Question

Many interventions studies have shown that mosquito nets treated with insecticide can reduce the morbidity and mortality from malaria in young children in Africa. However, Abdulla et al. (2001) were interested in whether countries that have implemented programs to supply these treated nets to communities with a high prevalence of malaria have seen the benefits highlighted by the intervention studies. In 1977 investigators carried out a cross-sectional study of children less than 2 years of age in 18 villages in Tanzania at the beginning of a marketing campaign to promote the use of treated nets. They collected data on net ownership and other factors by questionnaire (the mothers of the children were interviewed), and took blood samples from the children in the study to assess whether they were infected with malaria parasites (parasitaemia), and also to see whether they were anemic (as a consequence) . The children were also assessed for clinical signs of malaria. Two further surveys were done over the next 2years. A different random sample of children was selected on each occasion.

The investigators identified 985 eligible children, and interviewed the mothers of 827 of these children over the course of the three cross-sectional surveys (16 mothers refused consent, and 142 could not be contacted). Of the 827 interviewees, data from 748 were included in the analysis because 68 children were aged over 2 years at the time of sampling and net status was not known for 11 children.

The following table shows some of the results from the study.

Table1:

	Year of Survey
	1977	1998	1999
Number of eligible children	325	330	330
Number of children analyzed	240	269	239
Number (%) with no net	100 (42%)	49 (18%)	40 (17%)
Number with untreated net	116 (48%)	64 (24%)	53 (22%)
Number with treated net	24 (10%)	156 (58%)	146 (61%)
Number (%) of children with anemia	118 (49%)	83 (31%)	62 (26%)
Number (%) with parasitaemia	151 (63%)	126 (47%)	90 (38%)
Number with splenomegaly	207 (86%)	144 (54%)	117 (49%)

Source: data from Abdulla et, al. (2001)

Answer the following questions about this study

Q1: Is this a descriptive or analytical cross sectional study? Give a reason for your answer (2pt)

Q2: Does it matter that data from some of the eligible children were not included in the analysis? (2pts)

Q3: Describe the results of the study shown in the above table. (2pts)

Q4: Can you calculate the effect of net ownership on the proportion of children with malaria parasitaemia from the table? Why? (2pts)

Answer 1

Q1:

Answer: Cross sectional study

Reason:

Cross sectional study is a observational study that analysis data from population at specific points of time.

Q2:

1.Yes, In analysis some eligible samples are not included.

2.985 samples are eligible, but in analysis only 748 samples are included.

Q3:

1.In 1997 the anemia children's are 49%, then it reduced 31% in 1998, and further reduced as 26℅ in 1999.

2.In 1997 the parasiteamia 63℅, then it reduced 47% in 1998, then further reduced in to 38℅.

Q4:

Net ownership= number of parasitaemia/ Total number of cases× 100

= 387/985×100

= 39.28℅.