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20.5: Time series

  • Page ID
    45278
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    Introduction

    Time series refer to any measure recorded over time. Stationary time series do not have trends or seasonality, just random (white) noise; differencing time series do have trends and or seasonality. Stationary time series will not have predictable patterns over the long term.

    This page is under construction. Examples and questions are in place, but not much else; here’s a resource on time series:

    http://www.itl.nist.gov/div898/handbook/pmc/section4/pmc4.htm

    R code

    To conduct time series analysis use built in functions like ts() and decompose(). HoltWinters() also useful, now part of stats. Lots of specialized time series packages with advanced features, including forecast, timeSeries (Financial time series), season (Seasonal analysis of health data), and many others.

    Note:

    Note 1: Caution — newer versions of R have HoltWinters() and related functions included with base package stats.

    Note 2: Rcmdr package for time series was RcmdrPlugin.epack , no longer available as of 2018.

    For up-to-date listing of time series packages, see https://cran.r-project.org/web/views/TimeSeries.html

    Time series data sets included in R and Rcmdr

    R Code:

    data(co2, package="datasets")
    co2 <- as.data.frame(co2)
    #convert to time series data type with ts()
    tCO2 <- ts(co2,frequency=12,start=c(1959),end=c(1997))
    plot.ts(tCO2)
    Plot of carbon dioxide levels at Mauna Loa over time, from years 1959 to 1997.
    Figure \(\PageIndex{1}\): CO2 data set from package datasets, comes with Rcmdr installation.

    Other datasets included with R

    carData::Arrests

    carData::Bfox

    carData::CanPop

    Note: Dr D needs to complete this list

    Example

    Get up-to-date CO2 data from NOAA as text file. Download to your computer, load and clean in your favorite spreadsheet app. Months came as numbers 1,2,3, etc., I changed to text, Jan, Feb, Mar, etc. I grabbed three columns: year, month, ppm for import to R.

    head(maunaLoa)

    R output:

    > head(maunaLoa)
      year month  ppm
    1 1958 Mar 315.70
    2 1958 Apr 317.45
    3 1958 May 317.51
    4 1958 Jun 317.24
    5 1958 Jul 315.86
    6 1958 Aug 314.93

    However, it turns out the time series functions are easiest to work if only the ppm data are included.

    tCO2 <- ts(maunaLoa[,"ppm"],frequency=12,start=c(1958,3),end=c(2020,10))
    head(tCO2)

    R output:

    > head(tCO2)
            Mar    Apr    May    Jun    Jul    Aug
    1958 315.70 317.45 317.51 317.24 315.86 314.93

    Get our plot (Figure \(\PageIndex{2}\)).

    plot(tCO2)
    Plot of carbon dioxide levels at Mauna Loa over time, from 1959 to October 2020.
    Figure \(\PageIndex{2}\): CO2 ppm monthly average data from NOAA, last data October 2020.

    Seasonal time series come with a trend component, a seasonal component, and a random component.

    R code:

    dectCO2 <- decompose(tCO2)
    head(dectCO2)
    plot(dectCO2)
    Decomposition of the 1959-2020 CO2 time series into its additive components: a general upward trending series over the years, a periodic sine-wave-like seasonal series, and a random series that varies over years and seasons.
    Figure \(\PageIndex{3}\): Observed (panel, top), trends over time (panel, second from top), seasonal changes (panel, second from bottom), and random error (panel, bottom).

    Forecasting

    Excellent resource at https://otexts.com/fpp2/

    Exponential smoothing, weighted averages of past observations, weighted so that more recent observations are more influential.

    Holt-Winters method extracts seasonal component (additive or multiplicative).

    #set start value to value of first observation
    tCO2cast <- HoltWinters(tCO2, l.start=315.42)
    #Predict for next ten years. Because frequency in ts() was monthly, ten years is h=120
    forecastCO2 <- forecast(tCO2cast, h=120)
    plot(forecastCO2, fcol="red")
    Plot of observed CO2 levels from 1959 to 2020, shown in black. Holt-Winters prediction of CO2 levels for the following 10 years, shown in red.
    Figure \(\PageIndex{4}\): Data in black, predicted values in red (additive) shaded by confidence interval.

    ARIMA models

    DrD needs to complete


    Questions

    1. If a time series data set obtains observations collected at yearly intervals, what value should you enter in ts() function for frequency?
    2. For the CO2 dataset included in Rcmdr (co2, datasets), obtain forecast for year 2020 and compare against actual 2020 data (see Figure \(\PageIndex{2}\)).
    3. Positive clinical samples between September 2015 and November 2020 for flu virus in the USA are provided in the data set below (scroll or click here). The frequency of observations was weekly. Apply decompose() and obtain the seasonal and trend components of the data set. Which month does the peak positive sample occur?
    4. Total pounds of fish (variable = Pounds) and pounds of Akule and Opelu (variable = Akule.Opelu) caught by commercial industry in Hawaii, from 2000 to 2018 are provided in the data set below (scroll or click here). Apply decompose() and obtain the seasonal and trend components of the data set for Total pounds and again for Akule (Selar crumenophthalmus) and Opelu (Decapterus macarellus). Is there evidence for trends, and if so, describe the trend. Is there evidence of seasonality? If so, which month did peak fishing occur?

    Flu data set this page

    Flu, extracted 28 Nov 2020 from https://gis.cdc.gov/grasp/fluview/fluportaldashboard.html

    Year Date Week Positive
    2015 09/28/15 40 1.05578
    2015 10/05/15 41 1.29662
    2015 10/12/15 42 1.10855
    2015 10/19/15 43 1.10807
    2015 10/26/15 44 1.12344
    2015 11/02/15 45 1.38224
    2015 11/09/15 46 1.19344
    2015 11/16/15 47 1.38506
    2015 11/23/15 48 1.39498
    2015 11/30/15 49 1.47544
    2015 12/07/15 50 2.51181
    2015 12/14/15 51 2.287
    2015 12/21/15 52 2.45958
    2016 01/04/16 1 2.93137
    2016 01/11/16 2 4.25384
    2016 01/18/16 3 5.48463
    2016 01/25/16 4 6.95974
    2016 02/01/16 5 9.69858
    2016 02/08/16 6 12.5491
    2016 02/15/16 7 15.5359
    2016 02/22/16 8 18.3621
    2016 02/29/16 9 21.1098
    2016 03/07/16 10 23.6454
    2016 03/14/16 11 19.972
    2016 03/21/16 12 18.4709
    2016 03/28/16 13 16.2265
    2016 04/04/16 14 14.0164
    2016 04/11/16 15 13.2362
    2016 04/18/16 16 12.3464
    2016 04/25/16 17 10.2615
    2016 05/02/16 18 8.12094
    2016 05/09/16 19 6.68559
    2016 05/16/16 20 5.81108
    2016 05/23/16 21 4.71918
    2016 05/30/16 22 3.0595
    2016 06/06/16 23 3.02006
    2016 06/13/16 24 1.82927
    2016 06/20/16 25 1.71228
    2016 06/27/16 26 1.22261
    2016 07/04/16 27 0.903312
    2016 07/11/16 28 0.869153
    2016 07/18/16 29 0.849185
    2016 07/25/16 30 0.781793
    2016 08/01/16 31 0.933921
    2016 08/08/16 32 0.900745
    2016 08/15/16 33 0.803482
    2016 08/22/16 34 1.40485
    2016 08/29/16 35 1.67771
    2016 09/05/16 36 1.46146
    2016 09/12/16 37 1.51255
    2016 09/19/16 38 1.74135
    2016 09/26/16 39 1.78369
    2016 10/03/16 40 1.56951
    2016 10/10/16 41 1.35914
    2016 10/17/16 42 1.40304
    2016 10/24/16 43 1.50862
    2016 10/31/16 44 1.91569
    2016 11/07/16 45 2.20089
    2016 11/14/16 46 2.57608
    2016 11/21/16 47 3.34773
    2016 11/28/16 48 3.3191
    2016 12/05/16 49 4.25987
    2016 12/12/16 50 6.68342
    2016 12/19/16 51 10.7819
    2016 12/26/16 52 13.9993
    2017 01/02/17 1 13.3436
    2017 01/09/17 2 15.373
    2017 01/16/17 3 18.2865
    2017 01/23/17 4 18.5299
    2017 01/30/17 5 21.4215
    2017 02/06/17 6 24.1525
    2017 02/13/17 7 24.5117
    2017 02/20/17 8 24.7251
    2017 02/27/17 9 19.772
    2017 03/06/17 10 19.2714
    2017 03/13/17 11 19.0338
    2017 03/20/17 12 19.7113
    2017 03/27/17 13 18.4816
    2017 04/03/17 14 15.4251
    2017 04/10/17 15 12.7395
    2017 04/17/17 16 9.69626
    2017 04/24/17 17 6.76776
    2017 05/01/17 18 5.91752
    2017 05/08/17 19 5.33264
    2017 05/15/17 20 4.86286
    2017 05/22/17 21 4.35223
    2017 05/29/17 22 4.16524
    2017 06/05/17 23 3.38586
    2017 06/12/17 24 3.06229
    2017 06/19/17 25 2.64932
    2017 06/26/17 26 2.53401
    2017 07/03/17 27 2.17791
    2017 07/10/17 28 2.16392
    2017 07/17/17 29 1.83895
    2017 07/24/17 30 1.80607
    2017 07/31/17 31 1.94796
    2017 08/07/17 32 1.90048
    2017 08/14/17 33 1.34281
    2017 08/21/17 34 1.43382
    2017 08/28/17 35 1.93535
    2017 09/04/17 36 1.88806
    2017 09/11/17 37 1.89622
    2017 09/18/17 38 1.66942
    2017 09/25/17 39 1.70313
    2017 10/02/17 40 2.20191
    2017 10/09/17 41 2.08975
    2017 10/16/17 42 2.17647
    2017 10/23/17 43 2.58279
    2017 10/30/17 44 3.60729
    2017 11/06/17 45 4.24472
    2017 11/13/17 46 5.29966
    2017 11/20/17 47 7.0877
    2017 11/27/17 48 7.30533
    2017 12/04/17 49 10.7453
    2017 12/11/17 50 15.3549
    2017 12/18/17 51 22.777
    2017 12/25/17 52 25.3864
    2018 01/01/18 1 25.3653
    2018 01/08/18 2 26.9421
    2018 01/15/18 3 27.034
    2018 01/22/18 4 27.3698
    2018 01/29/18 5 27.0643
    2018 02/05/18 6 26.9981
    2018 02/12/18 7 26.1174
    2018 02/19/18 8 22.6155
    2018 02/26/18 9 18.4867
    2018 03/05/18 10 15.6938
    2018 03/12/18 11 15.5813
    2018 03/19/18 12 15.328
    2018 03/26/18 13 15.1135
    2018 04/02/18 14 12.6888
    2018 04/09/18 15 11.2486
    2018 04/16/18 16 9.39813
    2018 04/23/18 17 7.99876
    2018 04/30/18 18 6.25914
    2018 05/07/18 19 4.39311
    2018 05/14/18 20 3.16606
    2018 05/21/18 21 2.39003
    2018 05/28/18 22 1.52934
    2018 06/04/18 23 1.57683
    2018 06/11/18 24 1.29914
    2018 06/18/18 25 1.02329
    2018 06/25/18 26 1.11356
    2018 07/02/18 27 1.00305
    2018 07/09/18 28 0.916118
    2018 07/16/18 29 1.0534
    2018 07/23/18 30 0.995099
    2018 07/30/18 31 0.953592
    2018 08/06/18 32 0.95729
    2018 08/13/18 33 0.764331
    2018 08/20/18 34 1.33625
    2018 08/27/18 35 1.50367
    2018 09/03/18 36 1.74739
    2018 09/10/18 37 1.68745
    2018 09/17/18 38 1.69929
    2018 09/24/18 39 1.49699
    2018 10/01/18 40 1.74855
    2018 10/08/18 41 1.6967
    2018 10/15/18 42 1.99298
    2018 10/22/18 43 2.05527
    2018 10/29/18 44 2.17372
    2018 11/05/18 45 2.7331
    2018 11/12/18 46 3.15674
    2018 11/19/18 47 3.92782
    2018 11/26/18 48 3.91485
    2018 12/03/18 49 6.23152
    2018 12/10/18 50 10.3644
    2018 12/17/18 51 14.2649
    2018 12/24/18 52 16.352
    2019 12/31/18 1 12.1387
    2019 01/07/19 2 12.7217
    2019 01/14/19 3 16.3174
    2019 01/21/19 4 19.3918
    2019 01/28/19 5 22.5493
    2019 02/04/19 6 25.1342
    2019 02/11/19 7 26.026
    2019 02/18/19 8 26.2407
    2019 02/25/19 9 26.0743
    2019 03/04/19 10 25.6065
    2019 03/11/19 11 26.1318
    2019 03/18/19 12 22.4805
    2019 03/25/19 13 19.3035
    2019 04/01/19 14 14.9422
    2019 04/08/19 15 11.9093
    2019 04/15/19 16 8.61102
    2019 04/22/19 17 5.84355
    2019 04/29/19 18 4.81976
    2019 05/06/19 19 3.83986
    2019 05/13/19 20 3.54159
    2019 05/20/19 21 3.41968
    2019 05/27/19 22 3.0826
    2019 06/03/19 23 2.78989
    2019 06/10/19 24 2.31579
    2019 06/17/19 25 1.90194
    2019 06/24/19 26 2.0806
    2019 07/01/19 27 2.42883
    2019 07/08/19 28 2.01653
    2019 07/15/19 29 2.21849
    2019 07/22/19 30 2.37706
    2019 07/29/19 31 2.39817
    2019 08/05/19 32 2.05446
    2019 08/12/19 33 2.08183
    2019 08/19/19 34 2.36167
    2019 08/26/19 35 3.45517
    2019 09/02/19 36 3.09749
    2019 09/09/19 37 2.48391
    2019 09/16/19 38 2.75656
    2019 09/23/19 39 2.74367
    2019 09/30/19 40 1.30976
    2019 10/07/19 41 1.47877
    2019 10/14/19 42 1.55203
    2019 10/21/19 43 2.25335
    2019 10/28/19 44 3.05701
    2019 11/04/19 45 5.16261
    2019 11/11/19 46 6.75594
    2019 11/18/19 47 9.54599
    2019 11/25/19 48 10.9385
    2019 12/02/19 49 11.6554
    2019 12/09/19 50 16.1542
    2019 12/16/19 51 22.533
    2019 12/23/19 52 26.9336
    2020 12/30/19 1 23.4883
    2020 01/06/20 2 23.1187
    2020 01/13/20 3 26.0826
    2020 01/20/20 4 28.2813
    2020 01/27/20 5 30.1465
    2020 02/03/20 6 30.2596
    2020 02/10/20 7 29.675
    2020 02/17/20 8 28.3215
    2020 02/24/20 9 25.7517
    2020 03/02/20 10 22.4914
    2020 03/09/20 11 15.8125
    2020 03/16/20 12 7.50171
    2020 03/23/20 13 2.32158
    2020 03/30/20 14 1.0312
    2020 04/06/20 15 0.61823
    2020 04/13/20 16 0.623139
    2020 04/20/20 17 0.218375
    2020 04/27/20 18 0.262953
    2020 05/04/20 19 0.326173
    2020 05/11/20 20 0.305966
    2020 05/18/20 21 0.212681
    2020 05/25/20 22 0.16518
    2020 06/01/20 23 0.339751
    2020 06/08/20 24 0.279818
    2020 06/15/20 25 0.38117
    2020 06/22/20 26 0.282336
    2020 06/29/20 27 0.210322
    2020 07/06/20 28 0.176197
    2020 07/13/20 29 0.37594
    2020 07/20/20 30 0.150451
    2020 07/27/20 31 0.132626
    2020 08/03/20 32 0.176141
    2020 08/10/20 33 0.132385
    2020 08/17/20 34 0.226904
    2020 08/24/20 35 0.314861
    2020 08/31/20 36 0.201675
    2020 09/07/20 37 0.186246
    2020 09/14/20 38 0.39985
    2020 09/21/20 39 0.224669
    2020 09/28/20 40 0.330089
    2020 10/05/20 41 0.400802
    2020 10/12/20 42 0.350483
    2020 10/19/20 43 0.25138
    2020 10/26/20 44 0.201148
    2020 11/02/20 45 0.176706
    2020 11/09/20 46 0.221837

    Fish data set in this page

    Fish, Hawaii state DLNR, Pounds refers to total catch, Akule.Opelu refers to pounds for the two kinds of fish

    Year Month Pounds Akule.Opelu
    1999 Jan 2064023 85331
    1999 Feb 2286785 89537
    1999 Mar 2083789 112897
    1999 Apr 2446840 136301
    1999 May 2300842 103692
    1999 Jun 2340116 134432
    1999 Jul 2646429 138814
    1999 Aug 2254408 96569
    1999 Sep 1926381 56598
    1999 Oct 2233789 76834
    1999 Nov 1730672 134706
    1999 Dec 1762375 92255
    2000 Jan 1501164 147104
    2000 Feb 1993373 104165
    2000 Mar 2220831 132028
    2000 Apr 2398180 119224
    2000 May 2557229 121268
    2000 Jun 2510298 145200
    2000 Jul 2270954 93883
    2000 Aug 1912654 69107
    2000 Sep 1365264 65007
    2000 Oct 1615117 51208
    2000 Nov 1388453 117493
    2000 Dec 1802926 121486
    2001 Jan 1481810 170702
    2001 Feb 1496356 44575
    2001 Mar 1579528 101764
    2001 Apr 1184591 89388
    2001 May 2091424 124193
    2001 Jun 1966886 61122
    2001 Jul 2113931 73266
    2001 Aug 1926661 29386
    2001 Sep 1353429 30268
    2001 Oct 1338289 29577
    2001 Nov 1747198 80350
    2001 Dec 1458336 22817
    2002 Jan 1517609 107406
    2002 Feb 1729084 31030
    2002 Mar 1747985 67691
    2002 Apr 2109451 101043
    2002 May 2069921 57251
    2002 Jun 1640151 100501
    2002 Jul 1979382 87584
    2002 Aug 1831678 65566
    2002 Sep 1734201 53162
    2002 Oct 1779207 93867
    2002 Nov 2191825 106167
    2002 Dec 2576191 67881
    2003 Jan 1910500 49420
    2003 Feb 2075168 55006
    2003 Mar 2245753 71616
    2003 Apr 1562751 102993
    2003 May 2440228 106600
    2003 Jun 1842907 101715
    2003 Jul 1957279 48453
    2003 Aug 2143823 69130
    2003 Sep 1503212 74525
    2003 Oct 1611779 70949
    2003 Nov 1668167 54004
    2003 Dec 2312537 43054
    2004 Jan 1605595 75751
    2004 Feb 1705533 94864
    2004 Mar 2079402 120305
    2004 Apr 1883704 90950
    2004 May 1830168 111599
    2004 Jun 1918622 76392
    2004 Jul 2029787 98937
    2004 Aug 1928009 72577
    2004 Sep 1620224 82650
    2004 Oct 1854643 74587
    2004 Nov 1981567 59753
    2004 Dec 2022272 44353
    2005 Jan 2088821 60972
    2005 Feb 2106948 59469
    2005 Mar 2386327 84551
    2005 Apr 2122171 101099
    2005 May 2369953 79042
    2005 Jun 2342117 104814
    2005 Jul 2281871 71065
    2005 Aug 2124303 53383
    2005 Sep 1734986 37195
    2005 Oct 1920131 48632
    2005 Nov 1969506 88235
    2005 Dec 2323933 98768
    2006 Jan 1702766 50553
    2006 Feb 2060204 89037
    2006 Mar 2244570 33916
    2006 Apr 2068922 74430
    2006 May 2164076 108689
    2006 Jun 1935951 89503
    2006 Jul 1968513 93758
    2006 Aug 1741802 111080
    2006 Sep 1508897 44537
    2006 Oct 1892535 46747
    2006 Nov 2208173 82938
    2006 Dec 1381412 42260
    2007 Jan 2211384 114496
    2007 Feb 2391437 60618
    2007 Mar 2724021 94251
    2007 Apr 2639245 90078
    2007 May 3168913 129258
    2007 Jun 2706972 116628
    2007 Jul 2523392 129345
    2007 Aug 2272502 88997
    2007 Sep 2121837 71560
    2007 Oct 2472996 52915
    2007 Nov 3040118 107555
    2007 Dec 2934174 39239
    2008 Jan 2656539 44672
    2008 Feb 3101819 35213
    2008 Mar 2816846 74421
    2008 Apr 3064837 63355
    2008 May 3560993 52287
    2008 Jun 2920219 33685
    2008 Jul 2516561 31288
    2008 Aug 2338205 62171
    2008 Sep 2314458 31311
    2008 Oct 2407240 42766
    2008 Nov 2060666 75102
    2008 Dec 2329268 74508
    2009 Jan 2198569 44459
    2009 Feb 2314764 33206
    2009 Mar 1846459 64879
    2009 Apr 2659230 36638
    2009 May 2692440 77011
    2009 Jun 2387175 49217
    2009 Jul 2672895 55033
    2009 Aug 2174027 40398
    2009 Sep 2259153 51386
    2009 Oct 2386749 58095
    2009 Nov 2081706 51798
    2009 Dec 2702871 55148
    2010 Jan 2059964 40855
    2010 Feb 2632985 100598
    2010 Mar 2430562 39887
    2010 Apr 2652013 40528
    2010 May 2460228 71483
    2010 Jun 2743053 120553
    2010 Jul 2278847 96315
    2010 Aug 2618427 62854
    2010 Sep 2483861 66613
    2010 Oct 2503321 53353
    2010 Nov 2370032 104360
    2010 Dec 2431047 57919
    2011 Jan 2527241 37755
    2011 Feb 2786453 51863
    2011 Mar 3789076 40188
    2011 Apr 3148826 60494
    2011 May 3015187 49037
    2011 Jun 2718583 58380
    2011 Jul 2284521 43096
    2011 Aug 2475519 33612
    2011 Sep 2461640 48697
    2011 Oct 2420554 49929
    2011 Nov 2059769 63045
    2011 Dec 2882776 64430
    2012 Jan 2825116 42894
    2012 Feb 2653892 23528
    2012 Mar 2544758 39839
    2012 Apr 3050109 47250
    2012 May 3264666 41357
    2012 Jun 2798204 56808
    2012 Jul 3331174 46853
    2012 Aug 2864088 62682
    2012 Sep 2219536 33641
    2012 Oct 2482162 47478
    2012 Nov 2545142 49232
    2012 Dec 3129507 35924
    2013 Jan 2902748 32373
    2013 Feb 2388197 21922
    2013 Mar 2831279 41718
    2013 Apr 2467444 54619
    2013 May 3131153 57183
    2013 Jun 2819983 33484
    2013 Jul 3473180 44240
    2013 Aug 2586863 52288
    2013 Sep 2459258 38145
    2013 Oct 3228317 48533
    2013 Nov 2998732 53187
    2013 Dec 3023918 33381
    2014 Jan 2503733 31233
    2014 Feb 2615184 33134
    2014 Mar 2808639 38876
    2014 Apr 2857514 45819
    2014 May 3363746 58283
    2014 Jun 2778689 54266
    2014 Jul 2828847 41221
    2014 Aug 3074061 39744
    2014 Sep 2703440 40668
    2014 Oct 2744813 37263
    2014 Nov 2541143 72020
    2014 Dec 3325799 44128
    2015 Jan 3130822 54942
    2015 Feb 2806020 45098
    2015 Mar 3560866 53378
    2015 Apr 3341695 43642
    2015 May 3717487 70583
    2015 Jun 3678283 56578
    2015 Jul 3954460 53615
    2015 Aug 3016100 42015
    2015 Sep 2209724 38904
    2015 Oct 2795409 55583
    2015 Nov 3426753 70399
    2015 Dec 3357454 51095
    2016 Jan 3087231 54089
    2016 Feb 3374485 48683
    2016 Mar 3260054 45472
    2016 Apr 2930106 63926
    2016 May 3383331 76757
    2016 Jun 3209613 45557
    2016 Jul 2765143 37198
    2016 Aug 2732867 40213
    2016 Sep 2180347 41660
    2016 Oct 2298348 34699
    2016 Nov 2545574 71924
    2016 Dec 3691485 37448
    2017 Jan 3383297 48974
    2017 Feb 2856584 35716
    2017 Mar 3413039 39789
    2017 Apr 3361156 30625
    2017 May 3576410 31092
    2017 Jun 3348469 27734
    2017 Jul 2741187 27041
    2017 Aug 2675625 32476
    2017 Sep 2700675 33394
    2017 Oct 2779159 31373
    2017 Nov 2817012 40681
    2017 Dec 3726216 33955
    2018 Jan 3361591 46166
    2018 Feb 2625263 29890
    2018 Mar 3219102 31454
    2018 Apr 3593287 25954
    2018 May 3798285 35908
    2018 Jun 3362829 31899
    2018 Jul 2735326 30968
    2018 Aug 2397549 19849
    2018 Sep 2323735 29324
    2018 Oct 2472451 28927
    2018 Nov 2687466 40497
    2018 Dec 3236293 36603

    This page titled 20.5: Time series is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Michael R Dohm via source content that was edited to the style and standards of the LibreTexts platform.

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