Data collection in an inland water fishery (Jebba Lake, Nigeria): the trade-off between cost and accuracy

Accurate and long-term fisheries data are vital for fisheries managers to understand and manage fisheries effectively. Only a few inland waters have such data. This is often due to the difficulty and high cost as well as low priority given by governments to data collection activities. Besides accuracy, practicality and cost are also important considerations when designing fishery data collection systems. A data set from the fishery of Jebba Lake in Niger State, North-central of Nigeria, was used to assess how low cost, yet accurate, fisheries data collection can be achieved. Simulations of reducing the frequency of the annual inventory of fishery manpower and crafts (frame survey) and of lowering the sampling effort of monthly fish catch and fishing activities (catch assessment survey) were made. The effect of the reductions on daily catch, fishing activity and yield estimate was then determined. Reducing the number of sampling days was reduced from four to two per month. Problems of obtained accurate and long-term fisheries data from tropical inland waters were discussed

On A New Method Of Bias Reduction: Alternative To Approximately Unbiased Ratio Estimators

This paper proposes a new method of bias reduction from order n^-1 to order n^-2 resulting in a new approximately unbiased ratio estimator. The efficiency of this estimator for the ratio of population means of two characters is compared with the existing six other Ratio estimators under a linear regression model. Keywords: Approximately Unbiased, Mean Square error, Efficiency, Regression model, Ratio Estimator,Bias,Auxiliary Variabl

A Two-way Randomized Response Technique in Stratification for Tracking HIV Seroprevalence

Seroprevalence surveys of HIV pandemic are highly sensitive especially in Africa. The objective of this study is to reach research frontier to devise a two-way randomized response model (RRM) in stratification and use same to estimate HIV seroprevalence rates in a given population and compare results with the existing seroprevalence rates. The randomized response techniques (RRT) guarantees the anonymity of respondents in surveys aimed at determining the frequency of stigmatic, embarrassing or criminal behaviour where direct techniques for data collection may induce respondents to refuse to answer or give false responses. The motivation was to improve upon the existing RRMs as well as to apply them to estimate HIV seroprevalence rates. Warner proposed the pioneering RRM for estimating the proportion of persons bearing a socially disapproved character. Quatember produced unified criteria for all RRTs, Kim and Warde proposed a stratified RRM and so many others. The proposed two-way RRM in stratification for HIV seroprevalence surveys was relatively more efficient than the Kim and Warde stratified estimator for a fixed sample size. The chosen design parameter was 0.7, using the criteria of Quatember who derived the statistical properties of the standardized estimator for general probability sampling and privacy protection. Furthermore, the model was used to estimate the HIV seroprevalence rate in a sampled population of adults 3,740 people aged 18 years and above attending a clinic in Kaduna, Nigeria using a sample size of 550. The findings revealed that HIV seroprevalence rate, as estimated by the Model, stood at 6.1% with a standard error of 0.0082 and a 95% confidence interval of [4.5%, 7.7%]. These results are consistent with that of Nigerian sentinel survey (2003) conducted by NACA, USAID and CDC which estimated the HIV seroprevalence in Kaduna State as 6.0%. Hence, the RRTs herein can serve as new viable methods for HIV seroprevalence surveys. Key words Randomized response techniques, two-way randomized response models, seroprevalence rates, design parameter, efficiency, sentinel surveys, stratified random samplin

Rao, Hartley, and Cochran’s Sampling Scheme: Application

This paper takes a look at the Rao, Hartley, and Cochran’s sampling scheme, when it is required to select sample of sizes 4, 6, 12, and 18 with probability proportional to size without replacement sampling (unequal probability sampling without replacement). This is done by using the data from the 2008 Nigeria Demographic and Health Survey (NDHS). We studied the distribution of women age 15 – 49 years employed in the 12 months preceding the survey by type of employer. Here, we considered self-employed women alone. It is shown how sample of sizes 4, 6, 12, and 18 could be randomly selected from the population of size 36.  Population total and variance were computed with confidence interval constructed for the population total. For the randomly selected states in this paper, we realized that as the sample size increases, the variance and standard error decreases. Keywords: Rao, Hartley, and Cochran’s sampling scheme, probability proportional to size without replacement, sample size four, six, twelve, eighteen

Nonresponse and ratio estimation problems in sample surveys

SIGLEAvailable from British Library Document Supply Centre- DSC:D81922 / BLDSC - British Library Document Supply CentreGBUnited Kingdo