I am describing a trend in monthly Immunization totals to hospital
management. Immunizations are up 17% over last year's total at this time.
However, a simple linear trendline points downward because of seasonal work
patterns - very high in the beginning, then lower, then gradually bending
upward in the last several months. A moving average "trend" merely
approximates this year's work pattern - so, why display it at all? Yet, if I
were to choose to display a trendline, a moving average approximates the
actual peformance of this department. Is it useful to include a trendline in
this situation? (In a similar vein, I use a moving average to trend
physician's monthly peformance, but the overall reaction has been "so what?").

Douglas Eckert -

If you have enough data, one approach is to model the trend (long-run
average behavior) and seasonal components separately and then combine them
for forecasts. For an example workbook, see
http://www.mikemiddleton.com/LinearT...alForecast.xls

- Mike Middleton
http://www.DecisionToolworks.com
Decision Analysis Add-ins for Excel


"Douglas Eckert" wrote in message
...
I am describing a trend in monthly Immunization totals to hospital
management. Immunizations are up 17% over last year's total at this time.
However, a simple linear trendline points downward because of seasonal
work
patterns - very high in the beginning, then lower, then gradually bending
upward in the last several months. A moving average "trend" merely
approximates this year's work pattern - so, why display it at all? Yet,
if I
were to choose to display a trendline, a moving average approximates the
actual peformance of this department. Is it useful to include a trendline
in
this situation? (In a similar vein, I use a moving average to trend
physician's monthly peformance, but the overall reaction has been "so
what?").

Thanks a lot, Mike!

DOUG

"Mike Middleton" wrote:

Douglas Eckert -

If you have enough data, one approach is to model the trend (long-run
average behavior) and seasonal components separately and then combine them
for forecasts. For an example workbook, see
http://www.mikemiddleton.com/LinearT...alForecast.xls

- Mike Middleton
http://www.DecisionToolworks.com
Decision Analysis Add-ins for Excel


"Douglas Eckert" wrote in message
...
I am describing a trend in monthly Immunization totals to hospital
management. Immunizations are up 17% over last year's total at this time.
However, a simple linear trendline points downward because of seasonal
work
patterns - very high in the beginning, then lower, then gradually bending
upward in the last several months. A moving average "trend" merely
approximates this year's work pattern - so, why display it at all? Yet,
if I
were to choose to display a trendline, a moving average approximates the
actual peformance of this department. Is it useful to include a trendline
in
this situation? (In a similar vein, I use a moving average to trend
physician's monthly peformance, but the overall reaction has been "so
what?").