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Statistical Analysis Of Coal Production In Nigeria (1990-1999)
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TIME-SERIES ANALYSIS AND APPLICATIONS:
Montgomery
and Lynwood (1976) stated that “a time series is a sequence of
observations on a variable of interest. The variable is observed at
discrete time points usually equally spaced.
Mordi (1992) defined
“time series as an arraignment of statistical data ordered according to
the fines of its occurrence in data classified chronologically. “Thus a
collection of numerical values of a particular variable listed in
chronological order is known as time-series. The record of months scale
and production of a company over a number of months or years, the
schools daily attendance, amount of annual rainfall over a number of
years, the weights of an animal record at different stages of growth are
all examples of time series. the time can be days, weeks, months,
years, decades or even seconds.
Ifeagwu (1992) states that “time
series involves classifying and studying, the patterns of movement of
the values of the variable over regular time. It enhances under standing
of the past and current pattern of changes. It provides dues about
future patterns which aid in forecasting and such information is needed
by researchers and policymakersâ€.
Spiegel (1972) and Nwabuokei (1986)
observed that the characteristic movements to time series may be
classified into four main types. Often caked components of a time
series.
Long term or secular movements: refers to the general
direction in which the graph of a time series appears to be going over
long interval of time.
Cyclical movements: refers to the long term
oscillations or swings about trend line or curve. These cycles, as they
are sometimes called May or may not be periodic is they may or may not
follow exactly similar patterns after equal internals for time. In
business and economic activity, movements are considered cyclical only
if they recur after time intervals of more than a year. An important
example of cyclical movement is the so called business cycles
representing intervals of prosperity recession, depression and
recovering.
Seasonal movement: refer to the identical or almost
identical pattern which a time series appear to follow during
corresponding months of successive years such movement are due to
recurring events which take place annually, as for instance the sudden
increase of departmental stores sales before Christmas.
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