterogeneity was reported using Cochran’s Q P-value and the I2 statistic. An influence analysis was conducted to assess influence of individual studies on overall results38.
We conceptualize the relationship between adult height, a proxy for cumulative nutritional exposures early in life, with wages in Figure 1. Table 1 presents a list of studies included in the analysis, including the HP estimates extracted from each study. Further detail on OLS and IV estimates, including a list of covariates adjusted for in each estimate and categories for IV estimates, can be found in the Supplementary Materials (Tables S1 & S2). Briefly, 9 publications presented HP estimates using the IV methodology and included data from 12 different country analyses. Thirteen publications presented HP estimates using the OLS methodology and used data from 15 different country analyses. Studies conducted using IV methods also presented 12 country analyses using OLS estimates for a total of 24 country analyses using OLS methods. Countries represented in IV studies were predominantly high-income countries (HICs) including the United States and Europe (42%) and lower-middle-income countries (LMICs) including Pakistan and China (33%), with fewer studies conducted in upper-middle-income countries (UMICs; 8%) and low-income countries (LICs; 17%). Similar to IV studies, countries represented in OLS studies were predominantly HICs (58%) and LMICs (25%), and less commonly were UMICs (8%) and LICs (8%). The age at which height and wages were measured ranged from 15 to 64 years old. Measurement of wages ranged from hourly to lifetime; more than half of IV studies (58%) and OLS studies (60%) reported hourly wages. Sample sizes ranged from 427 for an IV study in Tanzania24 to nearly 450,000 for an OLS study using military records in Sweden32.
A descriptive analysis of the HP estimates is presented in the Supplementary Materials.
OLS estimates | IV estimates | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Low-adjusted† | High-adjusted‡ | ||||||||||
Reference | Country (year) | Data | Age height & wages measured | N | Men | Women | Men | Women | Men | Women | Wages measured |
Instrumental variables studies | |||||||||||
Behrman & Rosenzweig 2001 | USA (born 1936–55) | Minnesota Twin Registry follow- up survey | 39–58 | 808 | 0·65%***◊ | -- | 0.32%* | 2.17%* | Hourly | ||
Böckerman & Vainiomälki 2013 | Finland (1990–2004) | Older Finnish Twin Cohort Study | Varied | 1284 | 3.32%*** | 1.41%** | 12.38% (NS) | 11.55%** | Lifetime | ||
Bossavie 2021 | Pakistan (2013) | Labor Skills Survey (LSS) | 15–64 | 1419 | 0·78%***◊ | 0·46%* | -- | 3·56%* | -- | Monthly | |
Elu & Price 2013a | China (2006) | China Health and Nutrition Survey: CHNS | Varied | 1949 | 0.6%** | 0.8%** | 5.1%** | 6.8%** | Monthly | ||
Elu & Price 2013b | Tanzania (2004) | Tanzanian Household Worker Survey | 15–60 | 427 | 1.81%*** | -1.1%*** | 6.5%*** | -4.0%*** | Hourly | ||
Gao & Smyth 2010 | China (2005) | China Urban Labour Survey | 16+ | 8919 | 1.00%*** | 0.87%*** | 4.50%** | 7.32%** | Hourly | ||
Heineck 2005 | East Germany (2003) | German Socio- Economic Panel: GSOEP | 21–50 | 24000 | 0.56%*** | 0.17%** | 0·58% (NS) | 0·34% (NS) | Gross monthly | ||
Heineck 2005 | West Germany (2003) | GSOEP | 21–50 | 24000 | 0.29%*** | 0·07% (NS) | 0.52%* | 0·53% (NS) | Gross monthly | ||
Schultz 2002 | Brazil (1989) | Health and Nutrition Survey | 25–54 | 11855 | 1.40%*** | 1.66%*** | 7.01%*** | 8·62%*** | Hourly | ||
Schultz 2002 | USA (1989–93) | NLSY 1979 | 20–28 | 9257 | 0.45%*** | 0.31%** | 3.62%*** | 6.24%*** | Hourly | ||
Schultz 2003 | Ivory Coast (1985–89) | Living Standards Measurement Surveys: LSMS | Varied | 2872 | 0.86%** | 0·42% (NS) | -1·05% (NS) | -4·18%* | Hourly | ||
Schultz 2003 | Ghana (1985–90) | LSMS | Varied | 6814 | 1.48%*** | 1.29%*** | 5.56%*** | 7.62%*** | Hourly | ||
OLS studies | |||||||||||
Bargain & Zeidan 2017 | Indonesia (2007) | Indonesia Family Life Survey (IFLS) | Mean=39 | 7878 | 2·54%*** | 1·40%*** | -- | Annual | |||
Case & Paxson 2008 | England (1991) | NCDS | 33 | 9855 | 0·91%*** | 0·75%*** | 0·47%*** | 0·28% (NS) | Hourly | ||
Case & Paxson 2008 | England (2000) | British Cohort Study: BCS | 30 | 4380 | 0·39%*** | 0·59%*** | 0% (NS) | 0·12% (NS) | Hourly | ||
Case & Paxson 2010 | USA (1988–97) | Panel Study of Income Dynamics: PSID | 25–55 | 31999 | 0·57%*** | 0·26%*** | 0·26%** | 0·12% (NS) | Hourly | ||
Case et al 2009 | England (1997–2005) | British Household Panel Survey: BHPS | 21–60 | 42666 | 0·71%*** | 0·59%*** | 0·16%** | 0·12%* | Hourly | ||
Heineck 2008 | England (2004) | BHPS | 21–50 | 4650 | 0·25%* | 0·55%*** | -0·05% (NS) | 0·20%* | Gross hourly | ||
Lindqvist 2012 | Sweden (2006) | Longitudinal INdividual DAta for Sweden: LINDA | Varied | 13446 | 0·56%*** | 0·33%*** | -- | Annual | |||
Lundborg et al. 2014 | Sweden (2003) | Military records | Height: 18 Wages: 28–38 | 448702 | 0·62%*** | 0·52%*** Ώ | -- | Annual | |||
Persico et al. 2004 | USA (1996) | NLSY 1979 | Height: 20–27 Wages: 31–38 | 1577 | 0·98%*** | 0·71%** Ώ | -- | Annual | |||
Persico et al. 2004 | England (1991) | NCDS | 33 | 1772 | 1·06%*** | 0·87%*** Ώ | -- | Period varied | |||
Rietveld et al. 2015 | Germany (2002–12) | GSOEP | 18–65 | 92248 | 0·51%*** | 0·26%*** | Hourly | ||||
Sargent & Blanchflower 1994 | England (1981) | NCDS | Height: 16 Wages: 23 | 12537 | 2·3%** | 0·90% (NS) | Hourly | ||||
Schick & Steckel 2015 | England (2000) | NCDS | 33 | 2577 | 0·87%***◊ | 0·75%***◊ | 0·20% (NS) | 0·00% (NS) | Hourly | ||
Sohn 2015 | Indonesia (2007) | IFLS | 20–65 | 13243 | 3·58%* | 4·44%* | 0·75%** | 1·30%** | Annual | ||
Vogl 2014 | Mexico (2002, 2005) | Mexican Family Life survey: MxFLS | 25–65 | 3860 | 2·30%*** | 1·4%*** | -- | Hourly |
Significance of results: 0·05%: *; 0·01%: **; 0·001%: ***
† OLS estimate adjusted with minimal controls, those included in the meta-analysis did not adjust for mediator covariates. Full list of controls for each study is presented in Supplementary Materials.
‡ OLS estimate adjusted for the most controls, including at least one mediator covariate. Full list of controls for each study is presented in Supplementary Materials.
◊ Low-adjusted estimate includes potential confounding variables and was not included in meta-analysis.
Ώ High-adjusted estimate does not include mediator covariate and was not included in meta-analysis
Results from the meta-analysis of the association between sex and wages are presented separately for IV studies (Figure 2) and for OLS studies that are low-adjusted (Figure 3) and high-adjusted including at least one mediator covariate (Figure 4). Results of the meta-analysis of the association between country income category and wages are presented separately for IV studies (Figure 5) and OLS studies that are low-adjusted (Figure 6) and high-adjusted including at least one mediator covariate (Figure 7).
Overall, the pooled estimates for IV studies were the greatest in magnitude and indicated that each centimeter increase in height was associated with 3.58% greater wages (95% CI: 1.62-5.54%; I2=97.5%, p<0.001)). For OLS studies, the pooled estimates of low-adjusted OLS estimates indicated that each centimeter increase in height was associated with 1.06% greater wages (95% CI: 0.85-1.28%, I2=95.5%, p<0.001), while high-adjusted OLS estimates which included adjustment for mediators were the smallest in magnitude and indicated that each centimeter increase in height was associated with 0.57% greater wages (95% CI: 0.41-0.73%, I2=95.8%, p<0.001). Of note, there was high heterogeneity indicated by I2 statistics in each analysis.
Results from the influence analysis are presented in the Supplementary Materials and indicated that several studies appeared to have meaningful influence on the overall estimates (Tables S7-S10). For the pooled estimates of the effect of sex in IV studies, after exclusion of a study from Germany26 the pooled estimate for males was 4.42% (95% CI: 2.93-5.92%), while after exclusion of a study from Brazil27 the pooled estimate for females was 2.58% (95% CI: -0.09-5.25%). For the pooled estimates of the effect of sex in low-adjusted OLS estimates, after exclusion of a study from Indonesia35, the pooled estimate for males was 0.86% (95% CI: 0.67-1.06%), and for females was 0.52% (95% CI: 0.36-0.68%). For the pooled estimates of the effect of sex in high-adjusted OLS estimates, after exclusion of a study from Tanzania24, the pooled estimate for males was 0.60% (95% CI: 0.46-0.74%), while after exclusion of a study from Brazil27, the pooled estimate for females was 0.29% (95% CI: 0.05-0.53%).
For the pooled estimates of the effect of country income category in IV studies, after exclusion of a study from Germany26, the pooled estimate for HICs was 2.78% (95% CI: 0.79-4.78%), while after exclusion of a study from the Ivory Coast28, the pooled estimate for LMICs was 3.94% (95% CI: 1.43-6.44%). Finally after exclusion of a study from Tanzania24, the pooled estimate for LICs was 6.49% (95% CI: 5.97-7.02%). For the pooled estimates of the effect of country income category in low-adjusted OLS estimates, after exclusion of a study from Indonesia35, the pooled estimate for LMICs was 3.05% (95% CI: 2.03-4.07%). For the pooled estimates of the effect of country income category in high-adjusted OLS estimates, after exclusion of a study from Tanzania24, the pooled estimate for LICs was 1.67% (95% CI: 1.37-1.97%).
In the meta-analysis of studies presenting IV estimates there was not an indication of a statistically significant difference in the magnitude of the association of adult height with wages by sex (p=0.794). However, considerable heterogeneity remained after stratifying by sex (male I2 = 96.3%, p<0.001; female I2 = 96.4%, p<0.001)39.
In contrast, in the meta-analysis of low-adjusted OLS estimates, there was no indication of a statistically significant difference in the magnitude of the association of adult height with wages by sex (p=0.922) and considerable heterogeneity remained after stratifying by sex (male: I2 = 96.0%, p<0.001; female: I2 = 95.1%, p<0.001).
In the meta-analysis of studies presenting high-adjusted OLS estimates including adjustment for mediators, there was an indication of a statistically significant difference in the magnitude of the association of adult height with wages by sex (p=0.041) and considerable heterogeneity remained when stratifying by sex (male: I2 = 95.8%, p<0.001; female: I2 = 94.6%, p<0.001).
In the meta-analysis of studies presenting IV estimates, there was an indication of a statistically significant difference in the magnitude of the association of adult height with wages by country income category (p<0.001). This difference was driven by estimates from UMIC studies that were larger than estimates from other country income strata. Among UMICs each centimeter increase in height was associated with 7.57% greater wages (95% CI: 6.07-9.07%). However, there were a small number of observations in this income strata subgroup (n=2 IV observations from 1 publication). In the meta-analysis of IV estimates, among HICs, each centimeter increase in height was associated with 2.24% greater wages (95% CI: 0.89-3.60% while for studies in LMICs each centimeter in height was associated with 2.90% greater wages (95% CI: -0.14-5.94%). Finally, among LICs each centimeter in height was associated with 3.86% greater wages (95% CI: -3.22-10.94%). The level of heterogeneity remained high when stratifying by country income category in HIC (I2 = 82.8%, p<0.001) and LIC estimates (I2 = 99.5%, p<0.001), with substantial heterogeneity in LMIC estimates (I2 = 69.5%p=0.003), and moderate heterogeneity in UMIC estimates (I2 = 44.3%, p=0.180).
In the meta-analysis of studies presenting low-adjusted OLS estimates, there was an indication of a statistically significant difference in the magnitude of the association of adult height with wages by country income category (p<0.001). This subgroup analysis only included pooled estimates for HIC and LMIC as no low-adjusted OLS estimates were available from LIC studies and only one estimate was available from a UMIC study. In the meta-analysis of low-adjusted OLS estimates, among HICs, each centimeter increase in height was associated with 0.59% greater wages (95% CI: 0.50-0.67%). In LMICs, each centimeter increase in height was associated with 3.48% greater wages (95% CI: 2.45-4.50%). The level of heterogeneity varied when stratifying by country income category with substantial heterogeneity in HIC estimates (I2 = 59.0%, p=0.003), and considerable heterogeneity in LMIC estimates (I2 = 91.2%, p<0.001)).
In the meta-analysis of studies presenting high-adjusted OLS estimates that included adjustment for mediators, there was an indication of a statistically significant difference in the magnitude of the association of adult height with wages by country income category (p<0.001). This difference was due to substantially higher average estimates for UMICs. However, there were a small number of observations in this income strata subgroup (n=3 OLS observations from 2 publications). In the meta-analysis of high-adjusted OLS estimates, among HICs, each centimeter increase in height was associated with 0.26% greater wages (95% CI: 0.19-0.34%). Among UMICs, each centimeter increase in height was associated with 1.48% greater wages (95% CI: 1.27-1.69%). In LMICs, each centimeter increase in height was associated with 0.88% greater wages (95% CI: 0.68-1.09%). Finally, among LICs each centimeter in height also was associated with 0.86% greater wages (95% CI: -1.04-2.76%). The level of heterogeneity varied when stratifying by country income category with low heterogeneity in UMIC estimates (I2 = 0.0%, p=0.547), moderate heterogeneity in LMIC estimates (I2 = 37.2%, p=0.111) and considerable heterogeneity in HIC (I2 = 76.8%, p<0.001) and LIC estimates (I2 = 99.6%, p<0.001)).
We conducted a meta-analysis of economic literature presenting estimates of the height premium (HP), or the association between adult height and labor-market wages, including 9 studies using IV methods and 13 studies using OLS methods with analyses conducted in primarily high-income (HIC) and lower-middle income countries (LMIC). We analyzed estimates separately based on methodology (IV and OLS) and to what degree OLS estimates adjusted for mediator variables. Our meta-analysis of IV studies found that overall, each centimeter increase in adult height was associated with 3.58% greater wages. Our meta-analyses of OLS studies found each centimeter of adult height to be associated with 1.06% greater wages in estimates which were “low-adjusted” for confounding variables (age, race/ethnicity and province/region of residence) and 0.57% greater wages in estimates which were “high-adjusted” for at least one mediator variable. As a result, this suggests that statistical methods contribute to differences in HP estimates across studies. In addition, we also found within analyses using similar methods there were differences in the magnitude of the HP association by sex and country income group which suggests there also may be true underlying differences in the magnitude of the association by study population and context. Therefore, our findings suggest that both statistical methods and underlying differences between study populations and context contribute to heterogeneity in HP estimates.
In analyzing OLS and IV results separately, we found appreciable differences in effect sizes between the two methods. Further, the pooled estimate from OLS analyses which were low-adjusted for confounding variables was nearly twice as large, on average, as the pooled estimate from high-adjusted OLS analyses which adjusted for at least one mediator variable. As a result, the pooled estimate from IV studies was over 3 times larger than the pooled low-adjusted OLS estimate and over 6 times larger than the pooled high-adjusted estimate from OLS studies. This wide range of HP estimates challenges their interpretation and has implications for identifying a narrower range of plausible estimates for use in economic models estimating the returns to investments that could improve child, and eventually adult height.
OLS parameter estimates are biased if there are confounders that should be in the model but are not and that are associated with both nutritional exposures and adult wages27. It is very possible that in OLS estimates there is not complete control for confounding and there are other sociodemographic characteristics and other factors that should be in the model but that are not captured through adjustment for parental education and income, for example. Further, there is the possibility of residual confounding if the confounders are mismeasured or are included as covariates that do not fully capture the relationship. It is likely the not-included and residual confounding would lead to overestimates of the association given that poor sociodemographic and other poverty-related factors, which may not be not fully adjusted for, are more common in individuals experiencing growth deficits. OLS studies in the economic literature also often adjust for mediating variables that contribute to wages, such as cognitive skills, schooling attainment and several others. Generally, adjustment for mediators will attenuate estimates, but it can also produce mediator-outcome confounding which can bias estimates in any direction15. In the studies included in the meta-analysis, most studies adjusted for mediators like cognition and schooling that are likely the major pathways for the association of adult height with wages, and which likely outweigh any mediator-outcome confounding. Therefore, the magnitude of our pooled estimate is likely attenuated as compared to the true total effect.
The IV method corrects for unobserved confounding and attenuation bias by assuming that height is endogenous and measured with error and “instrumenting” it with other variables that are linked to one of the sources of variation in height, not related to unmeasured confounders, and only linked to the wage outcome through the effects on height (e.g., regional food prices)40. This isolates the effect on wages of the different components of height28,41. Identifying valid IVs can be challenging, however, and some of the assumptions made cannot be formally verified but rely on analysts’ understanding, along with intuition42. Further, it is important to note that IV estimates provide “local average treatment effects” that represent the effect for a subset of the population for which the instrument has effects43, thereby putting into question their use to represent general population-level effects. There is controversy around use of IVs, with some critics considering the larger associations sometimes found with IVs relative to OLS methods to be “implausible”19,35. Some analysts claim that under most circumstances both IV and OLS methods produce estimates with similar errors44. One seminal study presented a recommended list of valid IVs, representing variables which are correlated with height but not with adult wages except through height27. These included (1) variables representing a “local price of health” such as environmental or climactic conditions, and a community’s supply of health-related services and infrastructure, (2) “endowments and lifetime income constraints” including family labor market decisions and human capital investments in their children, (3) variables such as the local supply of education services which are correlated with children’s schooling but not their abilities, and (4) race and ethnicity27. Compared with this list of recommended IVs, more than one-half of the IVs included in the present review were computations, or statistical calculations used as IVs, and combinations of different variables. This indicates that there may not be common agreement in the literature on which IVs to use, or potentially that choice of valid IVs differs by context, which could be a potential source of bias in IV estimates.
Our meta-analysis showed that for high-adjusted OLS estimates, but not for low-adjusted OLS estimates or IV estimates, there was some evidence that the strength of the association between height and wages differed by sex, though the magnitude of the difference was relatively small (0.34% greater for males). The significant difference in estimates adjusted for mediators of cognitive skills and schooling suggests the potential of a differential sex effect of these mediating variables on wages. This could be due to differential discrimination for shorter women, or differential schooling attainment by sex as has been suggested in previous studies22,33,45,46.
Further, our analysis produced evidence that the strength of the association between height and wages differed by country income category for both OLS and IV estimates, though our analysis included limited evidence from UMICs and LICs. This could be due to differential quality of schooling and potential future job market opportunities among different country income strata which could influence wages and potentially could shape parents’ resource allocation decisions, particularly regarding schooling. Differences in HP among country income strata have been noted in previous studies47 which cautioned that the result could be due to heterogeneity in measurement of wages and different methodologies among studies from different country income categories10.
This work has several limitations. This review was based on a prior review published in 2017, which may not have been conducted using fully systematic methods, including assessment of study quality and a sufficiently rigorous literature search to identify a comprehensive list of relevant studies48. The present review would have missed any studies not included in the prior review and, as it was not systematically updated to capture any studies published in the interim, is not an exhaustive review of the literature. Future research could apply systematic review methods to the HP literature, to assess whether results change appreciably. However, when comparing our results with those of other reviews, we find a general trend of HP estimates and do not conclude that identifying more studies would be likely to alter substantially our general findings. While we were able to compare our pooled estimates of OLS and IV studies separately and discuss these general differences, future research could test these differences formally. Finally, significant heterogeneity in the methodology of included studies limited our ability to extrapolate from the meta-analyses. Finally, most of the studies that used OLS were from HICs; more studies should be conducted in low- and middle-income countries to improve the evidence base in these settings.
Despite these limitations, this review has added to the literature by applying meta-analytical methods to the HP literature for the first time, to our knowledge, to assess statistically whether the magnitude of estimates of the HP differ by sex and country income category. Our findings suggest that differences in HP estimates are attributable to both differences in statistical methods and potential differences by sex and country income. Separating HP estimates by IV and OLS methodology is advisable as the method of analysis appears to be central to the effect sizes. It is also important for researchers to understand the assumptions and potential for bias based on the selection of covariates, and it is important to recognize that adjustment for mediators will likely attenuate associations. Better understanding of the effects of height on wages can contribute to more refined economic models estimating improvements in future economic productivity due to improving growth from conception through adulthood. Measurement of these benefits also has implications for interventions addressing any of the many interconnected causes of linear growth faltering. Additional research is needed to define the association of adult height with wages taking into account potential underlying differences by context and to better understand differences in statistical methodologies to address this complex relationship.
All data underlying the results are available as part of the article and no additional source data are required.
Figshare: Height premium meta-analysis Supplementary Materials. https://doi.org/10.6084/m9.figshare.2361864649
This project contains the following extended data:
Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).
We would like to thank Dr. Sue Horton for her guidance at the early stages of this analysis. We extend sincere thanks to Isaac Miller for his work in developing and formatting forest plots.
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Is the work clearly and accurately presented and does it cite the current literature?
Partly
Is the study design appropriate and is the work technically sound?
Yes
Are sufficient details of methods and analysis provided to allow replication by others?
Partly
If applicable, is the statistical analysis and its interpretation appropriate?
Yes
Are all the source data underlying the results available to ensure full reproducibility?
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Are the conclusions drawn adequately supported by the results?
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References
1. Vogl T: Height, skills, and labor market outcomes in Mexico. Journal of Development Economics. 2014; 107: 84-96 Publisher Full TextCompeting Interests: No competing interests were disclosed.
Reviewer Expertise: health demography, life-course approaches, living standards
Is the work clearly and accurately presented and does it cite the current literature?
Partly
Is the study design appropriate and is the work technically sound?
Partly
Are sufficient details of methods and analysis provided to allow replication by others?
Yes
If applicable, is the statistical analysis and its interpretation appropriate?
Yes
Are all the source data underlying the results available to ensure full reproducibility?
Yes
Are the conclusions drawn adequately supported by the results?
Yes
References
1. Thompson K, Portrait F, Schoonmade L: The height premium: A systematic review and meta-analysis.Econ Hum Biol. 2023; 50: 101273 PubMed Abstract | Publisher Full TextCompeting Interests: No competing interests were disclosed.
Reviewer Expertise: Economics
Is the work clearly and accurately presented and does it cite the current literature?
Yes
Is the study design appropriate and is the work technically sound?
Partly
Are sufficient details of methods and analysis provided to allow replication by others?
Partly
If applicable, is the statistical analysis and its interpretation appropriate?
Yes
Are all the source data underlying the results available to ensure full reproducibility?
Yes
Are the conclusions drawn adequately supported by the results?
Yes
Competing Interests: I was a co-author on the Cost of Stunting to the Private Sector paper (which estimated individual economic losses as well as firm losses due to a range of factors, incl. height) that was published post-2017 and was alluded to in my review. I am currently employed at the Children’s Investment Fund Foundation, alongside my appointment at JHU. I do not have any involvement in economic analysis (or funding it) on HP at CIFF, but given CIFF is a donor would like to declare for transparency.
Reviewer Expertise: Systematic Review Methodology, Nutrition, Child Health, Newborn Health, Maternal Health, Epidemiology, Research Priority Setting, Mixed Methods, Evaluation, Adaptive Design Evaluation
Alongside their report, reviewers assign a status to the article:
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