ABSTRACT
BACKGROUND: Repeating a QC that is outside 2SD from the mean (1:2s rule) appears to be a common practice. Although this form of repeat-sampling is frowned on by many, the comparative power of the approach has not been formally evaluated. METHODS: We computed power functions mathematically and by computer simulation for 4 different 1:2s repeat-sampling strategies, as well as the 1:2s rule, the 1:3s rule, and 2 common QC multirules. RESULTS: The false-rejection rates for the repeat-sampling strategies were similarly low to those of the 1:3s QC rule. The error detection rates for the repeat-sampling strategies approached those of the 1:2s QC rule for moderate to large out-of-control error conditions. In most cases, the power of the repeat-sampling strategies was superior to the power of the QC multirules we evaluated. The increase in QC utilization rate ranged from 4% to 13% for the repeat-sampling strategies investigated. CONCLUSIONS: The repeat-sampling strategies provide an effective tactic to take advantage of the desirable properties of both the 1:2s and 1:3s QC rules. Additionally, the power of the repeat-sampling strategies compares favorably with the power of 2 common QC multirules. These improvements come with a modest increase in the average number of controls tested.
Subject(s)
Computer Simulation , Imidazoles , Nitro CompoundsABSTRACT
The aim of present study is to compare Afghan refugees and Iranian residents in terms of their knowledge, attitude and practice concerning malaria transmission and protection in an endemic area in Southeast Iran. This cross sectional study was conducted over a period of 10 months [2004-2005] and involved a total of 775 people, including Iranian and Afghan subjects. The age range of participants was 15 to 55 years. Data collection was done through a structured questionnaire consisting of open and close questions and comprising several, namely personal characteristics details, history of malaria infection and treatments, type of residence, mobility, self protection, facilities, and access to health services. Both Iranians and Afghans were familiar with the three typical symptoms of the disease [fever, chills and muscle aches]: 67.1% of Iranians and 78% of Afghans were able to name least one of the three typical symptoms. In both groups the majority of subjects were aware that malaria transmission occurs through mosquito bite but there was a significant difference regarding knowledge of malaria transmission [CHI2 = 142.2, P<0.001]. Chi-square test for goodness of fit showed that the distribution of symptom indicators is significantly different between the two groups. For Iranians, the most important source of information about malaria was the health facilities [44.5% of the total] while most Afghans [65.3%] had obtained the information through friends and relatives. In both groups, the mass media had acted as the source of information in only 3.4%. Altogether, 24% of the participants reported the use of mosquito bed nets; almost 90% of Afghans and 62% of Iranians said that they did not used bed nets at all. However, the number of Iranians who used bed nets was four times greater than the Afghans who did so. Although the majority of subjects were familiar with malaria transmission and protection methods, they largely neglected safety precautions. Moreover, it seems that the high prevalence of malaria among Afghans is due to their life style rather than cross-border travel. The study also revealed that Afghan people have poor communication with the local health facilities, a point that must receive special attention in future malaria control programs