ch11 - 1 Ch 11 Chance Errors in Sampling A health study is...

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Unformatted text preview: 1 Ch 11 Chance Errors in Sampling A health study is done on a representative cross section of 4,738 adults The researcher can sample only 100 of them Our question is whether the sample is representative? Assume the population had 3,032 (64%) male Then we might pick … F F M F M F F M F M M F M M M M F M M M M F M F M M F M F M M M F F M M M F F M M M M F M M M M F M M F M M F M F M M F M F M M M M F M M M M M M M F M M M M F M F M M F M F M M F M M F M M M M F M M F F F M M F F F M M M F M M F M F M M F F M M F M F M M F M M F M M F M F M M F M F M M M M F M M M F F M F F F F M F F M F M F M M F M F M F F M M F F F M M F M M M M F M M M M F M M M F M M M M F M ( M=63, F=37) 2 • Repeat i ng t hi s 250 t i mes … Repeat i ng t hi s 250 t i mes … 63 59 64 70 71 66 71 61 65 65 74 65 62 68 65 69 74 65 62 62 59 59 64 68 57 67 60 60 60 65 65 58 72 66 65 66 65 68 68 63 57 59 61 63 67 63 55 61 69 69 59 60 64 66 59 65 67 63 56 58 61 67 63 61 65 61 62 65 64 69 67 65 65 68 66 59 65 62 63 67 68 51 63 62 68 65 69 63 59 61 68 69 75 67 65 62 63 60 65 67 64 71 66 65 60 65 64 65 68 59 66 71 64 66 57 59 60 61 61 61 63 60 70 73 66 66 70 66 67 63 63 60 60 56 62 68 71 64 66 57 58 66 66 62 73 70 62 60 64 72 66 65 72 63 62 66 61 64 59 58 58 68 67 74 63 66 60 66 62 67 65 64 58 66 59 68 64 65 66 64 63 70 58 55 54 70 58 60 74 63 63 73 65 61 66 60 62 70 66 66 63 58 60 64 58 61 59 54 61 55 64 65 64 66 58 68 66 62 69 65 67 69 62 61 65 68 73 68 58 58 62 72 65 69 61 65 72 64 70 67 63 67 62 66 63 58 64 67 69 72 • We got 64 onl y 18 t i mes We got 64 onl y 18 t i mes - pr obabi l i t y - pr obabi l i t y of get t i ng exact l y 64 mal es i n our sampl e of get t i ng exact l y 64 mal es i n our sampl e i s pr et t y l ow ( i . e. 18/ 250) i s pr et t y l ow ( i . e. 18/ 250) 3 The proportion of male in the population remains at 64%, but the proportion in the sample varies due to chance error . Below is a histogram of the number of men from the samples of size 100 persons (i.e. 250 repetitions) cf . Ker r i ch exper i ment ; Chance var i abi l i t y i n sampl i ng j ust l i ke chance var i abi l i t y i n coi n t ossi ng. 5 10 15 49 52 55 58 61 64 67 70 73 76 è - ª % No. men 4 What if we increase the sample size from 100 to say 400? Following the LAW of AVERAGES, as sample size increases, chance error in percentage decreases. percentage in sample = percentage in population + chance error The bigger the sample, the closer the sample proportion to the population proportion....
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ch11 - 1 Ch 11 Chance Errors in Sampling A health study is...

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