# Data Analysts - Don't be Intimidated by Statistics - Statistical Concepts Made Simple

Statistics and data analysis are two related fields that involve the collection, analysis, interpretation, and presentation of data. Statistics is the science of collecting, organizing, analyzing, interpreting, and presenting data. It involves methods for describing and summarizing data, making inferences about populations based on sample data, and testing hypotheses using statistical tests. Statistics is used in a wide range of fields, including social sciences, natural sciences, engineering, and business. Data analysis, on the other hand, is the process of inspecting, cleaning, transforming, and modeling data to extract useful information and insights. Data analysis techniques include data mining, machine learning, and statistical modeling. Data analysis is used in a variety of applications, such as predictive analytics, business intelligence, and scientific research.

Statistics and data analysis are closely related, and they are often used together. Statistics provides the theoretical foundation for data analysis, while data analysis provides the tools and techniques for applying statistical methods to real-world problems. Together, these fields are used to make data-driven decisions and solve problems in a wide range of fields.

Source: https://thebittheories.com/data-analysis-and-statistical-inference-a-quick-guide-part-2-anova-87441c5018e5

So let’s get started with some statistical terminologies whose knowledge is important for a data analyst :

**1. Descriptive Statistics**

Descriptive statistics is a branch of statistics that involves the collection, organization, and presentation of data in a way that summarizes its main characteristics. Descriptive statistics provides a way to describe and summarize the data in a clear and meaningful way, without making any inferences or drawing any conclusions beyond the data itself.

Some common measures of descriptive statistics include:

**Measures of central tendency**, such as mean, median, and mode, which describe where the center of the data is located.**Measures of dispersion**, such as standard deviation and range, which describe how spread out the data is.**Measures of skewness and kurtosis**, which describe the shape of the distribution of the data.**Frequency distributions**, which show how often each value occurs in the data set.**Graphical representations of the data**, such as histograms and box plots, which provide a visual summary of the data.

Descriptive statistics is an important first step in analyzing data because it provides a clear and concise summary of the data, which can help to identify patterns, outliers, and other important features of the data. It can be used to summarize data from a single variable, or to compare data from multiple variables or groups.

**2. Variability in Statistics**

They are a set of descriptive statistics that describe the spread or dispersion of data around its central tendency. These statistics provide important information about the variability or consistency of a set of data. Some common measures of variability include:

**Range:**The difference between the maximum and minimum values in a dataset. It provides a simple measure of the spread of the data but can be sensitive to outliers.**Variance:**The average squared deviation of each data point from the mean. It provides a more precise measure of the spread of the data but can be difficult to interpret because it is in squared units.**Standard Deviation:**The square root of the variance. It provides a measure of the typical distance between each data point and the mean and is commonly used to describe the spread of normally distributed data.**Interquartile Range (IQR):**The difference between the 75th and 25th percentiles of the data. It provides a robust measure of the spread of the data that is less sensitive to outliers than the range.**Coefficient of Variation (CV):**The ratio of the standard deviation to the mean, expressed as a percentage. It provides a measure of the relative variability of the data, which can be useful when comparing data with different scales or units.

Variability statistics are important for understanding the range of values in a dataset and can be used to identify outliers or trends in the data.

**3. Correlation in Statistics**

Correlation in statistics are a set of statistical techniques used to measure the strength and direction of the relationship between two or more variables. Correlation statistics are important for understanding how variables are related to each other and for making predictions based on these relationships. Some common measures of correlation include:

**Pearson's correlation coefficient:**A measure of the linear relationship between two variables. The correlation coefficient ranges from -1 (indicating a perfect negative correlation) to +1 (indicating a perfect positive correlation), with 0 indicating no correlation.**Spearman's rank correlation coefficient:**A non-parametric measure of the monotonic relationship between two variables. The Spearman's correlation coefficient ranges from -1 to +1, with 0 indicating no correlation.**Kendall's rank correlation coefficient:**Another non-parametric measure of the monotonic relationship between two variables. The Kendall's correlation coefficient ranges from -1 to +1, with 0 indicating no correlation.

Correlation statistics can be used to analyze the relationship between any two quantitative variables, such as height and weight, or temperature and air pressure. Correlation analysis can be used in a wide range of fields, such as finance, marketing, and social sciences, to identify relationships between variables and make predictions based on these relationships. It is important to note that correlation does not imply causation. Just because two variables are correlated does not necessarily mean that one variable causes the other. It is important to consider other factors and use causal inference techniques to determine whether a causal relationship exists between two variables.

**4. Probability in Statistics**

In probability statistics, probability is defined as the likelihood of an event occurring. The probability of an event is a number between 0 and 1, where 0 indicates that the event is impossible and 1 indicates that the event is certain. The probability of an event A is denoted as P(A).

There are several common concepts in probability statistics, including:

**Random variables:**A random variable is a variable whose value is determined by a random process. Examples of random variables include the number of heads in a series of coin flips, the temperature in a room, or the number of cars passing through a particular intersection in an hour.**Probability distributions:**A probability distribution is a function that describes the likelihood of different outcomes of a random variable. Examples of probability distributions include the normal distribution, binomial distribution, and Poisson distribution.**Conditional probability:**Conditional probability is the probability of an event A given that another event B has occurred. It is denoted as P(A|B) and can be used to make predictions about the likelihood of future events.**Bayes' theorem:**Bayes' theorem is a formula that describes how to update the probability of an event based on new information or evidence.

Probability statistics is widely used in many fields, including statistics, machine learning, data science, and finance. It is an essential tool for making predictions, estimating risks, and making decisions under uncertainty.

**5. Regression Analysis in Statistics**

Regression analysis is a statistical technique used to analyze the relationship between a dependent variable (also known as the response variable) and one or more independent variables (also known as predictors). Regression analysis is used to make predictions and to understand the relationship between the variables. The most commonly used regression model is linear regression, which assumes that there is a linear relationship between the dependent variable and one or more independent variables. In a linear regression model, the goal is to find the line that best fits the data, where "best" is defined as the line that minimizes the sum of the squared differences between the predicted values and the actual values of the dependent variable.

There are many variations of the linear regression model, including:

**Multiple linear regression:**A regression model with more than one independent variable.**Polynomial regression:**A regression model that uses a polynomial function to describe the relationship between the dependent variable and the independent variable(s).**Logistic regression:**A regression model used to analyze the relationship between a binary dependent variable and one or more independent variables.**Time-series regression:**A regression model used to analyze the relationship between a dependent variable and time.

Regression analysis is used to make predictions about future outcomes and to understand the relationship between variables. Regression analysis is also used to test hypotheses and to determine whether the relationship between the variables is statistically significant.

**6. Normal Distribution in Statistics**

The normal distribution, also known as the Gaussian distribution, is a probability distribution that is widely used in statistics. It is a continuous probability distribution that is symmetrical and bell-shaped, with the mean, median, and mode all equal. The normal distribution is characterized by two parameters: the mean (µ) and the standard deviation (σ). The mean is the center of the distribution and the standard deviation measures the spread of the distribution. The normal distribution is often used to model natural phenomena such as heights, weights, and IQ scores, as well as errors in measurement.

The normal distribution has several important properties, including:

The total area under the curve is equal to 1.

The curve is symmetrical about the mean.

Approximately 68% of the data falls within one standard deviation of the mean, 95% falls within two standard deviations, and 99.7% falls within three standard deviations.

The normal distribution is widely used in statistical inference, including hypothesis testing, confidence intervals, and regression analysis. Many statistical methods assume that the data is normally distributed, and deviations from normality can lead to biased results. Therefore, it is important to check the normality assumption before applying certain statistical methods. The normal distribution is also important in probability theory, where it is used to describe the behavior of many random variables, such as the sum of a large number of independent random variables. The central limit theorem states that the sum of a large number of independent random variables will be approximately normally distributed, regardless of the distribution of the individual variables. This makes the normal distribution a fundamental concept in statistics and probability theory.

**6. Bias in Statistics**

Bias in statistics refers to a systematic error in the data or in the methods used to collect, analyze, or interpret the data. Bias can result in incorrect conclusions, and it can affect the reliability and validity of statistical analysis. Bias can arise from a variety of sources, including sampling methods, measurement tools, and human error.

Types of bias in statistics include:

1. **Sampling bias:** This occurs when the sample used in a study is not representative of the population. This can happen when the sample is selected using non-random methods or when the sample size is too small.
2. **Measurement bias: **This occurs when the measurement tool used in a study is inaccurate or flawed. This can happen when the tool is not calibrated correctly, or when there is inconsistency in how the tool is used.
3. **Observer bias:** This occurs when the observer's expectations or beliefs influence the measurements or observations. This can happen when the observer is aware of the hypothesis being tested, or when the observer has a preconceived notion of what the outcome should be.
4. **Publication bias:** This occurs when studies that find statistically significant results are more likely to be published than studies that do not. This can lead to an overestimation of the effect size or the strength of the relationship between variables.
5. **Confirmation bias:** This occurs when researchers or analysts interpret data in a way that confirms their preconceived beliefs or hypotheses. This can lead to the dismissal of contradictory evidence or the selection of data that supports a particular conclusion.

It is important to be aware of potential bias when conducting statistical analyses or interpreting statistical results. Researchers can use methods to minimize or correct for bias, such as random sampling, blind measurements, and peer review. Awareness of bias can lead to more accurate and reliable statistical analyses and conclusions.

**Conclusion**

These are common terminologies and concepts of statistics that a data analyst should have the knowledge of to perform better analysis , make improved data-driven decisions and solve problems in a broad range of disciplines. Hope some statistical concepts have been cleared and you enjoyed reading the blog!