The INCAP longitudinal study (1969-77)

Objectives and design. The design eventually implemented in the INCAP longitudinal study called for comparison of outcomes in pregnant and lactating women and in their children between two pairs of villages exposed to different supplements. Read and Habicht (1992) state that the major motivation for the INCAP longitudinal study was to assess the impact of intrauterine and preschool malnutrition on behavior. Thus, food supplements were provided and their consumption measured in pregnant women and in children younger than 7 y of age.

Nutritional supplementation was to produce an unambiguous contrast between well and poorly nourished children. Because protein deficiency was perceived to be the major cause of malnutrition at the time the study was being planned (Scrimshaw and Behar 1965), major emphasis was placed on improving protein malnutrition while assuring enough extra energy to allow for protein utilization. The feeding intervention took advantage of INCAP's extensive experience with Incaparina (Bressani and Elias 1968), a nutritious gruel with a high-protein and moderateenergy content that was widely accepted in Guatemala. Thus, the pregnant mothers' and childrens' diets were improved with an Incaparina-based drink, referred to as "Atole", the Guatemalan name for a hot, maize gruel. This drink had to be prepared at the time of ingestion and therefore required a central kitchen and feeding hall.

The centrally located feeding stations precluded random allocation of treatment to individuals within a village; instead, allocation to treatment was by village within pairs chosen to be as similar as possible. One pair was large (~900 people per village) and one was small (~500 people per village).

The comparison beverage to this gruel was a sweet, cool, colored and fruit-flavored drink called "Fresco". Drinks of this type were much appreciated in the area. The Fresco was intended originally to be devoid of any nutritional value, in effect to be a placebo. It was envisaged as a control for the social stimulus and other factors associated with supplementation. The use of cyclamates for sweetening was considered but concern about carcinogenicity led to sugar being used instead, which of course introduced energy. Finally, other nutrients were introduced as discussed below in an attempt to narrow the contrast between the Atole and Fresco groups to differences in energy and above all in protein. Consequently, the Fresco should not be viewed as a placebo control to the Atole because it contained some energy and important concentrations of micronutrients. Instead, both drinks are referred to as "supplements".

Originally, three pairs of supplementation villages were specified, but budgetary constraints reduced the number of pairs to two. A less accessible pair of "large" villages was dropped early in the study with dire consequences for statistical power. As implemented, the effects of improved protein nutrition were to be ascertained through comparisons of results before and after the intervention in the two Atole and two Fresco villages. The before-after comparison was, however, only possible for selected variables collected with adequate sample sizes in 1968, before the intervention began, or for those variables collected in the first months of the study that could not be immediately affected by supplementation (e.g., height of 7y-old children). Issues of statistical power and analytic strategies in the study are discussed extensively by Habicht, Martorell and Rivera (1995).

The effect due to the study activities per se on behavior was to have been estimated by contrasting outcomes before and after the study in the villages not receiving protein (i.e., Fresco villages) to those in villages not visited in the interim, termed "Supercontrol" villages in project documents. However, budgetary constraints curtailed baseline data collection in these "Supercontrol" villages, nor were data collected in these communities in 1977, at the end of the INCAP longitudinal study.

Although the allocation of treatment across villages was random, ingestion of the supplements was voluntary and therefore subject to self-selection. The implication of this combination of random error and selfselection bias for data analysis and interpretation is discussed by Habicht, Martorell and Rivera (1995).

Finally, it is important to consider that conducting the study involved intensive contact between data collectors and villagers. The data-collection activities were designed and implemented to affect all villages equally and therefore cannot be a source of bias in the Fresco versus Atole contrasts. However, the study setting does affect the validity of extrapolations to other populations if its activities impacted on outcomes synergistically with the supplements. These same concerns apply to the medical care that was provided to the study villages; it too may have potentiated or diminished the impact of the supplements.

Village selection and description. Several needs were considered in selecting villages: population size, relatively compact settlements; to allow easy access to the centrally located feeding station and stability and homogeneity among villages. A further limitation was imposed by the psychometric testing. To find a large enough sample of mutually isolated villages speaking the same language, the study had to be located in the Spanish-speaking (i.e., Ladino) region of Guatemala instead of in the more picturesque Maya-speaking area where most previous INCAP research had been done. The selection and matching criteria that were used are presented in Table 1.

TABLE 1 Criteria for selecting and matching villages in the INCAP Longitudinal Study¹

Area	Criteria
Ethnicity	100% Spanish-speaking, Ladino culture (i.e., not Indian)
Population	500-1000 inhabitants
Birth rate	35-45/1000 live births annually
Death rate	14-18/1000 population annually
Age distribution	Birth-6 ys: 24-30%
	Birth-15 ys: 35-50%
	16-45 y: 40-45%
	³ 55 ys: 5-10%
Family composition	Average of five family members per nuclear family
Population mobility	80% or more born in area; 2% annual migration, with little likelihood of change
Social isolation	50 - 150 km from Guatemala City; any village included in the study should be ³ 10 km from other selected villages and under the jurisdiction of a different municipality (i.e., county)
Transportation	Accessible by four-wheel drive vehicles
Compact nuclear settlement	80% of homes within 1-km radius from the community research center
Housing and community services	60% similarity across villages
Annual income	$200 ± $50 per family unit
Education level	30% literacy among population ³8 y
Basic foods	Corn and beans
Health and nutrition	High levels of malnutrition and of gastrointestinal and respiratory disorders. Anthropometric, dietary and morbidity information of 10 villages which satisfied best the above criteria were considered in selecting the most similar pairs of large and small villages.

¹ Adapted from Canosa et al. 1972.

Ultimately 10 villages were found to fulfill best these selection criteria from among 300 Ladino villages identified from maps as being within the selection radius and from the Guatemalan Census as having population sizes of 500-1000 inhabitants (Canvass et al. 1972). This was a time-consuming process entailing data collection in as many as 45 villages. Most of these data are lost except for some of the dietary, anthropometric, census and socioeconomic data collected in the four villages finally selected for the study. Some useful baseline information about the four study villages is given by Mejía-Pivaral (1972).

Analyses of baseline data indicated that three pairs of villages were most similar to each other: two pairs of villages within an hour's jeep ride from each other and a third pair of villages much further away. As noted earlier, the study was never fully implemented in the third pair of villages, Tapalapa and Santa Gertrudis. The final two pairs of villages selected were San Juan de las Flores and Espiritu Santo with ~500 inhabitants each and San Miguel de Conacaste and Santo Domingo los Ocotes with ~900 inhabitants each. All were far enough apart from each other to make intervillage contact unlikely.

The four villages selected are located in the Department of El Progreso, a dry, mountainous area northeast of Guatemala City. The large Fresco village (Santo Domingo) is closest to Guatemala City, at 36 km, whereas the small Fresco village (Espíritu Canto) is furthest, at 102 km. The elevation of the large Fresco village is 1250 m above sea level, whereas both Atole villages are at 860 meters, and the small Fresco village is at 275 meters. The average temperature range for the small Fresco village is 24-38°C, and for the other three villages it is ~14-32°C with the rainy season occurring from June to October. Two of the major crops in each village were corn and beans, with tomatoes also being a major crop in the large Atole (Conacaste) and small Fresco villages, sorghum in the large Fresco village, and maniac, locally known as "yuca," in the small Atole village (San Juan).

In 1967, <10% of the families in the four villages had a source of water in their homes. Almost everyone obtained water from open, unprotected hand-dug wells, and in the small Fresco village from a nearby river. Few households had a latrine, and no one had a sewage or drainage system.

In three of the four villages, the typical house had one to two rooms with adobe walls, dirt floors and a tile or metal roof. However, poorer families lived in houses with reed walls and thatched roofs. In the small Fresco village, where the climate is warmest, most houses, even those of better-off families, had thatched roofs, walls made of reeds and mud, and dirt floors. Families usually prepared food in either a separate room or in a separate area located just outside the house. Most people owned their homes, as well as at least some of the land around their homes. About onethird of the families had radios; only a few (<5%) owned a television, record player, refrigerator or bicycle. No homes were equipped with electricity.

The primary income for most villagers was from agricultural production. Almost all were tenant farmers or small-land owners. No one in any of the villages reported being a large landholder, and very few reported being merchants. Wage labor was reported as a principal occupation by 21% of the men in the small Fresco village and by 15% of the men in the small Atole village. Wage labor was not a significant source of income in the large villages. Very few women reported having occupations outside the household except in the small Fresco village, where they had the opportunity to make money independently through basket weaving.

Literacy was self-reported, usually by the mother of the family, for all family members. The percent of mothers at least partially literate in each village ranged from 25 to 40%. The large Fresco village had the highest literacy rate for mothers (40%). Literacy levels of the fathers ranged from 38 to 60% with those in the small Fresco village having the highest literacy rate. Additional data about the social, economic and demographic development of these villages are given by Bergeron (1992) and Engle et al (1992a).

The interventions: supplementation and medical care. Supplementation. The intervention design calls for comparisons of villages in which pregnant and lactating mothers and their children up to 7 y of age received verified and recorded amounts of either Atole or Fresco. Table 2 presents the ingredients and the energy and nutrient concentration of the supplements per one-cup serving (i.e 180 mL) as given elsewhere (División de Desarrollo Humano 1971; Martorell et al. 1982). The Atole contained a high-quality protein mixture whereas the Fresco contained none. The energy concentration of Atole for children older than 4 mo was 2.8 times greater than for Fresco.

TABLE 2 Formula and nutrient content of beverages per cup serving (180 mL)¹

	Atole		Fresco
	For subjects >4 mo in age	For older subjects	From 69-71	From 71-77¹
Ingredients (g/180 mL)
Incaparina (g)	-	-13.5	-	-
Dry skim milk (g)	28.8	21.6	-	-
Sugar (g)	3.6	9.0	13.3	13.3
Flavoring (g)	-	-	2.1	2.1
Nutrients (per 180 mL)
Energy (kJ)	498	682	245	247
Energy (Cal)	119	163	59	59
Protein (g)	10.3	11.5	-	-
Carbohydrates (g)	15.3	27.8	13.3	13.3
Fats (g)	0.2	0.8	-	-
Calcium (g)	0.4	0.4	-	-
Phosphorus (g)	0.3	0.3	-	-
Iron (g)	0.2	1.2, 5.0²	-	5.0
Fluoride (mg)	-	0.0, 0.2²	-	0.2
Thiamin (mg	0.1	0.4, 1.1²	-	1.1
Riboflavin (mg)	0.5	0.5, 1.5²	-	1.5
Niacin (mg)	0.3	1.3, 18.5²	-	18.5
Ascorbic acid (mg)	-	0.0, 4.0²	-	4.0
Vitamin A (mg)	0.4	0.5	-	0.5

¹ Higher values as of October 1, 1971.
² Values differ slightly for some ingredients and nutrients in project documents. Those given here are from the Manual de Operaciones issued by the División de Desarrollo Humano (1971).

There were two formulations of Atole depending on age: one for children <4 mo of age made up of powdered skim milk and sugar (28,8 and 3.6 g, respectively, per 180 mL) and one for older children and mothers containing Incaparina, skim milk and sugar (13,5 ± 21.6 and 9.0 g, respectively, per 180 mL). Very little of the milk supplement was consumed by children <4 mo of age. The Atole for older children was pale gray-green, and tasted smooth but slightly gritty and sweet; it was served hot. The energy, protein and micronutrient contents of the Atole are shown in Table 2.

In October of 1971, the riboflavin content of the Atole for children >4 mon was raised from 0.5 mg to 1.5 mg per serving after noting that the biochemical indices of riboflavin were not satisfactory in 2-y-old children consuming Atole (Habicht et al. 1973). Iron and a small amount of ascorbic acid to facilitate iron absorption also were added because anemia was common in pregnant mothers; however, anemia was not found in unsupplemented 2-y-old children (Habicht et al.1973). The thiamin and niacin contents increased because they were present in the iron-vitamin mix. On the basis of calculations from knowledge about water fluoridation (Infante 1975), fluoride was also added at this time because the drinking water had a low fluoride content at the end of the dry season 0.166-0.384 ppm compared with the recommended 1 ppm) when the concentrations should be highest and because of the high incidence of dental caries in the communities (Infante and Gillespie 1976; Infante and Gillespie 1977).

The comparison beverage, Fresco, was a low-calorie supplement containing 247 kJ (59 kcal) and no protein per serving. It was a cool, clear-colored, fruit-flavored drink similar to KoolAidä (sold in the USA. The ingredients and nutrient content of the Fresco are given in Table 2. Previous to 1971, it contained only flavoring, color and sugar. In October 1, 1971 other nutrients were added to make it more similar to the Atole. Many of these nutrients had been found to be marginal after review of biochemical indicators in blood and urine in children who drank the Fresco regularly (Habicht et al. 1973).

In all villages, the supplements were distributed and consumed in a centrally located, feeding hall for 2-3 h during midmorning and midafternoon, including weekends. These times were chosen because they were easiest for mothers and children to attend and because they did not interfere with usual meal times.

Medical care. Curative medical care was available on week days and free of charge throughout the duration of the study at a clinic adjacent to the beverage feeding halls. These services were available for all residents and were not tied to participation in any aspect of the study. The medical care program was justified not only on ethical grounds but on design considerations as well. For example, immunizations would prevent an epidemic from striking one village and not another as had happened in a previous INCAP nutrition field trial, with dire consequences for data interpretation.

The new system of curative care was implemented in the fall of 1969 (Working Group 1973). Effective but affordable medical care was provided through auxiliary nurses instead of physicians and by streamlining the purchasing and use of medicines. It featured continuous supervision of adequacy of the quality of history taking, diagnosis and treatment (Habicht 1979). Cases that could not be diagnosed by the auxiliary nurses were referred to the supervisory physician (<1% of cases). Furthermore, arrangements were made with Hospital Roosevelt, a teaching hospital in Guatemala City, to honor referrals (0.4% of cases) and keep INCAP informed of patients' progress and discharge. By early 1971, the quality of care had stabilized and >99% of cases were managed correctly (Working Group 1973).

The local traditional midwives were funded to attend midwifery courses given by the Guatemalan public health authorities. Their care complemented that given on demand by the nurses.

All children were examined 15 d after birth by a well trained pediatrician for diagnosis and treatment of any neonatal ills. The pediatrician also examined the children at 3 mo and at 1, 3 and 7 y to detect any remediable pathology that had escaped the clinic's attention. Pregnant mothers were immunized against tetanus and children against tuberculosis, diphtheria, whooping cough, tetanus, measles and poliomyelitis (Habicht et al. 1979). Deworming medicines were offered twice a year, but the medical program did not give health or nutrition education, except to encourage attendance to the supplementation feeding stations and to participate in immunization campaigns. The curative and preventive health care services were the same in all the villages, and any preventive campaigns such as deworming or immunization were done simultaneously in all the villages.

Compared with rates for the period previous to 1969, infant mortality had declined by 1970-72 from 139 to 55 deaths per 1000 births and preschool mortality had decreased from 28 to 6 deaths per 1000 children at risk, at a total cost for primary health care of<$5 per villager per year. National death rates in Guatemala remained constant during this comparison period. Data collected in 1988-89 confirmed these declines in mortality rates (Rose et al. 1992).

Other influences of the study team. The intensity of data collection and the supplementation and medical interventions required the continuous presence of four to eight well-educated persons in each village. Although they did not live in the villages, at least one of them visited each family twice a month. The influence of these contacts could be variable depending upon the personalities of the personnel and therefore could have affected the outcomes of the study differentially across villages. Therefore all personnel were rotated through all the villages for equal durations of time.

Sample persons, data collection and data availability. All women who were pregnant or lactating and all children from birth to 7 y of age were included in the original design of the INCAP longitudinal study if they lived in the study villages from January 1,1969 to February 28, 1977. Absence from the village was the most common cause for missing data. Refusal to participate in the study was rare; <2% of all families declined participation. Anthropometric data are available for 517 different women for one or more of their pregnancies and corresponding lactation periods. The distribution by birth date cohort of the children with one anthropometric examination or more (n = 1992) is presented in Table 3 by village type. The cohorts identify children with different exposure to supplementation during the critical periods of gestation and the first 3 y of life.

TABLE 3 Children with anthropometry¹ by birth cohort in Atole and Fresco villages

Cohort number	Birth cohorts	Exposure period	Atole	Fresco	Total
I	³1 March 1974	Gestation, partial birth to 3 y	260	280	540
II	1 March 1969-28 February 1974	Partial during gestation,2, all birth to 3 y	374	395	769
III	1 January 1966-28 February 1969	Partial birth to 3 y	185	194	379
IV	³1 January 1966	No exposure during gestation or birth to 3 y	151	153	304
Total			970	1022	1992

¹ With data for birthweight or for any of the anthropometric postnatal examinations.
² Some cases in the early part of the study may not have had full exposure to supplement during pregnancy.

Details of data collection are shown in Table 4. Most data collection began January 1, 1969 in the large villages and somewhat later (range March to May) in the small villages. All data collection ceased in September 1977 but cessation occurred as early as March 1977 for some types of information. Data-collection methods are described in detail in a manual of standard operating procedures in which the forms used are also presented (Division de Desarrollo Humano 1971). Table 4 also lists data collected in cross-sectional surveys conducted in collaboration with the Rand Corporation in 1974-76; additional details are given elsewhere (Corona 1980). Short descriptions of the type of data collected in key areas are presented below.

Census and socioeconomic data. A census was conducted in the four villages at the end of 1968. This was updated whenever the dietary-morbidity interviewers in their fortnightly home visits identified changes in household composition, new families (new marriages/unions or in-migrants), changes in residency within the village and out-migration. This updating of the census was verified by a cross-sectional census in 1974.

TABLE 4 Data collected in the INCAP longitudinal study, 1969-1977

Type of data	For whom (Target)	When collected	Where collected	By-whom	Collection dates
Supplement intake	Children 0-7 y and pregnant and lactating women	Everyday	Feeding Centers	Supplementation supervisors	1969-77
Morbidity, breastfeeding and menstruation recall	Children 0-7 y and pregnant and lactating women	every 15 days	Home	Dietary and Morbidity Interviewers	1969-77
Diet: 24-h recall in large villages and 72-h recall in small villages	Children 0-12 mo	Monthly	Home	Dietary	1973-77
	Children 15-36 mo	Every 3 mo	Home	Morbidity	1969-77
	Children 42-60 ma	Every 6 mo	Home	Interviewers	1969-77
	All pregnant women	Every trimester	Home	Dietary and morbidity interviewers	1969-77
	Lactating mothers
	0-12 mo	Every 3 mo	Home	Dietary	1969-77
	15-36 ma	Every 3 mo	Home	Morbidity interviewers	1973-77
	Other mothers	3, 6, 9 & 18 mo post partum	Home	Dietary and morbidity interviewers	1973-77
Birth weight, birth process and Apgar anthropometric indicators of nutritional status	Children 0-7 y	At birth	Home	Perinatologist	1969-77
	Children 15 d-24 mo	Every 3 mo	Clinic	Child Anthrop.	1969-77
	Children 30-48 mo	Every 6 mo	Clinic	Child Anthrop.	1969-77
	Children 60-84 ma	Every year	Clinic	Child Anthrop.	1969-77
	Pregnant and lactating women	During each trimester of pregnancy or lactation	Clinic	Maternal anthropometrist	1971-77
Hand-wrist x-rays	All children	At 3 mo. From 6 to 48 mo every 6 mo At 60, 72 and 84 mo	Clinic	Child anthropometrist	1969-77
Mental development Cognitive infant scale	Children 6-24 mo	At 6, 15 and 24 months	Test room in village	Psychometrist	1969-77
Preschool battery	Children 36-84 mo	Every year	Test room in village	Psychometrist	1969-77
Physicalexamination	Children 0-7y	15 d; 3 mo;1,3 and y	Clinic	Pediatrician	1971_77
Prenatal examinations	Pregnant women	Each trimester of pregnancy	Clinic	Auxiliary nurses	1969-77
Reproductive histories	Pregnant women	First prenatal examination	Clinic	Auxiliary nurses	1969-77
Records of visits to outpatient clinics	Children 0-7 y and pregnant and lactating women attending the medical clinic for any reason	For all visits for therapeutic care; Monday through Friday	Medical clinic	Auxiliary nurses	1971-77
Census and socioeconomic information	Families in community	Twice	Home	Census interviewers	1968-1969
Changes in household composition through census updates	Families in community	Every 15 days	Home	Dietary and morbidity interviewers	1968-1969
Father's anthropometry	Fathers of children in study	Once (cross-sectional)	Home	Child anthropometrist	1973-75
Retrospective life history of women (fertility, infant mortality and maternal employment)	Women 15-49 y ever in a marriage/union or ever a mother	Once (cross-sectional)	Home	Interviewer	1974-75
Income and wealth	Heads of household	Once (cross-sectional)	Home	Interviewer	1974-75
Attitudes and expectations of women	Women 15-49 y ever in a marriage/union or ever a mother	Once (cross-sectional)	Home	Interviewer	1975-76
Attitudes and expectations of men and retropective life history of men	One-half of the husbands of respondents to the "retrospective life history of women" and one-half of all single men	Once (cross-sectional)	Home	Interviewer	1975-76

The informant was the mother or other primary caretaker. Data collected included information about family structure, marital status, religion, number of pregnancies, number of children alive and relation of the nuclear family to the head of the extended family, and about ownership of items such as radios, sewing machines, refrigerators, bicycles and motor vehicles. Information about parental literacy was obtained through interviews and also through tests. Status (e.g., alive, dead, immigrated), birth order, kinship (e.g., father, son, adopted), parity (for mothers), schooling and occupation (for those older than 10 y) were recorded for each household member. Observations were noted about the house such as the types of walls, floor and roof, availability of electricity, type of water source and of grey water and feces disposal. Whenever a change occurred in the location of the home or in the status or kinship of a family member, the date of the change was noted.

Psychometric data. Full descriptions of the psychometric tests are given by Klein et al.(1977) and by Engle et al. (1992b). Neonates were tested within 10 d of birth. with the Brazelton Neonatal Scale and then at 6, 15 and 24 mo with an infant scale composed of items compiled from the Bayley, Cattell, Gesell and Merrill-Palmer Infant Scales. From 3-7 y of age the children were tested annually on a battery of 24 tests chosen to tap memory, language, perceptual reasoning, learning and abstract reasoning ability.

Supplementation. Supplementation and measurement of attendance and consumption began on January 1, 1969 in the large villages and on May 1, 1969 in the small villages. Attendance at the supplementation feeding station was recorded for all sample persons. The supplement was poured into cups calibrated to 180 ml. Cups were filled as often as requested. Individual intake was measured by recording the number of cups given and subtracting any leftover supplement measured to the nearest 10 mL.

All leftovers were poured into a large vessel. At the end of the serving period, the total amount recorded as ingested and the total amount served minus the volume of leftovers were compared. Calculations based on these data showed that reliability for supplement ingested was better than 99% per cup served. The reliability of concern in this study is of intakes during a week or longer periods; that reliability is almost perfect.

Home diet. Information on the home diets of children, pregnant and lactating women was collected according to the schedule indicated in Table 4. Daily home diet was estimated from 24-h recall surveys in the large villages and from 3-d recall surveys in the small villages. The amounts of food ingested were recorded in grams according to the usual INCAP recall method (Flores et al. 1970) and then converted to energy and nutrients using the INCAP food composition tables (Flores et al. 1960; Flores et al. 1971). The reliability of the dietary data was, however, found to be equally poor for both recall methods (División de Desarrollo Humano 1971, Habicht et al. 1974; Klein et al. 1973; Lechtig et al. 1976). Energy and protein had the highest reliabilities of all nutrients but these were only of the order of 0.15-0.30.

Medical care. Records of the presenting complaints, diagnoses and treatments were kept for all visits for use in the quality control system but, unfortunately, are no longer available. As of 1971, the symptomatology was recorded for each visit on the same form as the fortnightly morbidity data collected in the home and those data are available.

Morbidity, breast feeding and menstruation. Morbidity data were gathered every 14 d through retrospective interviews of mothers in the home by four home visitors, one for each village. The home visitors were rotated periodically among the four villages to offset interviewer bias. Interviews took place Monday through Friday, the families being so divided that routinely the entire population of each village was interviewed every 2 wk. During the interview, the mother was asked to recall any symptoms that she and any of her children younger than 7 years might have had in the previous 2 wk. Each subject's information was recorded in a separate questionnaire. The beginning and ending dates of a symptom were always noted. A routine quality-control system was applied allowing the method to be standardized, using a supervisor, and validated, using a physician. Information on menstruation in the mother (beginning and ending dates) were recorded or noted as absent in the morbidity questionnaire for the youngest child. Also noted was whether or not the child was breast fed.

To validate the morbidity survey, a physician examined children half a day after the morbidity visit without previously informing the morbidity interviewer. This study generally showed satisfactory sensitivities and specificities for the symptoms recorded. Sensitivity and specificity were 66% and 99%, respectively for diarrhea and 75% and 99% for fever (Martorell et al. 1975b).

A study of the prevalence of recalled symptoms over the 14 d between periodic surveys showed a fall in prevalence with respect to the day of interview indicating memory loss over the 2-wk period (Martorell et al. 1976). In spite of an average underreporting of 22%, diarrhea was nevertheless reported reliably enough to reveal statistically significant associations between percent of time ill with diarrhea and growth Martorell et al. 1975b; Schroeder et al. 1995).

Anthropometry. Body measurements were taken at specific ages by trained and standardized anthropometrists. A single person measured mothers throughout the study but three persons measured children at different times. All changes in personnel were preceded by rigorous standardization sessions.

The techniques of measurement are given in Martorell et al. (1982) and the quality control procedures used are described in Martorell et al. (1975a). Each week the data collected in the field were brought to the INCAP headquarters, computerized and analyzed. All children with values beyond two standard deviations from the agespecific means were remeasured for all variables to determine whether or not there had been an error in measurement, recording or punching. There was a weekly calibration of instruments, frequent standardization exercises for the anthropometrist at an urban orphanage and field replications. These exercises permitted the monitoring of precision and reliability; results of these exercises are given in Martorell et al. (1975a).

The anthropometry standardization method (Habicht 1974) is widely used today. Comparison of the reliability and precision achieved during the longitudinal study to results from others (Lehman et al. 1988; Marks et al. 1989;) speak favorably of the quality of the INCAP data.

Hand-wrist roentgenograms. The anthropometrist also took an X-ray of the left hand and wrist of children using a General Electric X-ray machine (model 100-15) set at 15 mA and 65 kV and using power from a gasoline generator. The X-ray head was set at 76 cm above the third metacarpal of the left hand with the fingers moderately splayed and the forearm placed at a right angle to the X-ray beam. Exposure was 48/60 of a second for children <2 y, and one second for older children. X-rays were taken at the ages specified in Table 4 concurrently with anthropometry.

Great care was taken to protect the children from stray X-rays. The X-ray film was placed in a lead lined box attached to the head of the X-ray machine. The seated child placed the hand into the box through a lead curtain. A film was placed on the child's seat and developed every month to be sure that there was no stray radiation.

The films were read for the number of ossification centers and the thickness of compact bone. Initially bone age also was determined according to the Tanner Whitehouse and the Greulich and Pyle methods. These detailed assessments were discontinued when analyses showed that the simple counting of ossification centers provided as much information (Yarbrough et al. 1973).

Physical examination. A pediatrician examined children at 15 d and at 3, 12, 36 and 84 mo of age to identify developmental and other problems and gave special attention to neurological function and minor anomalies indicative of congenital mental retardation or neurological impairment. This information would permit one to identify children whose association between less adequate nutrition and impaired mental development was probably due to the latter - impaired behavior leading to inadequate bonding and poor coping, both of which might result in malnutrition. It was also thought that the neurological data might reflect improved nutrition from the supplement. None of these data have been analyzed and published.