What is 'Sample Selection Bias'
Sample selection bias is a type of bias caused by choosing nonrandom data for statistical analysis. The bias exists due to a flaw in the sample selection process, where a subset of the data is systematically excluded due to a particular attribute. The exclusion of the subset can influence the statistical significance of the test, or produce distorted results.
BREAKING DOWN 'Sample Selection Bias'
Survivorship bias is a common type of sample selection bias. For example, when backtesting an investment strategy on a large group of stocks, it may be convenient to look for securities that have data for the entire sample period. If we were going to test the strategy against 15 years worth of stock data, we might be inclined to look for stocks that have complete information for the entire 15year period. However, eliminating a stock that stopped trading, or shortly left the market, would input a bias in our data sample. Since we are only including stocks that lasted the 15year period, our final results would be flawed, as these performed well enough to survive the market.

Sample
A subset containing the characteristics of a larger population. ... 
Sampling
A process used in statistical analysis in which a predetermined ... 
Systematic Sampling
A type of probability sampling method in which sample members ... 
Representative Sample
A subset of a statistical population that accurately reflects ... 
Simple Random Sample
A subset of a statistical population in which each member of ... 
Sampling Distribution
A probability distribution of a statistic obtained through a ...

Markets
What is Systematic Sampling?
Systematic sampling is similar to random sampling, but it uses a pattern for the selection of the sample. 
Markets
How Does Sampling Work?
Sampling is a term used in statistics that describes methods of selecting a predefined representative number of data from a larger data population. 
Markets
What is a Representative Sample?
In statistics, a representative sample accurately represents the makeup of various subgroups in an entire data pool. 
Markets
Understanding the Simple Random Sample
A simple random sample is a subset of a statistical population in which each member of the subset has an equal probability of being chosen. 
Investing
Explaining Standard Error
Standard error is a statistical term that measures the accuracy with which a sample represents a population. 
Managing Wealth
Behavioral Bias  Cognitive Vs. Emotional Bias In Investing
We all have biases. The key to better investing is to identify those biases and create rules to minimize their effect. 
Markets
Explaining the Central Limit Theorem
Central limit theorem is a fundamental concept in probability theory. 
Markets
How to Use Stratified Random Sampling
Stratified random sampling is a technique best used with a sample population easily broken into distinct subgroups. Samples are then taken from each subgroup based on the ratio of the subgroup’s ... 
Investing
8 Common Biases That Impact Investment Decisions
Behavioral biases hit us all as investors and can vary depending upon our investor personality type. 
Markets
Top Reasons Stock Indices Could Be Biased
Do the owners of the large stock indices (McGraw Hill Financial, CME Group, and News Corp) have incentive to pick stocks to put in the index that are "shiny" as a marketing ploy? And if so, wouldn't ...

How can a representative sample lead to sampling bias?
Learn how using representative samples alone is not enough to make sampling bias negligible and why elements such as randomization ... Read Answer >> 
What percentage of the population do you need in a representative sample?
Learn about representative samples and how they are used in conjunction with other strategies to create useful data with ... Read Answer >> 
What is the difference between systematic sampling and cluster sampling?
Learn about the differences between systematic sampling and cluster sampling, including how the samples are created for each ... Read Answer >> 
What are the benefits of financial sampling?
Learn more about how financial sampling is used to determine whether or not inaccurate or fraudulent information exists in ... Read Answer >> 
What's the difference between a representative sample and a convenience sample?
Learn the difference between convenience sampling and representative sampling and the advantages and disadvantages of each ... Read Answer >> 
What's the difference between a representative sample and a random sample?
Explore the differences between representative samples and random samples, and discover how they are often used in tandem ... Read Answer >>