@@ -116,8 +116,9 @@ By convention, we number the periods as 0 (Pretest), 1 (Intervention), 2
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(Cooldown), but other numbering is allowed provided that the order of the
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periods is unchanged.
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- This information is represented by the * ExperimentPeriods* object class.
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-
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+ This information is represented by the * ExperimentPeriods* object class. The
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+ start dates of each period must be specified, and finally end date of the
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+ experiment. This example has only a pretest period and one intervention period:
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``` {r message=TRUE, echo=FALSE}
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print(ExperimentPeriods(c("2015-01-05", "2015-02-16", "2015-03-15")))
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```
@@ -225,8 +226,9 @@ To plot the time series, use the plot method:
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plot(obj.gts)
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```
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- For more information of the method, type ` ?plot.GeoTimeseries `
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- at the R prompt.
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+ To hide the legend, add ` legend=FALSE ` . To plot the time series on log scale,
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+ add ` log.scale=TRUE ` . For more information of the method, type
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+ ` ?plot.GeoTimeseries ` at the R prompt.
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## Experiment Periods
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@@ -239,6 +241,10 @@ total).
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obj.per <- ExperimentPeriods(c("2015-01-05", "2015-02-16", "2015-03-15"))
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obj.per
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```
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+ To introduce a cooldown period, we would specify one more date.
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+
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+ To learn more about the function, type ` ?ExperimentPeriods ` at the R prompt.
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+
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## Geo Assignment
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@@ -307,6 +313,10 @@ represents the cost, along with the experiment periods and group numbers.
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result
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```
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+ Note that in this particular case, there is no ` cooldown.period ` , hence it is
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+ set to ` NULL ` . If there was one, we would specify the period number (for
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+ example, ` cooldown.period=2 ` ).
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+
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The resulting object (a * GBRROASAnalysisFit* object) contains the model fit:
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when printed, it shows its summary, which defaults to 90 percent credible
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intervals. To recalculate the interval with a different credibility level, we
@@ -413,16 +423,25 @@ bound and the point estimate). We refer to this confidence interval half-width
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by _ precision_ (which gets better as the confidence interval gets shorter).
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The function * DoROASPreanalysis* predicts the precision of the iROAS estimate
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- based on historical data provided. It simulates experiments with given period
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- lengths and records the precision from each simulated experiment. We can then
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- use the * summary* method to compute the precision given an ad spend change, or
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- find the ad spend change associated with a given precision.
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+ based on historical data provided. It simulates experiments (by resampling) with
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+ given period lengths and records the precision from each simulated
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+ experiment. We can then use the * summary* method to compute the precision given
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+ an ad spend change, or find the ad spend change associated with a given
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+ precision.
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+
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+ For each simulated geo experiment data set, ROAS and its precision is estimated.
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+ The process yields a distribution of the these estimates of precision. The
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+ summary method takes the empirical median as the point estimate. If the data
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+ set does not have strong seasonalities, the variation of this estimate should be
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+ fairly small.
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The process runs as follows:
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1 . Assign geos to treatment groups.
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1 . Run preanalysis to predict the precision.
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+
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+
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## A randomized geo assignment
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Randomized geo assignments can be done using `GeoStrata' objects. This object
@@ -501,8 +520,7 @@ assignment, the results are likely to be different.
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[ Measuring Ad Effectiveness Using Geo Experiments] ( http://static.googleusercontent.com/media/research.google.com/en//pubs/archive/38355.pdf )
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[ 3] Kerman, J. and Wang, P., and Vaver, J. (2017)
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- Estimating Ad Effectiveness using Geo Experiments in a
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- Time-Based Regression Framework.
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+ [ Estimating Ad Effectiveness using Geo Experiments in a Time-Based Regression Framework] ( https://research.google.com/pubs/pub45950.html )
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# Disclaimer
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This software is not an official Google product. For research purposes only. Copyright 2017 Google, Inc.
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