Confidence alt text

The diagram is an output from iNZight Confidence Interval Coverage Module. There are three graphs, all with identical scales from 10 – 40 marked in 5’s. 

The top graph, labeled Population, shows a dot plot and a box plot of the population of 500 right foot lengths from the Census at School database. The grey dots are stacked in bars with an approximately normal shape, except the 24 cm bar is slightly lower than the 23 cm and 25 cm bars. Minimum is 10 cm, lower quartile is 22 cm, median 23 cm, upper quartile 25 cm, maximum 45 cm. Overlaid on the population are black dots showing the last sample selected from the population. There is a purple vertical line on the graph showing the mean of the population, approximately 23.43 cm. 

The sample (n = 30) is graphed below the population. The dot plot has 30 values, one of each unless indicated, (14, 17, 20 (2), 21, 22 (8), 23 (2), 24 (2), 25 (7), 26 (4), 36 and 40.  A box plot is drawn below the dot plot, minimum 14 cm, lower quartile 22 cm, median 23.5 cm, upper quartile 24 cm and maximum 40 cm. A blue line showing the sample mean is marked and there is an orange bar showing a confidence interval based on this sample. 

Confidence Interval History is the third graph. It shows the last 40 of 1000 confidence intervals calculated. The confidence intervals are closely packed horizontal lines: green if the interval covered (contained) the population mean and red if not. There are 3 red intervals, 2 together at about 12 down from the top and 1 at about 30 from the top. The intervals, all within 21 cm and 27 cm, appear to vary randomly in width and centre. To the left of the intervals is a text box containing the words: Coverage: 947 out of 1000 94.7%. 

Last updated September 24, 2013

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