Analisis Deret Waktu

Transkripsi

1 Analisis Deret Waktu Pertemuan 2 Cross section Jenis Data Beberapa pengamatan diamati bersama sama pada periode waktu tertentu Harga saham semua perusahaan yang tercatat di BEJ pada hari Rabu 27 Februari 2008 Time Series Satu pengamatan diamati selama sekian periode secara teratur Harga saham P.T. TELKOM di BEJ dari 2 Januari 2008 hingga 27 Februari 2008 Longitudinal/panel Beberapa pengamatan diamati bersama sama selama kurun waktu tertentu (gabungan cross section dan time series) Harga saham P.T. TELKOM, P.T. INDOSAT, dan P.T. Mobile8 di BEJ dari 2 Januari 2008 hingga 27 Februari

2 Pola Data Time Series Konstan Trend Seasonal Cyclic Metode Forecasting Metode forecasting dapat dibedakan menjadi dua kelompok: Smoothing Moving average, Single Exponential Smoothing, Double Exponential Smoothing, Metode Winter Modeling ARIMA, ARCH/GARCH 2

3 Year 2000?? Smoothing

4 Sekilas Tentang Smoothing Prinsip dasar: pengenalan pola data dengan menghaluskan hl variasi ilokal. l Prinsip penghalusan umumnya berupa ratarata. Beberapa metode penghalusan hanya cocok untuk pola data tertentu. Metode Yang Dibahas Single Moving Average Double Moving Average Single Exponential Smoothing Double Exponential Smoothing Metode Winter untuk musiman aditif Metode Winter untuk musiman multiplikatif 4

5 Ilustrasi All these methods will be illustrated with the following example: Suppose that a hospital would like to forecast the number of patients arrival from the following historical data: Patients Arrival Note: Although week 4 data is given, some methods require that forecast for period 4 is first computed before computing forecast for period 5. web4.uwindsor.ca/users/b/.../7.../lecture_5_forecasting_f04_1.ppt Time Series Methods Simple Moving Average ent arrivals Pati A moving average of order N is simply the arithmetic average of the most recent N observations. For -week moving averages N; for 6-week moving averages N6; etc. Actual patient arrivals

6 Time Series Methods Simple Moving Average ent arrivals Pati Patient Arrivals Given -week data, one-step-ahead forecast for week 4 or two-step-ahead forecast for week 5 is simply the arithmetic average of the first -week data Time Series Methods Simple Moving Average ent arrivals Pati Patient t Arrivals One -step - ahead forecast for week k4 70 F

7 Time Series Methods Simple Moving Average ent arrivals Pati Patient Arrivals Two -step - ahead forecast for week k5 F ent arrivals Pati Time Series Methods Simple Moving Average One-step-ahead forecast for week 5 is computed from the arithmetic average of weeks 2, and 4 data Patient t Arrivals One -step - ahead forecast for week k5 F

8 Time Series Methods Simple Moving Average 450 -week kma forecast 40 ent arrivals Pati Actual patient arrivals Time Series Methods Simple Moving Average 450 -week MA 6-week MA forecast forecast 40 ent arrivals Pati Actual patient arrivals

9 Single Moving Average Ide: data pada suatu periode dipengaruhi oleh data beberapa periode sebelumnya Cocok untuk pola data konstan/stasioner Prinsip dasar: Data smoothing pada periode ke t merupakan rata rata dari m buah data dari data periode ke t hingga ke (tm+1) t 1 S t m i t m + 1 Data smoothing pada periode ke t berperan sebagai nilai forecasting pada periode ke t+1 F t S t 1 dan F n,h S n X i 9

10 Ilustrasi MA dengan m Periode (t) Data (X t ) Smoothing (S t ) Forecasting (F t ) Pengaruh Pemilihan Nilai m Semula MA (m) MA (m6) Waktu MA dengan m yang lebih besar menghasilkan pola data yang lebih halus. 10

11 Example: ly Department Store Sales The weekly sales figures (in millions of dollars) presented din the following table are used by a major department store to determine the need for temporary sales personnel. Period (t) Sales (y) 1 5, 2 4,4 5,4 4 5,8 5 5,6 6 4,8 7 5,6 8 5,6 9 5,4 10 6,5 11 5,1 12 5, ,2 15 5,6 16 6,7 17 5,2 18 5,5 19 5,8 20 5,1 21 5,8 22 6,7 2 5, ,8 Example: ly Department Store Sales ly Sales Sales 4 Sales (y) s 11

12 Example: ly Department Store Sales Use a three-week moving average (k) for the department t store sales to forecast for the week 24 and 26. ( y + y22 + y The forecast error is ) yˆ 24 e 24 y 24 yˆ Example: ly Department Store Sales The forecast for the week 26 is ˆ 26 y y + y + y

13 Latihan: ly Department Store Sales Sales RMSE 0.6 ly Sales Forecasts s Sales (y) forecast Period (t) Sales (y) forecast faculty.wiu.edu/f-dehkordi/ds-5/.../moving-average-methods.ppt Double Moving Average Mirip dengan single moving average Cocok untuk data yang berpola tren Proses penghalusan dengan rata rata dilakukan dua kali t Tahap I: 1 S 1, t m i t m + 1 X i Tahap II: S t 1 2, t S1, i m i t m + 1 1

14 Double Moving Average (lanjutan) Forecasting dilakukan dengan formula dengan F2, tt, + h At + Bt( h) A 2S S t 1, t 2, t 2 B S S m 1 ( 1, 2, ) t t t Ilustrasi DMA dengan m t X t S 1,t S 2,t A t B t F 2,t

15 Pemilihan Model (lanjutan) Semula MA(m) MA(m6) SES(0.) SES(0.4) Waktu 15