**Contents**show

### 1. What is A/B Testing?

**Answer:**

A/B testing, also known as split testing, is an experimentation method used in marketing and product development. It involves comparing two versions of a webpage or app to determine which one performs better in terms of a specific goal.

### 2. How do you set up an A/B test?

**Answer:**

- Define the goal and hypothesis.
- Identify the control and variant groups.
- Implement tracking and analytics.
- Randomly assign users to groups.
- Run the test for a sufficient duration.
- Analyze the results using statistical methods.

### 3. Explain the concept of statistical significance in A/B Testing.

**Answer:**

Statistical significance ensures that the observed differences in conversion rates between variants are not due to chance. It is typically determined using hypothesis testing and p-values.

### 4. How do you calculate sample size for an A/B test?

**Answer:**

Use power analysis to calculate the sample size needed to detect a meaningful difference with a desired level of confidence and power. Online calculators or statistical software can help with this.

### 5. What is a control group in A/B Testing?

**Answer:**

The control group is exposed to the existing version (current state) of the webpage or app. It serves as the baseline against which the variant groupโs performance is compared.

### Code Snippet for Random Assignment:

```
import random
def assign_to_group():
if random.random() < 0.5:
return 'control'
else:
return 'variant'
```

### 6. How do you analyze the results of an A/B test?

**Answer:**

Use statistical techniques like t-tests or chi-squared tests to compare the performance metrics of the control and variant groups. Additionally, consider practical significance and potential biases.

### Code Snippet for T-Test (Python):

```
from scipy.stats import ttest_ind
def ab_test_results(control_group, variant_group):
t_stat, p_value = ttest_ind(control_group, variant_group)
return t_stat, p_value
```

### 7. What is a p-value in the context of A/B testing?

**Answer:**

The p-value represents the probability of observing the data if there is no real difference between the control and variant groups. A lower p-value indicates stronger evidence against the null hypothesis.

### 8. How do you handle multiple comparisons in A/B testing?

**Answer:**

Apply corrections like Bonferroni correction or use techniques like False Discovery Rate (FDR) control to account for the increased risk of Type I errors when conducting multiple tests.

### 9. What is the difference between A/A testing and A/B testing?

**Answer:**

A/A testing involves comparing identical versions (no difference) to check for consistency and validate the testing methodology. A/B testing compares different versions to determine which performs better.

### 10. What are some common pitfalls in A/B testing?

**Answer:**

Common pitfalls include insufficient sample size, biased sampling, running tests for insufficient durations, and misinterpreting results without considering practical significance.

### 11. How do you ensure the validity of an A/B test?

**Answer:**

Ensure randomization, control group isolation, and consistent user experience. Also, consider factors like external events and seasonality. Pre-test analysis and post-test checks are crucial for validity.

#### Code Snippet for Pre-Test Analysis (Python):

```
import pandas as pd
def pre_test_analysis(control_group, variant_group):
control_mean = control_group.mean()
variant_mean = variant_group.mean()
return control_mean, variant_mean
```

### 12. What is the difference between A/B testing and multivariate testing?

**Answer:**

A/B testing compares two versions of a webpage or app to determine the better performer. Multivariate testing examines multiple elements (e.g., headlines, images) to find the optimal combination.

### 13. What is a conversion rate in the context of A/B testing?

**Answer:**

The conversion rate is the percentage of users who complete a desired action (e.g., making a purchase) out of the total visitors to a webpage or app.

### 14. How do you deal with โpeekingโ or โstoppingโ in A/B testing?

**Answer:**

Avoid โpeekingโ by deciding in advance how long the test will run. Use sequential testing with methods like the Sequential Probability Ratio Test (SPRT) to periodically check results without risking Type I errors.

#### Code Snippet for SPRT (Python):

```
import numpy as np
def sequential_test(data, alpha=0.05, beta=0.1):
t = 0
while True:
t += 1
if t >= len(data):
return "Continue"
z = np.abs((data[t] - data[0]) / np.sqrt(data[0] * (1 - data[0]) / t)) # Calculate z-score
if z >= norm.ppf(1 - alpha/2) or z <= norm.ppf(beta/2):
return "Stop"
```

### 15. What is the role of cohort analysis in A/B testing?

**Answer:**

Cohort analysis groups users based on common characteristics (e.g., sign-up date) to analyze their behavior over time. It helps identify trends and patterns that can impact A/B test results.

### 16. How do you handle A/A tests that show significant differences?

**Answer:**

If significant differences arise in A/A tests, it could indicate issues with randomization or data collection. Investigate and address potential sources of bias before proceeding.

### 17. What is the impact of the โSimpsonโs Paradoxโ in A/B testing?

**Answer:**

Simpsonโs Paradox occurs when a trend appears in different groups of data but disappears or reverses when the groups are combined. It highlights the importance of considering subpopulations in analysis.

### 18. How do you account for seasonality in A/B testing?

**Answer:**

Account for seasonality by comparing data within the same season or by using techniques like time series decomposition to remove seasonal effects from the analysis.

#### Code Snippet for Time Series Decomposition (Python):

```
from statsmodels.tsa.seasonal import seasonal_decompose
def remove_seasonality(data):
result = seasonal_decompose(data, model='multiplicative')
deseasonalized_data = data / result.seasonal
return deseasonalized_data
```

### 19. Explain the concept of Bayesian A/B testing.

**Answer:**

Bayesian A/B testing uses Bayesian statistics to update prior beliefs about conversion rates with observed data. It provides a probability distribution of likely outcomes rather than a single point estimate.

### 20. How do you communicate A/B test results to stakeholders?

**Answer:**

Present results with clear visualizations, focusing on key performance indicators (KPIs) and statistical significance. Provide context, explain limitations, and offer actionable insights for decision-making.

### 21. What is the importance of segmentation in A/B testing?

**Answer:**

Segmentation involves analyzing the performance of different user groups separately. It helps in understanding how changes impact specific user demographics or behaviors, providing more nuanced insights.

### 22. How do you handle A/B tests with low traffic?

**Answer:**

For low traffic scenarios, consider extending the test duration to accumulate sufficient data. Alternatively, use techniques like bootstrapping or Bayesian methods to estimate results with limited data.

### Code Snippet for Bootstrapping (Python):

```
import numpy as np
def bootstrap(data, n_iterations=10000):
bootstrap_samples = [np.random.choice(data, size=len(data), replace=True) for _ in range(n_iterations)]
means = [sample.mean() for sample in bootstrap_samples]
return np.percentile(means, [2.5, 97.5])
```

### 23. What are some common types of biases in A/B testing?

**Answer:**

Selection bias, novelty effect, and time-of-day effects are common biases. Selection bias occurs when the sample is not representative. Novelty effect is the initial excitement about a change. Time-of-day effects result from variations in user behavior.

### 24. How do you account for the โwinnerโs curseโ in A/B testing?

**Answer:**

The winnerโs curse occurs when the observed effect size is an overestimate of the true effect. To account for it, consider conducting sensitivity analyses or applying Bayesian methods to estimate more realistic effect sizes.

### 25. What is the role of ethics in A/B testing?

**Answer:**

Ethics in A/B testing involves ensuring transparency, informed consent, and fairness to users. Avoid deceptive practices, prioritize user experience, and comply with privacy regulations.

### 26. How do you handle A/B tests with non-binary outcomes (e.g., revenue, engagement score)?

**Answer:**

For non-binary outcomes, use techniques like Bayesian methods or regression models to analyze continuous data. Consider using metrics like Average Revenue Per User (ARPU) or Customer Lifetime Value (CLV) for evaluation.

#### Code Snippet for Bayesian Regression (Python):

```
import pymc3 as pm
def bayesian_regression(control_data, variant_data):
with pm.Model() as model:
alpha = pm.Normal('alpha', mu=0, sd=10)
beta = pm.Normal('beta', mu=0, sd=10)
sigma = pm.HalfNormal('sigma', sd=10)
mu = alpha + beta * control_data
y = pm.Normal('y', mu=mu, sd=sigma, observed=variant_data)
trace = pm.sample(1000, tune=1000)
return trace
```

### 27. How do you handle โpost-experiment dippingโ in A/B testing?

**Answer:**

Post-experiment dipping refers to a temporary decrease in metrics immediately after a change. It can be caused by user adjustment. Allow for a stabilization period before drawing conclusions.

### 28. What is the role of randomization in A/B testing?

**Answer:**

Randomization ensures that participants are assigned to control and variant groups in a way that minimizes bias. It helps in making causal inferences about the impact of changes.

### 29. How do you deal with non-compliance or โcontaminationโ in A/B testing?

**Answer:**

Non-compliance occurs when users in one group experience the treatment meant for the other group. Monitor and analyze the extent of non-compliance, and consider sensitivity analyses to account for it.

### 30. What are the limitations of A/B testing?

**Answer:**

A/B testing cannot explain โwhyโ certain changes led to results. Itโs limited to the tested variables and may not capture long-term effects or complex interactions.

### 31. What is the difference between frequentist and Bayesian approaches in A/B testing?

**Answer:**

Frequentist approach relies on probabilities based on observed data and assumes fixed but unknown parameters. Bayesian approach incorporates prior beliefs and updates them with observed data to obtain a probability distribution.

### 32. How do you handle โcarryover effectsโ in A/B testing?

**Answer:**

Carryover effects occur when exposure to one treatment influences responses to subsequent treatments. Use techniques like counterbalancing, washout periods, or within-subject designs to minimize carryover effects.

### 33. What is โexternal validityโ in the context of A/B testing?

**Answer:**

External validity refers to the generalizability of A/B test results to a broader population or context. Itโs crucial to consider whether findings can be applied beyond the test environment.

### 34. How do you choose the appropriate significance level (alpha) for an A/B test?

**Answer:**

Select alpha based on the acceptable level of Type I error (false positive rate). Common choices include 0.05 or 0.01, but it should be determined based on the specific context and tolerance for false positives.

### 35. What is the role of a โnull hypothesisโ in A/B testing?

**Answer:**

The null hypothesis states that there is no significant difference between the control and variant groups. It serves as the baseline assumption to be tested against the alternative hypothesis.

### 36. How do you handle โregression to the meanโ in A/B testing?

**Answer:**

Regression to the mean occurs when extreme observations are followed by less extreme ones. To address this, use statistical controls or consider including a pre-test period in the analysis.

### 37. What is the impact of long-tailed distributions on A/B testing?

**Answer:**

Long-tailed distributions indicate that a small number of observations have high values. They may require different statistical methods, like non-parametric tests, to handle the skewed data.

### 38. How do you account for time zone differences in A/B testing?

**Answer:**

Consider running tests for a duration that spans different time zones or use techniques like time-based stratification to evenly distribute traffic across time periods.

### Code Snippet for Time-Based Stratification (Python):

```
def stratify_by_time(data, num_time_periods):
periods = np.linspace(0, len(data), num_time_periods+1, dtype=int)
groups = [data[periods[i]:periods[i+1]] for i in range(num_time_periods)]
return groups
```

### 39. What is โinteraction effectโ in A/B testing?

**Answer:**

An interaction effect occurs when the impact of one variable depends on the level of another variable. Itโs important to consider these interactions in A/B testing analysis.

### 40. How do you handle โuser learningโ in A/B testing?

**Answer:**

User learning effects occur when users become more proficient or accustomed to a change over time. Account for this by analyzing data over longer durations or by considering learning curves in the analysis.

### 41. How do you address โseasonalityโ in A/B testing?

**Answer:**

To account for seasonality, segment the data by time periods and compare performance within the same season. Alternatively, use time series analysis techniques like ARIMA or Exponential Smoothing.

#### Code Snippet for Seasonal Decomposition (Python):

```
from statsmodels.tsa.seasonal import seasonal_decompose
def seasonal_decomposition(data):
result = seasonal_decompose(data, model='additive', period=seasonality)
seasonal = result.seasonal
trend = result.trend
residual = result.resid
return seasonal, trend, residual
```

### 42. What is the purpose of a โpower analysisโ in A/B testing?

**Answer:**

A power analysis helps determine the sample size needed to detect a meaningful effect with a desired level of confidence. It ensures the test has sufficient statistical power to make valid conclusions.

### 43. How do you handle โmultiple comparisonsโ in A/B testing?

**Answer:**

To address multiple comparisons, apply corrections like Bonferroni, Holmโs method, or False Discovery Rate (FDR) control. These methods control the familywise error rate or false discovery rate.

### 44. What is โp-value hackingโ and how do you avoid it?

**Answer:**

P-value hacking is manipulating the experiment or analysis to achieve a desired result. Avoid it by pre-specifying the analysis plan, including the metrics of interest, before conducting the test.

### 45. How do you interpret a confidence interval in A/B testing?

**Answer:**

A confidence interval provides a range of values within which the true parameter is likely to fall. For example, a 95% confidence interval implies that we are 95% confident the true value lies within that range.

### 46. What is โeffect sizeโ in the context of A/B testing?

**Answer:**

Effect size quantifies the magnitude of the difference between the control and variant groups. It indicates the practical significance of the observed effect.

### 47. How do you deal with โSimpsonโs Paradoxโ in A/B testing?

**Answer:**

Simpsonโs Paradox occurs when a trend appears in different groups of data but disappears or reverses when these groups are combined. Address it by understanding the underlying causal relationships and considering subgroup analyses.

### 48. What is the โBonferroni correctionโ in A/B testing?

**Answer:**

The Bonferroni correction adjusts the significance level (alpha) to account for multiple comparisons. It divides the original alpha by the number of comparisons to maintain a controlled familywise error rate.

### 49. How do you validate the results of an A/B test?

**Answer:**

Validate results by conducting follow-up tests or experiments to confirm the initial findings. Additionally, perform cross-validation or conduct a similar test with a different experimental setup to confirm the robustness of the results.

### 50. What is the role of โcohortsโ in A/B testing?

**Answer:**

Cohorts involve grouping users based on shared characteristics or behaviors. They help analyze how different user groups respond to changes over time, providing deeper insights into user behavior.

### 51. How do you handle โoutliersโ in A/B testing data?

**Answer:**

Outliers can skew results. Consider identifying and removing extreme outliers or transforming the data using techniques like winsorizing or robust statistical methods.

### Code Snippet for Winsorizing (Python):

```
def winsorize(data, alpha=0.05):
lower_bound = np.percentile(data, 100*alpha/2)
upper_bound = np.percentile(data, 100*(1-alpha/2))
return np.clip(data, lower_bound, upper_bound)
```

### 52. What is the โhierarchical modelingโ approach in A/B testing?

**Answer:**

Hierarchical modeling accounts for dependencies or hierarchies in the data. It allows for modeling of higher-level group effects, such as different user segments, in addition to individual-level effects.

### 53. How do you handle โpre-existing trendsโ in A/B testing?

**Answer:**

Pre-existing trends refer to ongoing changes in user behavior prior to the experiment. Use techniques like interrupted time series analysis to differentiate the impact of the change from existing trends.

### Code Snippet for Interrupted Time Series Analysis (Python):

```
from statsmodels.tsa.seasonal import seasonal_decompose
def interrupted_time_series(data, intervention_point):
pre_intervention = data[:intervention_point]
post_intervention = data[intervention_point:]
# Analyze trends in both periods
# ...
```

### 54. What is โsequential testingโ in A/B testing?

**Answer:**

Sequential testing involves examining the results of an A/B test as the data accumulates, rather than waiting until a fixed sample size is reached. It allows for early stopping if significant results are observed.

### 55. How do you handle โsample pollutionโ in A/B testing?

**Answer:**

Sample pollution occurs when test participants are exposed to multiple variations. Mitigate this by implementing techniques like IP-based exclusion or using cookie-based methods to ensure users are consistently assigned to one variation.

### 56. What is โpost-stratificationโ in A/B testing?

**Answer:**

Post-stratification involves dividing the data into strata (subgroups) based on specific characteristics after the experiment has concluded. It helps analyze the impact of treatments on specific segments.

### 57. How do you account for โspillover effectsโ in A/B testing?

**Answer:**

Spillover effects occur when the treatment group indirectly influences the control group (or vice versa). Use techniques like geographic targeting or utilizing separate control groups to minimize spillover.

### 58. What is the โCUPEDโ method in A/B testing?

**Answer:**

Controlled, Unbiased, Pre-Experimental Difference (CUPED) is a technique to reduce bias by adjusting pre-experiment data to make it more similar to the experimental group, improving the accuracy of the comparison.

### 59. How do you handle โseasonal trendsโ in A/B testing?

**Answer:**

To address seasonal trends, perform seasonal adjustment or include seasonal indicators in the analysis. This helps isolate the impact of the treatment from the underlying seasonal patterns.

### Code Snippet for Seasonal Adjustment (Python):

```
from statsmodels.tsa.seasonal import seasonal_decompose
def seasonal_adjustment(data):
result = seasonal_decompose(data, model='multiplicative', period=seasonality)
seasonal = result.seasonal
adjusted_data = data / seasonal
return adjusted_data
```

### 60. What is โcovariate adjustmentโ in A/B testing?

**Answer:**

Covariate adjustment involves accounting for the influence of covariates (other variables) on the response variable. It helps control for confounding factors and improves the accuracy of the comparison between groups.

### 61. What is โBayesian A/B testingโ and how does it differ from traditional frequentist methods?

**Answer:**

Bayesian A/B testing uses Bayesian statistics to analyze experiment results. It provides a probability distribution for the treatment effect, allowing for direct probability statements about the hypothesis. This differs from frequentist methods, which rely on p-values and confidence intervals.

### 62. How do you address โselection biasโ in A/B testing?

**Answer:**

Selection bias occurs when the assignment of participants to groups is not random. Use techniques like randomization, stratification, or matching to ensure groups are comparable and minimize bias.

### 63. What is the โThompson Samplingโ algorithm in A/B testing?

**Answer:**

Thompson Sampling is a Bayesian method used in online decision-making, often applied in multi-armed bandit problems. It continually updates beliefs about the performance of different options and uses these beliefs to make decisions.

### Code Snippet for Thompson Sampling (Python):

```
import numpy as np
def thompson_sampling(alpha, beta):
samples = np.random.beta(alpha, beta)
choice = np.argmax(samples)
return choice
```

### 64. How do you handle โnon-binaryโ outcomes in A/B testing?

**Answer:**

For non-binary outcomes (e.g., continuous or count data), use appropriate statistical tests like t-tests, ANOVA, or regression models. Ensure the chosen method aligns with the nature of the data.

### 65. What is โSensitivity Analysisโ in the context of A/B testing?

**Answer:**

Sensitivity analysis involves testing the robustness of conclusions by varying assumptions or parameters. It helps assess how different scenarios or changes might affect the results and conclusions of an A/B test.

### 66. How do you deal with โlong-tailed distributionsโ in A/B testing?

**Answer:**

Long-tailed distributions may require specialized techniques like non-parametric tests or transformations. Consider bootstrapping or using robust statistical methods to handle outliers and skewed data.

### Code Snippet for Bootstrapping (Python):

```
def bootstrap(data, n_iterations=1000):
statistics = []
for _ in range(n_iterations):
sample = np.random.choice(data, size=len(data), replace=True)
statistic = np.mean(sample) # Or any desired metric
statistics.append(statistic)
return statistics
```

### 67. What is โcross-device testingโ and why is it important?

**Answer:**

Cross-device testing involves assessing how variations perform across different devices (e.g., desktop, mobile). Itโs crucial to ensure a consistent user experience across platforms.

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### 68. How do you address โcarryover effectsโ in A/B testing?

**Answer:**

Carryover effects occur when exposure to one variation influences the response to subsequent variations. Implement techniques like randomizing exposure sequences or incorporating a washout period to mitigate carryover effects.

**Answer:**

Bayesian Bandits is a sequential decision-making framework closely related to A/B testing. Itโs used in scenarios with multiple options and allows for continual learning and adaptation based on observed outcomes.

### 70. How do you handle โsmall sample sizesโ in A/B testing?

**Answer:**

With small sample sizes, consider techniques like bootstrapping or Bayesian methods which can provide more stable estimates. Additionally, focus on effect size and practical significance rather than relying solely on statistical significance.

### 71. What is the โBonferroni correctionโ and when is it used in A/B testing?

**Answer:**

The Bonferroni correction is a method to control the familywise error rate when conducting multiple comparisons. In A/B testing, itโs applied when analyzing multiple metrics or conducting multiple pairwise comparisons. It adjusts the significance level to account for the increased chance of Type I errors.

### 72. How do you handle โnon-normalityโ in A/B testing data?

**Answer:**

For non-normally distributed data, consider non-parametric tests like the Mann-Whitney U test or permutation tests. Alternatively, transformations or bootstrapping can be applied to approximate normality.

### 73. What is โrepeated measures designโ in A/B testing?

**Answer:**

Repeated measures design involves testing the same subjects under different conditions. Itโs useful when the same users are exposed to multiple variations, allowing for within-subject comparisons.

### 74. How do you account for โseasonalityโ in time-based experiments?

**Answer:**

To address seasonality, include seasonal indicators or use time series models to capture underlying patterns. This allows for a more accurate assessment of the treatmentโs impact.

### Code Snippet for Time Series Seasonal Decomposition (Python):

```
from statsmodels.tsa.seasonal import seasonal_decompose
def seasonal_decomposition(data, period):
result = seasonal_decompose(data, model='additive', period=period)
seasonal = result.seasonal
trend = result.trend
residual = result.resid
return seasonal, trend, residual
```

### 75. What is โblockingโ in experimental design and how does it apply to A/B testing?

**Answer:**

Blocking involves grouping participants based on specific characteristics before randomization. It helps control for potential confounding factors and ensures balance across treatment groups.

### 76. How do you handle โmissing dataโ in A/B testing?

**Answer:**

Address missing data by considering techniques like imputation or conducting sensitivity analyses to assess the potential impact of missing values on the results.

### 77. What is โsequential testingโ in the context of A/B testing?

**Answer:**

Sequential testing involves examining the results of an A/B test as data accumulates, rather than waiting until a fixed sample size is reached. It allows for early stopping if significant results are observed.

### 78. What is โcovariate adjustmentโ in A/B testing?

**Answer:**

Covariate adjustment involves incorporating additional variables (covariates) into the analysis to reduce noise and increase precision. It helps control for potential confounding factors and can lead to more accurate treatment effect estimates.

**Answer:**

For social platforms, consider techniques like network-based experiments or use methods that account for the interconnectedness of users. Graph-based models or propensity score matching with network features can be effective.

### 80. What is โpowerโ in the context of A/B testing?

**Answer:**

Power is the probability of detecting a true effect (i.e., rejecting the null hypothesis) when it exists. Itโs influenced by factors like sample size, effect size, and significance level. Higher power indicates a better chance of detecting real differences.

### 81. How do you handle โordinalโ or โcategoricalโ outcomes in A/B testing?

**Answer:**

For ordinal or categorical outcomes, apply techniques like ordinal regression or chi-squared tests. Ensure the chosen method aligns with the nature of the data and the research question.

### 82. What is โonline-to-offlineโ testing and when is it relevant?

**Answer:**

Online-to-offline testing involves assessing the impact of online interventions on offline behavior (e.g., online ad campaigns affecting in-store visits). Itโs relevant for businesses with both online and physical presences.

### 83. How do you address โcarryover effectsโ in A/B testing?

**Answer:**

Carryover effects occur when exposure to one variation influences the response to subsequent variations. Implement techniques like randomizing exposure sequences or incorporating a washout period to mitigate carryover effects.

**Answer:**

Bayesian Bandits is a sequential decision-making framework closely related to A/B testing. Itโs used in scenarios with multiple options and allows for continual learning and adaptation based on observed outcomes.

### 85. How do you handle โsmall sample sizesโ in A/B testing?

**Answer:**

With small sample sizes, consider techniques like bootstrapping or Bayesian methods which can provide more stable estimates. Additionally, focus on effect size and practical significance rather than relying solely on statistical significance.

### 86. What is the โBonferroni correctionโ and when is it used in A/B testing?

**Answer:**

The Bonferroni correction is a method to control the familywise error rate when conducting multiple comparisons. In A/B testing, itโs applied when analyzing multiple metrics or conducting multiple pairwise comparisons. It adjusts the significance level to account for the increased chance of Type I errors.

### 87. How do you handle โnon-normalityโ in A/B testing data?

**Answer:**

For non-normally distributed data, consider non-parametric tests like the Mann-Whitney U test or permutation tests. Alternatively, transformations or bootstrapping can be applied to approximate normality.

### 88. What is โrepeated measures designโ in A/B testing?

**Answer:**

Repeated measures design involves testing the same subjects under different conditions. Itโs useful when the same users are exposed to multiple variations, allowing for within-subject comparisons.

### 89. How do you account for โseasonalityโ in time-based experiments?

**Answer:**

To address seasonality, include seasonal indicators or use time series models to capture underlying patterns. This allows for a more accurate assessment of the treatmentโs impact.

### Code Snippet for Time Series Seasonal Decomposition (Python):

```
from statsmodels.tsa.seasonal import seasonal_decompose
def seasonal_decomposition(data, period):
result = seasonal_decompose(data, model='additive', period=period)
seasonal = result.seasonal
trend = result.trend
residual = result.resid
return seasonal, trend, residual
```

### 90. What is โblockingโ in experimental design and how does it apply to A/B testing?

**Answer:**

Blocking involves grouping participants based on specific characteristics before randomization. It helps control for potential confounding factors and ensures balance across treatment groups.

### 91. How do you handle โmissing dataโ in A/B testing?

**Answer:**

Address missing data by considering techniques like imputation or conducting sensitivity analyses to assess the potential impact of missing values on the results.

### 92. What is โsequential testingโ in the context of A/B testing?

**Answer:**

Sequential testing involves examining the results of an A/B test as data accumulates, rather than waiting until a fixed sample size is reached. It allows for early stopping if significant results are observed.

### 93. What is โcovariate adjustmentโ in A/B testing?

**Answer:**

Covariate adjustment involves incorporating additional variables (covariates) into the analysis to reduce noise and increase precision. It helps control for potential confounding factors and can lead to more accurate treatment effect estimates.

**Answer:**

For social platforms, consider techniques like network-based experiments or use methods that account for the interconnectedness of users. Graph-based models or propensity score matching with network features can be effective.

### 95. What is โpowerโ in the context of A/B testing?

**Answer:**

Power is the probability of detecting a true effect (i.e., rejecting the null hypothesis) when it exists. Itโs influenced by factors like sample size, effect size, and significance level. Higher power indicates a better chance of detecting real differences.

### 96. How do you handle โordinalโ or โcategoricalโ outcomes in A/B testing?

**Answer:**

For ordinal or categorical outcomes, apply techniques like ordinal regression or chi-squared tests. Ensure the chosen method aligns with the nature of the data and the research question.

### 97. What is โonline-to-offlineโ testing and when is it relevant?

**Answer:**

Online-to-offline testing involves assessing the impact of online interventions on offline behavior (e.g., online ad campaigns affecting in-store visits). Itโs relevant for businesses with both online and physical presences.

### 98. How do you address โcarryover effectsโ in A/B testing?

**Answer:**

Carryover effects occur when exposure to one variation influences the response to subsequent variations. Implement techniques like randomizing exposure sequences or incorporating a washout period to mitigate carryover effects.

**Answer:**

Bayesian Bandits is a sequential decision-making framework closely related to A/B testing. Itโs used in scenarios with multiple options and allows for continual learning and adaptation based on observed outcomes.

### 100. How do you handle โsmall sample sizesโ in A/B testing?

**Answer:**

With small sample sizes, consider techniques like bootstrapping or Bayesian methods which can provide more stable estimates. Additionally, focus on effect size and practical significance rather than relying solely on statistical significance.