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Lecture by Professor Omar Hasan Kasule Sr. for Year 2 Semester 2 PPSD Session on Wednesday 21st March 2007
1.0 GRAPHIC LONGITUDINAL DATA SUMMARY
Time series analysis is a type of longitudinal data analysis that deals with time-bound events such as repeated measures in time. Such longitudinal data can be summarized graphically by using a time series plot of y against time.
Three types of patterns can be described: time trend, seasonal pattern, and random or irregular patterns, A pattern may be a mixture of more than one of those described above.
A scatter-plot of data against its immediate predecessor is another graphical way of identifying trends in time.
Moving averages may be used instead of raw scores to make the time series plot more stable.
Time series plots show trend and can be used for forecasting.
2.0 FORECASTING
Forecasts can be qualitative or quantitative. Quantitative forecasts use the time series graph for extrapolation.
3.0 CORRELATION AND REGRESSION MODELS
LONGITUDINAL REGRESSION MODELS
In a longitudinal regression model, time becomes the independent or ‘x’ variable. The regression equation is like the usual linear regression equation.
AUTOREREGRESSION
Auto-regression is when a regression model is used to relate a variable to its immediate predecessor. If they are related we know that there is a time trend.
AUTO-CORRELATION
Autocorrelation is correlation between a variable and its immediate predecessor. If there is correlation we know that there is a time trend.