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Sesi Anova Kemometri
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PengantarUji t (2 asumsi)
1 sampel 2 meanPaired t-test
banyak sampel, 2 meanANOVA
1 sampel, beberapa perlakuan, beberapa mean
ANOVAAnalysis of variance (ANOVA) is a method
for testing the hypothesis that there is no difference between two or more population means (usually at least three)
Often used for testing the hypothesis that there is no difference between a number of treatments
AnovaOne-way ANOVA
Ada satu faktor yang mempengaruhi pengukuran (faktor random saja atau faktor terkendali saja) + random pada pengukuran dengan instrumen
When there is only one qualitative variable which denotes the groups and only one measurement variable (quantitative)
Two-way ANOVATerdapat dua atau lebih faktor, bahkan mungkin
terdapat interaksi keduanya yang mempengaruhi penghukuran + random pada pengukuran dengan instrumen
Kondisi ANOVA (beberapa mean)1 mean berbeda signifikan dengan semua meanSeluruh mean berbeda signifikan dengan tiap-tiap mean
Cara uji: Susun mean-mean dalam urutan dari kecilBandingkan mean-mean yang berdekatan
Uji:s(2/n) x th(n-1)
dengan s adalah within sample estimate σ0
Harga hitungan ini digunakan untuk menilai perbedaan-perbedaan mean
Uji Lanjutan: Least Significant Different
Pembandingan Beberapa MeanPerhatikan contoh: Pengujian stabilitas reagen fluoresensi peda berbagai kondisi penyimpanan (n = 3; h = 4)
Kondisi Replikasi pengukuran (n)
Mean
A Larutan fresh 102 100 101 101B Penyimpanan
gelap101 101 104 102
C Penyimpanan redup
97 95 99 97
D Penyimpanan terang
90 92 94 92
Overall mean 98
Amati, harga mean-mean berbeda (secara nominal)
Untuk data di atas, ANOVA akan menguji apakah perbedaan mean antarsampel terlalu besar untuk dianggap sebagai random error.
Hipotesis, H0 : harga mean tiap sampel tidak berbeda
Derajat Kebebasan:DK dalam sampel: 2 x 4 = 8 DK antarsampel : 3 (= 4 -1)
Pembandingan Beberapa Mean
PengujianHitung within-sample variationHitung between-sample variatonLakukan one-tiled F testJika F hitung > Ftabel , H0 ditolakJika diperlukan lakukan uji lanjutan, Least Significant Difference
Tinjauan Aritmatika
Source of Variation Sum of Squares Degree of freedom
Between-sample h – 1 = …..
Within –sample h(n - 1) = …..
Total hn - 1 = ……..
Table: Summary of sums and degree of freedom
Simplifying
Source of Variation Sum of Squares Degree of freedom
Between-sample h – 1 = …..
Within –sample by substraction by substraction
Total N - 1 = ……..
Table: Formula for one-way ANOVA calculation
Also, simplified by substracting an arbitrary number from each measurement
Two-way ANOVA
Treatment1 2 ... j ... c Row total
Block 1 x11 x12 ... x1j ... x1c T1
Block 2 X21 x22 ... x2j ... x2c T2
.... ... ... ... ... ... ... ...
.... ... ... ... ... ... ... ...Block i xi1 xi2 ... xij ... xic Ti
.... ... ... ... ... ... ... ...Block r xr1 xr2 ... xrj ... Xrc Tr
Column Total T.1 T.2 ... T.j ... T.C T = grand total
General form of table for two-way ANOVAof N measurements devided between c
treatment level and r bloks (N = cr)
Formulae for Two-Way ANOVASource of Variation Sum or Square Degree of
FreedomBetween treatment j T.2/r - T2/N c - 1
Between block iTi.2/r - T2/N r- 1
Residual By substraction By substraction
Total ij xij2/N - T2/N N - 1
ExampleIn an experiment to compare the percentage efficiency of diff. chelating agent in extracting metal ion from aquous solution the following results were obtained:
Chelating Agent
Day A B C D1 84 80 83 792 79 77 80 793 83 78 80 78
Controlled factor: chelating agent are choosen by the experimenter
Uncontrolled factor (random factor)
One-wayUntuk menguji
efek signifikan karena faktor terkontrol
Mengestimasi variansi faktor tak terkendali
Two-wayUntuk menguji
apakah beda agen pengkhelat menghasilkan beda efisiensi secara signifikan
Untuk menguji apakah day-to-day variation scr signifikan lebih besar dari pada variasi karena random error