Parameters associated with design effect of child anthropometry indicators in small-scale field surveys.

BACKGROUND: Cluster surveys provide rapid but representative estimates of key nutrition indicators in humanitarian crises. For these surveys, an accurate estimate of the design effect is critical to calculate a sample size that achieves adequate precision with the minimum number of sampling units. This paper describes the variability in design effect for three key nutrition indicators measured in small-scale surveys and models the association of design effect with parameters hypothesized to explain this variability. METHODS: 380 small-scale surveys from 28 countries conducted between 2006 and 2013 were analyzed. We calculated prevalence and design effect of wasting, underweight, and stunting for each survey as well as standard deviations of the underlying continuous Z-score distribution. Mean cluster size, survey location and year were recorded. To describe design effects, median and interquartile ranges were examined. Generalized linear regression models were run to identify potential predictors of design effect. RESULTS: Median design effect was under 2.00 for all three indicators; for wasting, the median was 1.35, the lowest among the indicators. Multivariable linear regression models suggest significant, positive associations of design effect and mean cluster size for all three indicators, and with prevalence of wasting and underweight, but not stunting. Standard deviation was positively associated with design effect for wasting but negatively associated for stunting. Survey region was significant in all three models. CONCLUSIONS: This study supports the current field survey guidance recommending the use of 1.5 as a benchmark for design effect of wasting, but suggests this value may not be large enough for surveys with a primary objective of measuring stunting or underweight. The strong relationship between design effect and region in the models underscores the continued need to consider country- and locality-specific estimates when designing surveys. These models also provide empirical evidence of a positive relationship between design effect and both mean cluster size and prevalence, and introduces standard deviation of the underlying continuous variable (Z-scores) as a previously unexplored factor significantly associated with design effect. The magnitude and directionality of this association differed by indicator, underscoring the need for further investigation into the relationship between standard deviation and design effect.

The PROBIT approach in estimating the prevalence of wasting: revisiting bias and precision.

BACKGROUND: The PROBIT methodology was presented in the 1995 World Health Organization Technical Report on Anthropometry as an alternative to the standard prevalence based method of measuring malnutrition in children. Theoretically the PROBIT method will always give a smaller standard error than the standard prevalence method in measuring malnutrition. A recent article by Dale et al. assessed the PROBIT method for measuring global acute malnutrition measure and found that the method was biased and the precision was superior only for sample sizes less than 150 when compared to the standard method. In a manner similar to Dale, our study further investigated the bias and precision of the PROBIT method for different sample sizes using simulated populations. RESULTS: The PROBIT method showed bias for each of the ten simulated populations, but the direction and magnitude of the average bias was changed depending on the simulated population. For a given simulated population, the average bias was relatively constant for all sample sizes drawn. The 95% half-width confidence interval was lower for the PROBIT method than the standard prevalence method regardless of the sample size or simulated population. The absolute difference in the confidence limits showed the most gains for the PROBIT method for the smaller samples sizes, but the ratio of confidence intervals was relatively constant across all sample sizes. CONCLUSIONS: The PROBIT method will provide gains in precision regardless of the sample size, but the method may be biased. The direction and magnitude of the bias depends on the population it is drawn from.

Shipshape: sanitation inspections on cruise ships, 1990-2005, Vessel Sanitation Program, Centers for Disease Control and Prevention.

In the course of a successful collaboration between the Centers for Disease Control and Prevention (CDC) and the cruise ship industry on reducing common-source outbreaks, CDC's Vessel Sanitation Program (VSP) has expanded its training, education, and cruise ship inspection programs. The study reported here evaluated 15 years of ship sanitation inspection data from the National Center for Environmental Health and assessed performance in specific sanitation categories from 1996 to 2005. During the period 1990-2005, scores from cruise ship environmental sanitation inspections steadily improved. The percentage of inspections with violations decreased among five of nine categories. Those five categories were Washing Facilities, Contact Surfaces, Facility Maintenance, Food Handling, and Communicable Disease Practices. Inspection violations increased proportionally in the categories of Swimming Pools and Water System Protection/Chart Recording. Overall continued good performance in most sanitation categories is likely attributable to on-site training during inspections, improvements in ship construction, and a switch from hot-holding temperatures to time limits as a public health control for foods on display.

Epidemiology of gastroenteritis on cruise ships, 2001-2004.

BACKGROUND: The incidence of diarrheal disease among cruise ship passengers declined from 29.2 cases per 100,000 passenger days in 1990 to 16.3 per 100,000 passenger days in 2000. In 2002, the Vessel Sanitation Program of the Centers for Disease Control and Prevention reported 29 outbreaks (3% or more passengers ill) of acute gastroenteritis on cruise ships, an increase from 3 the previous year. This analysis of gastroenteritis on cruise ships, conducted in 2005, details the increase in outbreak incidence rates during 2001 through 2004. METHODS: Using Gastrointestinal Illness Surveillance System data, investigators evaluated incidence rates of gastroenteritis on cruise ships calling on U.S. ports, carrying 13 or more passengers, by cruise length and reporting region during the study period. The investigators also evaluated the association between inspection scores, and gastroenteritis incidence and the frequency of outbreaks in 2001 through 2004. RESULTS: During the study period, the background and outbreak-associated incidence rates of passengers with acute gastroenteritis per cruise were 25.6 and 85, respectively. Acute gastroenteritis outbreaks per 1000 cruises increased overall from 0.65 in 2001 to 5.46 in 2004; outbreaks increased from 2 in 2001 to a median of 15 per year in 2002-2004. Median ship inspection scores remained relatively constant during the study period (median 95 on a 100-point scale), and were not significantly associated with either gastroenteritis incidence rates (risk ratio, 1.00; 95% confidence interval, 0.98-1.02) or outbreak frequency (Spearman's coefficient, 0.01, p=0.84). CONCLUSIONS: Despite good performance on environment health sanitation inspections by cruise ships, the expectation of passenger cases of gastroenteritis on an average 7-day cruise increased from two cases during 1990-2000 to three cases during the study period. This increase, likely attributable to noroviruses, highlights the inability of environmental programs to fully predict and prevent risk factors common to person-to-person and fomite spread of disease.

Physical activity, sports participation, and suicidal behavior among college students.

PURPOSE: To evaluate the relationship between physical activity, sports participation, and suicidal behavior among college students (N = 4,728). METHODS: Data from the 1995 National College Health Risk Behavior Survey were analyzed. Students were classified as engaging in frequent vigorous activity 6-7 d.wk-1, vigorous activity 3-5 d.wk-1, moderate activity, low activity, or no activity. Sports participation was dichotomized into "yes" or "no" participation. Suicidal behavior was defined as thoughts about, plans for, or attempts at suicide during the 12 months before completing the survey. Data were stratified by sex and multivariable logistic regression modeling, calculated odds ratios (ORs) (adjusted for age, race/ethnicity, Body Mass Index/weight perception, cigarette smoking, episodic heavy alcohol use, drug use, and either activity level or sport participation) for suicidal behavior as associated with physical activity and sports participation. RESULTS: Adjusted ORs show that men in the "low activity" group were at almost half the odds (adjusted OR = 0.54; P < 0.015) of reporting suicidal behavior than men in the "not active" group. Women who engaged in moderate or frequent vigorous activity were at greater odds of reporting suicidal behavior compared with inactive women; OR = 1.76 (P < 0.035) and 1.99 (P < 0.034) respectively. Sports participation was protective against suicidal behavior. Adjusted ORs show that men who did not participate in sports were 2.5 times (P < 0.0003) more likely to report suicidal behavior than men who were sports participants. Women not participating in sports had 1.67 times the odds of reporting suicidal behavior than women sports participants (P < 0.05). CONCLUSIONS: Associations were found between sports participation/selected patterns of physical activity and suicidal behavior. Causal factors mediating the relationships need to be identified.