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Chapter 8 Notes (5)

# Chapter 8 Notes (5) - o The t-distribution is bell shpaed...

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Unformatted text preview: o The t-distribution is bell shpaed and symmetric about 0. o The probabilities depend on the degrees of freedom, df = n — 1. The t-distribution has a slightly different shape for each distinct value of df, and different t—scores apply for each df value. c The t-distribution has thicker tails and is more spread out than the standard normal distribution (z-distribution). c When df is 30 or more, the t—distribution is nearly identical to the z-distribution. ......._,V, __. ., M W e... N we '; Skunk-2d Normal Distribution Ale“ spread out than 1 dimi'mmm I Diiulbulloﬂ. (if: b __i r Dislnbuﬂon. (if: .2 KL”... .- ...._____ ._..,. _... ._...__..w.. U\_MMMW‘ W» umwwﬁ Mrunforrandfor 2 SlandnnlNonmi = To read the t—table, we need df = n — 1 and the conﬁdence level. Then read the t-score as given be— low. . 1 J J 0 Select the column for the relevant conﬁdence level 0 Select the row for the relevant degree of freedom, df o Read the t-score “Find the t-score for a sample of size 7 and for a conﬁdence level 95%. df = n - 1 2 7 — 1 = 6, Conﬁdence level = 95%. Cents-inn Len! W_M_Liﬁ___§!__ 9’ 99‘ df {.qu {use 1925 in": ‘ms ‘mn I 3.078 6.3” ”.706 31.811 63.657 3|8.3 6 L440 L943 2.447 1H} 3.707 5.208 7 L435 I395 2.365 2.998 3.499 4.735 mmw»m as “*w‘¥m»wm“vmm Therefore. from the table. the corresponding t—score is 2.447. 5 ...
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