Dop, Marie-Claude

Milan, C.

N'Diaye, M.

Horizon / Pleins textes

Use of the multiple-day weighed record for Senegalese 
.children during the weaning period: a case of the 
“i nst ru m e n t effect 131 -3 
Marie-Claude Dop, Chantal Milan, Claude Milan, and A Makhtar NDiaye 
ABSTRACT In West Africa, the multiple-day weighed rec- 
ord is the most widely used technique for measuring children’s 
food intakes. The children’s eating behavior might be disrupted 
by the frequent weighings and the presence of a field-worker in 
the home. We explored the possibility of such an “instrument 
effect” in a 7-d food survey of 70 Senegalese children aged 
10-13 mo. Energy intakes decreased significantly during the 
food survey (P < 0.0001). The decrease affected both daytime 
breast milk intake (8%) and solid food intakes (15%). The chil- 
dren’s weight gain also decreased from a presurvey value of 
6.9 to 2.1 g.kg-’.wk-’, indicating that their intakes during the 
food survey were lower than their usual intakes. The food-sur- 
vey methodology was responsible for this “instrument effect.” 
Policy decision-makers should be aware that data collected with 
the multiple-day weighed record technique might not reflect 
African children’s usual food intakes. Am J Clin Nutr 
1994;59(~~ppl):266S-8S. 
KEY WORDS 
record, Senegal, weaning period 
Dietary methodology, multiple-day weighed 
Introduction 
The so-called “Hawthorne effect,” defined by Liu et al (1) as 
“the act of being measured influences behavior and reporting of 
behavior. . . ,” is often mentioned in the literature on dietary 
assessment methods. When such an instrument effect is present, 
measured food intakes do not reflect the subjects’ true intakes. 
As Todd et al (2) point out, when policy decisions are to be made 
on the basis of food intake data, the quality and relevance of the 
dietary information collected should be examined carefully. 
In developing countries, the multiple-day weighed record, 
based on the precise weighing technique, is the most widely used 
method for assessing children’s diets. Because of the low level 
of literacy, the presence of a field-worker in the home for the 
duration of the survey is often necessary. The survey is time 
consuming for mothers and the family’s usual dietary behavior 
might be disrupted. The possibility that an instrument effect 
might occur with this method has seldom been explored. Feno- 
Luzzi showed that no day-of-the-survey effect occurred in a 7-d 
weighed survey of adults in New Guinea (3). But in the literature 
on African children’s dietary intakes, we have found no mention 
of the instrument effect. 
The study reported here was part of a PI Fam of validation 
of dietary assessment techniques for estimat g Senegalese chil- 
dren’s food intakes during the weaning period. 
Subjects and methods 
The food survey technique was derived from the Food and 
Agricultural Organization (FAO) methodology (4). Solid foods 
eaten individually were weighed. When children were fed from 
the family common pot, mothers were asked to duplicate their 
child’s portion. Breast milk intake was measured by test-weigh- 
ing (5). 
The study took place in Pikine, the densely populated suburb 
of the capital, Dakar. Seventy children, 39 boys and 31 girls, 
aged 10-13 mo, participated in the 7-consecutive-day food sur- 
vey. Fifty families also agreed to a two-night survey. Fieldwork- 
ers were women of the same area with a high school education. 
They were instructed to be as unobtrusive as possible and the 
families were asked not to modify their eating behavior. The food 
composition table for West Africa and the FAO table for use in 
Africa were used to compute energy intakes (6, 7). In addition 
to the food survey, the children’s weight and morbidity were 
monitored weekly for a period of 2 mo. The food survey took 
place on week 5 of the study. 
Analysis of variance with a repeated-measures design was 
used to test day-of-the-week, day-of-the-food-survey and week- 
of-study effects (program 2V of BMDP; Bh4DP Statistical Soft- 
ware Inc., Los Angeles). The number of days of diarrhea and 
poor appetite per week were used as covariates of food intake 
and weight gain. Contrast analysis was used to compare partic- 
ular days or weeks. Results are given as means 2 SE. 
Results 
All the children were breast-fed, and all but two received solid 
foods regularly. The girls’ mean weight (8.4 ‘-c 0.7 kg) was lower 
From the Laboratoire de Nutrition Tropicale, ORSTOM, Montpellier, 
France; Registre Bourguignon des Tumeurs Digestives, Dijon, France; 
and Organisme de Recherche sur l’Alimentation et la Nutrition 
Africaines, Dakar, Senegal. 
’Supported in Part by the French Ministry of Research, grant 
8760517. 
3Address reprint requests to M-C Dop, Registre Bourguignon des 
Tumeurs Digestives, 7 boulevard Jeanne d’Arc, 21033 Dijon, France. 
2668 Am J Clin Nutr 1994;59(supp1):266S-SS. Printed in EX. 0 1994 American Society for Clinical Nutrition 
Q~STOM ~ m d s  ~ ~ ~ ~ m ~ ~ ~ a ~ ~ ~  
I 
A CASE OF "INSTRUMENT EFFECT" IN SENEGAL 
TABLE 1 
Energy intake by day of food survey* 
267s 
Day of survev 
1 2 3 4 5 6 7 P 
kJ.kg-l .&I 
Breast milk? 149.6 f 6.3 142.7 2 5.3 143.2 2 6.1 134.3 t 6.0 131.4 t 5.7 133.9 f 6.0 137.2 f 5.6 0.001 
Solid foods 116.7 f 9.6 121.7 f 11.6 114.1 i3 9.9 108.8 f 9.8 100.6 f 10.0 103.5 t 9.6 99.4 f 8.7 0.02 
All foods$ 266.3 f 10.3 264.4 2 10.3 257.3 rt: 8.5 243.0 2 8.8 232.0 f- 8.9 237.4 f 8.2 236.6 f 6.6 < 0.0001 
* i f SE; n = 70. ANOVA. 
t Daytime breast milk. 
-$ Solid foods and daytime breast mik. 
than that of the boys (8.9 2 1.0 kg, P = 0.04), but their overall 
weight gain was similar (6.8 ? 0.7 and 6.3 2 0.5 g.kg-'.wk-' 
for boys and girls, respectively, P = 0.66). The mean weekly 
prevalence of diarrhea was 23% and of poor appetite, 19%. 
Twenty-four-hour breast milk intake represented two-thirds of 
the energy intake. Total energy intake was similar in girls and 
boys: 344.3 k 15.4 and 348. 2 13.0 M.kg-'-d-', respectively 
(P = 0.86). Because no differences in food intakes or weight- 
gain were found between girls and boys in all the following anal- 
yses, results are presented for the sexes combined. 
Food intakes did not vary according to ethnic group, field 
worker, or date of survey. No day-of-the-week pattern of energy 
intake was found, either from breast milk (P = 0.82) or solid 
foods (P = 0.38). There was a significant day-of-the-food-survey 
effect (Table 1). Energy intake decreased regularly from day 1 
to 5. Daytime breast milk intake decreased until day 5 and then 
started to increase slightly on days 6 and 7, but did not regain its 
initial value (Fig 1). The mean number of daytime feedings de- 
creased from 7.7 ? 0.3 on day l to 6.2 4 0.3 on days 4-7. Energy 
intake from solid foods decreased regularly throughout the food 
survey (Fig 1). The overall decrease between the beginning and 
the end of the food survey amounted to 8% of daytime breast 
milk intake and 15% of solid food intake. When solid foods were 
analyzed according to the method of measurement, ie, weighing 
vs duplication, a significant decrease was observed for energy 
intake from weighed (P = 0.01) but not from duplicated foods 
160 I 1- BREASTMILK 
h 
I 
? 
7 
y" 
3 
a, 
Y m 
C 
c m 
Y 
4- .- 
8 
150 - 
140 - 
130 - 
120 - 
110 - 
100 - 
-t- SOLIDFOODS D 
90 ! I I I I I I I I 
1 2 3 4 5 6 7  
DAY OF FOOD SURVEY 
FIG 1. Mean energy intake from daytime breast milk and solid foods 
by day of the food survey. 
(P = 0.10). Nighttime breast milk intake also showed a day-of- 
survey effect as intake decreased sigmfìcantly between night 1 
(102.9 2 6.2 kJ/kg) and night 2 (90.4 2 5.8 kJ/kg) (P = ,O.Ol). 
Mean weight gain by week of study is shown in Fig 2. Sig- 
nificant variations were observed (P = 0.02). From week 1 to 
week 4, mean weight gain remained constant with minor nonsig- 
nificant fluctuations about a mean of 6.9 2 0.8 g.kg-'.wk-'. On 
week 5, the week of the food survey, mean weight gain dropped 
to 2.1 2 2.0 g.kg-**wk-'. There was an increase above the pre- 
survey level, indicating a period of catch-up growth, on week 7. 
Finally, on week 8 weight gain returned to the pre-food survey 
value. The comparison by contrast analysis of the presurvey 
weeks (1-4) to weeks 5 and 6 showed that weight gain was 
significantly lower during the food, survey and the following 
week (P = 0.01). 
Discussion 
This study was well accepted by the families. They were eager 
to participate because medical care and treatment were provided 
to the study children. None of the families dropped out. 
The observed decrease in intakes as the food survey proguessed 
can be interpreted as a measurement bias, ie, an underestimation 
of the actual intake of the children or can indicate a change in 
the children's diet during the food survey. The reduction in 
weight-gain observed at the same time as the food survey indi- 
cates that children's intakes were in fact lower than their usual 
1 2 3 4 5 6 7 0  
WEEK OF STUDY 
FIG 2. Mean weight gain by week of study. The food survey took 
place on week 5 (ANOVA week-of-study effect, P = 0.02). 
2688 DOP ET AL 
intakes. This finding clearly demonstrates that the decrease in 
intakes was due to an instrument effect. It is difficult to say what 
the magnitude of the decrease was, compared with the children’s 
usual intake, but it was important enough to cause a 70% reduc- 
tion in weight-gain compared with the presurvey weeks. This 
“Hawthorne effect” did not depend on the field workers. It was 
caused by the food survey methodology itself. 
Why the 7-d weighed record decreased the children’s intake is 
difficult to analyze. Daytime breast milk intake declined because 
of a reduction in the number of daytime feeds. Senegalese moth- 
ers breast-feed on demand and often use breast-feeding for its 
soothing effect when the child is not hungry. It is possible that 
to reduce the number of weighings, the mothers tended to feed 
the children only when they felt that they were obviously hungry. 
The observation that, after the first 5 d of the food survey, the 
breast milk intake increased slightly, although the number of 
feeds remained low, suggests that children adapted to the new 
pattern of feeding. Solid food intakes were more sensitive to the 
instrument effect than breast milk intake. How they were af€ected 
by the implementation of the food survey is less clear. The ab- 
sence of a significant instrument effect for duplicated foods is 
difficult to interpret because intake from the family common pot 
was highly variable within subjects. Finally, whether the instru- 
ment effect changed intakes of solid food only quantitatively or 
also qualitatively cannot be inferred from these data. 
The overly demanding design of the food survey could explain 
by itself why an instrument effect occurred. But data from an- 
other simplified survey of shorter duration, also using the precise 
weighing technique and performed in the same community, dem- 
onstrated a comparable effect. The study lasted 2 consecutive 
days and only solid foods were weighed. Energy intake decreased 
significantly between the fist and the second day (8). These find- 
ings raise the question of whether the instrument effect is inherent 
to the multiple-day weighed record. Policy decision-makers 
should be aware that data based on the multiple-day weighed 
, ,  
l e t  
i \  
record might not reflect African children’s true dietary intake. 
Policy decisions should not be based solely on data collected with 
this technique. Short-term recall methods could be used concur- 
rently for assessing intake of solid foods. The precise weighing 
technique should not be taken as a “gold standard” for the mea- 
surement of habitual intake. It would be interesting to reexamine 
earlier surveys on African children in the light of our findings. 
Analysis of dietary survey data should include the detection of 
an instrument effect. When study subjects are children, data on 
weight-gain can be a sensitive indicator of the presence of such 
We thank S Chevassus-Agnes for his guidance, L Papoz for her val- 
an effect. El 
uable methodologic suggestions, and N Senne for the laboratory work. 
References 
1. Liu K, Stander J, Dyer A, Mc Keever J, Mc Keever P. Statistical 
methods to assess and minimize the role of intra-individual vari- 
ability in obscuring the relationship between dietary lipids and serum 
cholesterol. J Chon Dis 1978;31:399-418. 
2. Todd K, Hudes M, Howes Calloway D. Food intake measurement: 
problems and approaches. Am J Clin Nutr 1983;37:139-46. 
3. Ferro-Luzzi A. Energy intakes as predictors of energy balances in 
free-living populations. In: Pollitt E, Amanti P, eds. Energy intakes 
and activity. New York: Liss, 1984:79-99. 
4. Reh E. Manual on household food consumption studies. Rome: Food 
and Agricultural Organization of the United Nations, 1962. 
5. World Health Organization. The quantity and quality of breast milk. 
Geneva: WHO, 1985. 
6. Organisme de Recherche sur l’Alimentation et la Nutrition Afri- 
caines (ORANA). Food composition table for West-Africa. Dakar, 
Senegal: ORANA, 1982 (in French). 
7. Food and Agriculture Organization. Food composition table for use 
in Africa. Rome: FAO, 1968. 
8. Dop MC, Milan C, Milan CI, N’Diaye AM. Validation of the 24- 
hour recal1 for measuring Senegalese children’s food intakes at the 
age of weaning. Gastro Clin Bio1 1992;16A299(abstr)(in French). 


Use of the multiple-day weighed record for Senegalese children during the weaning period : a case of the "instrument effect"1-3

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