muddying the waters r1.pdf

# There is a negative correlation the number of

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There is a negative correlation. The number of visitors ranges from 70 to 78, a range of 8 with a mean average of 75. The noise level ranges from 10 to 60 decibels, with a range of 50 decibels and a mean average of 35 decibels 1 . Interpreting the pie chart: The number of campers surveyed was 50. 80% of the sample responded yes, 16% unsure, and 4% no. The numbers of respondents are 40, 8, and 2 respectively. Question 2: The camp manager’s argument is biased in several ways. Her choice of math introduces bias: The scatter plot has a misleading scale. The scale on the ‘number of campers’ axis starts at 40 rather than 0. It gives the impression that correlated with the rise in noise level there has been a large drop in visitor numbers. The number of campers only varies by 8 across the fourteen-day period, decreasing by about 10% between the quietest and noisiest day. The survey statement and question is biased. Stating that the noise is ‘loud’ and assuming that the respondent can hear the noise pushes the respondent towards a positive response; the use of ‘spoiling enjoyment’ in the question also introduces potential bias. The pie chart is based on a relatively small sample (50 campers). The survey took place on one day. On only 2 days on the scatter chart were there 50 campers. Both days were particularly noisy. Surveying only on a noisy day produces potential bias in the survey responses. It would have been helpful to show the number of respondents, not just percentages, on the pie chart, to aid interpretation of the results. Her interpretations of her data and statistics are incorrect. Peggy claims that the noise from the turbines has caused a drop in camper numbers. The correlation between the noise level in decibels and the number of campers does not show there is a causal relationship between the two variables. There may be other explanations of why the number of campers and the noise level correlate. For example, the turbine noise increases with the wind level, so you would expect fewer people to want to camp at noisy times, because it is windier then.

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Teacher guide Interpreting Data: Muddying the Waters T-12 Although most of the people surveyed did state that the wind turbines spoilt their enjoyment, the questionnaire was biased, the sample was small, and the survey took place on a noisy day. As the results of the survey are dubious, there is no evidence to support Peggy’s interpretation that most people coming to the camp would agree with the results of the survey. She cannot generalize from a small, biased sample and she cannot rely on responses to a biased question. 1 From the US Environmental Protection Agency website: The document identifies a 24-hour exposure level of 70 decibels as the level of environmental noise which will prevent any measurable hearing loss over a lifetime. Likewise, levels of 55 decibels outdoors and 45 decibels indoors are identified as preventing activity interference and annoyance.
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