Mathematical Methods · Unit 4 · Sampling and proportions · Random sampling
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A university wants to estimate the average weekly study hours of its \(15{,}000\) enrolled students. A researcher stands outside the main library during evening hours and surveys the first 120 students who exit the building. Which of the following best describes the primary source of bias in this sampling method?
A market research company plans to survey 150 shoppers about their favourite supermarket. The shopping centre has four major supermarkets: SuperMart (800 customers per week), FreshStore (600 customers per week), ValueBuy (400 customers per week), and LocalGro (200 customers per week). The company decides to use stratified random sampling to ensure the sample is representative. (a) Identify the source of bias if the company instead selected all 150 shoppers from SuperMart only. (1 mark) (b) Calculate the number of shoppers from each supermarket that should be selected using stratified random sampling. (2 marks)
A researcher wishes to estimate the proportion of households in a city that own electric vehicles. Which sampling procedure is most likely to introduce bias?