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Basic Statistics for Paid Search Advertising
1. BASIC STATISTICS
for PAID SEARCH ADVERTISING
Katharine Mission-Estenzo
SGS.com Search Engine Marketing Lead
Research & Testing Specialist and
Quality Management Coordinator
PPC Pinas Meetup 2013
May 31, 2013
Cypress Towers, Taguig
2. 2
OBJECTIVE & SCOPE
Introduce Statistical Concepts and Tools to efficiently
manage campaigns and results
Correct common misuses and misconceptions on Basic
Statistical concepts
Not a Statistics crash course - Guaranteed formula-free
presentation!
3. 3
TOPICS
Statistical Sampling and Analysis
Charts and Graphs
Common Numerical Misuses
Prediction and Forecasting
Statistical Process Control
5. 5
STATISTICAL SAMPLING?
Population
Target
Population
Samples
Selected
SAMPLING TECHNIQUES
Simple Random Sampling
Systematic Sampling
Stratified Sampling
Probability-proportional-to-size sampling
Accidental / Purposive Sampling
Quota Sampling
Clustered Sampling
SAMPLING PROCESS
Define the population of concern
Specify a sampling frame
Develop a sample plan
Implementing the sample plan
Sampling and data collecting
6. 6
WHY USE A SAMPLE?
• Lower Costs
• Faster Data CollectionResearch
• Validity of Results
• Robustness of
Statistical Model
• Statistical Significance
Testing
SAMPLINGERRORS
• History
• Instrumentation
• Selection
• Sampling
Distortion
7. 7
SIGNIFICANT VS STATISTICALLY SIGNIFICANT
SIGNIFICANT
Important
Essential
Meaningful
STATISTICALLY
SIGNIFICANT
Pattern
Behavior
Not by Chance
Before making conclusions, always make sure that you
have sufficient sample size. All test results are invalid if:
insufficient sample size
sampling errors
8. 8
SAMPLING ERROR = MARGIN OF ERROR
Sampling Error
• Failure to capture the profile of the true
population- under representation.
Margin of Error
• The difference of the estimated value to the true
population value
9. 9
GRAPH IT!
0
200
400
600
800
1000
1200
1400
1600
HACCP ISO 22000 GMP FSSC
22000
BRC
Page Visits
January 2013
0
200
400
600
800
1000
1200
1400
1600
1800
Jan February March April
Monthly Page Visits
Jan - Apr 2013
HACCP GMP FSSC 22000
HACCP
33%
ISO 22000
22%
GMP
18%
FSSC
22000
15%
BRC
12%
Page Visits
January 2013
Discrete/ count data –
Impressions, Clicks,
Conversions
Comparing data based on
a single category/ criteria
Change in magnitude/
quantity
Continuous data – CTR,
Conv Rate, CPC
Tracking changes over time
Trends
Correlations
Portions/ percentages of a
whole – Geo performances
One variable at a time
Limit your data – use bar
charts for more than six
variables
Avoid using 3D rotation -
deceiving
10. 10
COMBINATION GRAPHS
$0.00
$1.00
$2.00
$3.00
$4.00
$5.00
$6.00
0
10
20
30
40
50
60
Madrid Valencia Mallorca Zaragosa Tenerife
Conversions vs CPA
33.39% 31.90% 27.38% 27.16%
22.26% 24.07% 28.33% 28.86%
17.47% 19.06% 18.79% 16.98%
14.47% 13.14% 11.33% 11.88%
12.42% 11.84% 14.16% 15.11%
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
90.00%
100.00%
Jan February March April
Monthly Search Traffic Share
HACCP ISO 22000 GMP FSSC 22000 BRC
Clicks
Impressions
0
5000
10000
15000
20000
25000
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When using combination graphs (or
even simple graphs), keep in mind that
your objective is to simplify data
presentation. Present trends and changes
in the simplest form.
Do not complicate your graphs just to
give the impression of “advanced” analysis
and/or analytical skills.
11. 11
LIES, DAMNED LIES AND STATISTICS
The Danger of Averages
Bill Gates walk into a bar; on average, everybody in the bar is a
millionaire.
The average human has one breast and one testicle. ~Des McHale
The interesting thing about averages is that they hide the truth very
effectively. ~Avinash Kaushik
12. 12
MEASURES OF CENTRAL TENDENCY
Day
Earning
(USD)
Day 1 350.00
Day 2 400.00
Day 3 400.00
Day 4 5,500.00
Day 5 150.00
Day 6 300.00
Day 7 400.00
Day 8 400.00
Day 9 400.00
Day 10 400.00
Total 8,700.00
ON IMPULSE:
My average daily
earning is USD 870.00.
MEAN
Average
Minimal differences
Widely dispersed
data
Extremes and
outliers
MEDIAN
Middle value
Most resistant to
outliers and extreme
values
If data points are
even, this is the mean of
the 2 middle values
MODE
Most often appears
Most likely to be sampled
Not unique – data set may be mutli-modal
13. 13
Percentage Fallacies and Misuses
Using pure percentage values to measure effectiveness
CTR
Conversion Rates
Averaging Percentages – valid or not?
Trials Successes %
10 6 60.00%
25 10 40.00%
30 10 33.33%
40 5 12.50%
Totals 105 31 145.83%
AVERAGE = 36.46 %
AVERAGE = 29.52 %
14. 14
The Excuse of Trends and Seasonality
TREND - General tendency of a series of data points to move in a
certain direction over time
Consecutive data points moving in a single direction
Majority of data points moving in a single direction
Extreme values, singular peak values and outliers (Noise) are flattened in trend analysis
SEASONALITY – Characteristic of a time series in which the data
has regular and predictable changes on a specific period recurring
every calendar year
Always check previous data for the same time period
Not all holidays are causal to seasonality
15. 15
PREDICTION AND FORECASTING
TIME SERIES
A sequence of data points measured successively in uniform time
intervals
Use of a statistical model to predict future values based on previous
observations
! Assuming that conditions stay the same.
REGRESSION ANALYSIS
A technique for estimating the relationships between variables
The value of a dependent variable is affected by the behavior of the
values of the independent variables
! Check data for conformance to statistical assumptions.
16. 16
STATISTICAL PROCESS CONTROL
FMEA – Failure Mode and Effects Analysis
Identifying potential mistakes before they happen to determine whether the
effects are tolerable or not
FME(C)A – includes criticality analysis
Efficient assessment of
best option
Evaluate effects of
proposed changes on
processes & performances
Manage risks associated
with system failures and
changes
Standardize procedures
and practices
17. 17
Design
Measure
Analyze
Improve
Control
DMAIC – Six Sigma Core Concept
Campaign Objectives
Nature of Business
Advertising Channels
Type of Testing
Gap analysis/ Benchmark
Historical Data
Data Collection/ Testing
Identify sources of variation
Identify critical factors
Validation of results
Discover process
relationships
Implement optimization/
improvements
FMEA
Documentation
Develop Control Plan
Monitoring
18. 18
REMINDERS
TEST! Don’t rely on assumptions.
Efficiency – cost, time, energy
Always define objectives and targets clearly
Plan carefully – ensure objectives are met
Understand your data – how, where, what and when
Statistics – Bane or Boon?
For PPC, more often we use ymmetrical samplingWe divide samples equally among control and test conditions. Ensure ads are rotated evenly for split testingSampling plan includes parameters to be measured, range of values, sampling technique, sample size
Sampling Error – failure of the subset (sample) to represent/ capture the characteristics of the population of interestHistory – related to time – trendsInstrumentation – tools – tracking toolsSelection – subjects not evenly distributedSampling Distortion – failure to collect sufficient sample size
A significant change in conversions may not be statistically significant. It means that change may be due chances and/or such behavior may not last longStat sig – p value refers to probability that a given value will occur by chanceStat sig – when you repeat the test in the future given the same circumstances, results will be more or less the sameMec toolThe more samples, the more accurate results you getKey importance of sampling – Representativeness-in PPC sampling is important to help manage numerous campaigns, avoid making decisions based on small changes that may be due to chances. To make optimization efforts maximize their effectiveness
When you commit sampling errors, margin of error becomes greaterThe more samples, the lower the margin of error becomes
Correlations – use to indicate relationship variablesHowever, correlation does not imply causationThere may be additional factors to fully explain and measure the relationships of variables
1st graph– easily see what are needs attention: low conversions, higher CPA2nd graph – good for comparing share percentages month by month. However, changes in magnitude for monthly search traffic is not captured. Ex. Jan has 300 visits (100%) and February may have 200 (100%)3rd graph – area charts good if proportion is high- maybe 30% at least
The event of having an extreme value could distort the average valueSample: Average monthly conversion for 1 year, campaign may have consistent values ranging from 3ly 0-40 but for a month you peaked conversion at 150- average monthly conversions may be greater than the true “usual” monthly values
How to get the median- arrange data from highest to lowest and get the middle valueMedian 50% falls below and 50% falls aboveOutliers – peaks, extremely large value, very far from the usual valuesIn PPC – using average position is not that advisableAve CPC – check daily for actual cpc
Percentages depend on their base population – it is a measure of proportion-CTR for keywords – consider search volumes-conversion rates – compare with the ad serving share (more fair % because this is portion of the whole)Do not sum up % then divide by the data points. Always get total success divided by total # of trials
Advanced Trend and Seasonality analysis – Deseasonalizing – get seasonality index and divide each data point with itAt least 3 yearsNo data on trends or seasonality- deduction analysis of all campaign elements
Time series is not a simple sequence nor is it based on a single variable only- it is a statistical model considering all variables that may affect the variable of interestApplicationsTime Series – annual returns and gains, ROI’s, speech recognition, earthquake predictionsRegression – ex. finding out what affects CPCBe careful to use in PPC because, certain parameters may not have linear relationshipsStatistical tests have assumptions to fulfill before the results are considered statistically correct
FMEA is a design tool sample is the PPC Best Practices guide
You’ve been doing this
Review concepts before planning your testsKnow your data- how is it gathered, where it may come from, what is it for and when – concerns related to time