This section describes how to use SAS to estimate mean food intakes along with standard errors. To illustrate this, consumption of milk is used as an example. As explained in the key concepts section, there are different ways to group foods for analysis, and so it is with examining “milk” intakes. One way is to consider only fluid milk reported separately—not as part of a combination—and another is to account for all milk and milk products—including milk, yogurt and cheese—whether reported separately or as part of a combination or mixture. In the programs that follow, consumption of fluid milk not in combination, measured in grams, and consumption of all milk and milk products, measured in cup equivalents, are used as examples.
The following analyses are for children ages 6-11, and mean intakes are estimated among users. Such estimates answer the question: on average, what quantity is consumed in a given day by users of the food? Analysts interested in per capita consumption (that is, including zeroes for non-consumers) would need to specify that missing values should be set to zero. See full program under Additional Resources for note about this.
Sorting is not a necessary first step in SAS, as it is in SUDAAN. Therefore, properly weighted estimated means and standard errors can be obtained via a single SAS procedure, PROC SURVEYMEANS.
In the sample below, the NOBS, MEAN, and STDERR options in the PROC SURVEYMEANS statement request that the number of observations, the estimated mean, and its estimated standard error, respectively, be printed for each analysis variable. The DOMAIN statement designates the combination of variables required to obtain separate estimates by gender (RIAGENDR) within the cohort of interest (INCOH). INCOH is a variable that has value 1 if the individual is “in the cohort” and zero otherwise. Here, children ages 6 to 11 with complete and reliable recall data have INCOH=1. The FORMAT statement controls how levels of the RIAGENDR variable are printed on the output. As in the SUDAAN example above, the weight variable being used is for the dietary recall Day 1 subsample (WTDRD1).
* Use the PROC SURVEYMEANS procedure in SAS to compute properly weighted ;
* estimated means and standard errors ;
* To properly perform a subdomain analysis, form a 2-way table of INCOH ;
* by RIAGENDR. In this example, the statistics of interest are those ;
* where INCOH=1 in the table. ;
var MILK0 D_TOTAL;
format RIAGENDR GENDER. ;
title1 "Estimated daily intake of fluid milk drunk by itself as a beverage;
and of total milk and milk products" ;
title2 "children age 6-11, WWEIA, NHANES 2003-2004 - using SAS" ; ;
Estimated daily intake of fluid milk drunk by itself as a beverage;
children age 6-11, WWEIA, NHANES 2003-2004 - using SAS The SURVEYMEANS Procedure
Data Summary Number of Strata 15
Number of Clusters 30
Number of Observations 10122
Number of Observations Used 9034
Number of Obs with Nonpositive Weights 1088
Sum of Weights 286222757
Statistics Std Error
Variable Label N Mean of Mean ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ
MILK0 Fluid milk (g) consumed outside of a combination for consumers 2332 451.443365 12.905530
D_TOTAL Total number of milk group (milk, yogurt & cheese) cupequivalents 8273 1.761007 0.048017
Domain Analysis: Gender - Adjudicated*INCOH Gender - Std Error Adjudic. INCOH Variable Label N Mean of Mean ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ Male 0 MILK0 Fluid milk (g) consumed outside of a combination for consumers 1034 503.310228 22.624207 D_TOTAL Total number of milk group (milk, yogurt & cheese) cupequivalents 3615 1.916645 0.059658 1 MILK0 Fluid milk (g) consumed outside of a combination for consumers 143 395.289004 45.893677 D_TOTAL Total number of milk group (milk, yogurt & cheese) cupequivalents 422 2.595515 0.162629 Female 0 MILK0 Fluid milk (g) consumed outside of a combination for consumers 984 426.001838 13.414503 D_TOTAL Total number of milk group (milk, yogurt & cheese) cupequivalents 3758 1.500916 0.048613 1 MILK0 Fluid milk (g) consumed outside of a combination for consumers 171 305.434366 27.785526 D_TOTAL Total number of milk group (milk, yogurt & cheese) cupequivalents 478 2.133974 0.141756 ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ
Highlights from the output include:
It is important to note that the analysis above was conducted using only children ages 6-11 who were consumers of milk as a beverage. If, however all members (i.e. consumers and non-consumers) of the selected age group were included (total n = 900; 422 males and 478 females), then the average amounts would be lower. For males, the mean milk intake would be 145 gm and for females, it would be 136 gm (see the full Milk program in the Additional Resources section for example code). These means represent the per capita consumption.