Notes, summaries, assignments, exams, and problems for Mathematics

Introduction to Statistical Methods and Examples

Initial Setup and Data Visualization

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Key Concepts in Statistical Hypothesis Testing

Statistical Hypothesis

To reach decisions about populations based on sample information, we make certain assumptions about the populations involved. Such assumptions, which may or may not be true, are called statistical hypotheses.

Null Hypothesis (H₀) and Alternative Hypothesis (H₁)

The hypothesis formulated for the purpose of its rejection, under the assumption that it is true, is called the Null Hypothesis, denoted by H₀. The hypothesis complementary to the null hypothesis is called the Alternative Hypothesis, denoted by H₁.

Test of Significance

The process that helps us decide about the acceptance... Continue reading "Statistical Hypothesis Testing and Markov Chain Problem Solutions" »

Qualitative Variables

Nominal Variables

Nominal variables are qualitative variables that cannot be ordered in an ascending or descending manner; that is, they cannot be ranked. For example, blood group.

Ordinal Variables

Ordinal variables are variables that can be ordered in an ascending or descending manner; that is, they can be ranked.

Quantitative Variables

Discrete Variables

Discrete variables are variables whose values are obtained by counting.

Continuous Variables

Continuous variables are variables whose values are obtained by measurement using a scale.

Mean

Advantages

• Has many good theoretical properties
• Used as the basis of many statistical tests
• Good summary statistic for symmetrical distribution
• Easy to calculate
• Possible for further algebraic treatment

Disadvantages

• Less

Gestalt Psychology and Its Influence on UI Design

• Gestalt Psychology: An early 20th-century study focusing on the organizing principles of vision. Humans inherently seek patterns, a concept that significantly aids in User Interface (UI) design. For further reading, many visualization books cover this topic extensively.
• Gestalt Psychology: Understanding these innate patterns helps direct attention and organize information effectively. Utilize color and spacing strategically for impactful design.

Psychophysical Laws in Perception

• Weber's Law: States that the just-noticeable difference between two stimuli is proportional to their magnitude. This indicates that human perception operates based on percentage increases.
• Steven's Power Law: Describes the

Key Advantages of Bonds for Investors

Investing in bonds offers several key benefits:

• Source of Current Income: They are a good source of regular income.
• Relative Safety: Investment in bonds is relatively safe from large losses.
• Priority in Default: In case of default, bondholders receive their payments before shareholders can be compensated.

Comprehensive Bond Classification

Bonds are classified by their key features, which include:

• Form of Payment
• Coupon Payment
• Collateral
• Type of Circulation
• Type of Issuers
• Recall Possibility
• Place of Circulation
• Quality
• Other Miscellaneous Types

By Form of Payment

• Non-interest-bearing Bonds
• Regular Serial Bonds
• Deferred-interest Bonds
• Income Bonds
• Indexed Bonds
• Optional Payment Bonds

By Coupon Payment

• Coupon Bonds
• Zero-coupon Bonds
• Full

Understanding Kurtosis: Distribution Shape

Kurtosis is a statistical measure that describes the shape of a distribution’s tails compared to a normal distribution. It tells us whether the data are heavy-tailed or light-tailed.

In simple terms, kurtosis indicates the degree of peakedness and the presence of outliers in data.

Types of Kurtosis

• Mesokurtic: Normal distribution (kurtosis = 3).
• Leptokurtic: More peaked, heavy tails (kurtosis > 3).
• Platykurtic: Flatter peak, light tails (kurtosis < 3).

Key Concepts in Hypothesis Testing

1. Null Hypothesis (H₀)

It is a statistical statement that assumes no effect or no difference.

Example: “There is no difference between two groups.”

2. Alternative Hypothesis (H₁ / Hₐ)

It is the opposite of the... Continue reading "Key Statistical Concepts: Kurtosis & Hypothesis Testing" »

Caesar Cipher: Formal Representation

Plain alphabet: P = {sequence of plaintext letters}. Key: k ∈ {i | 0 ≤ i ≤ 25}. If k = 25, the shift maps a → z, b → a, and so on. Encryption: E(p) = (p + k) mod 26. Decryption: D(c) = (26 + c − k) mod 26.

Attacking the Caesar Cipher

Common methods to solve or attack a Caesar (shift) cipher include:

1. Brute force: Try all possible keys (0–25) and inspect the results.
2. Statistical (frequency) analysis: Use letter frequency distributions of the language to infer likely mappings.

Frequency Analysis: Basic Idea

Certain letters appear more frequently than others in a given language. By comparing ciphertext letter frequencies to natural language frequencies, you can match ciphertext characters to likely plaintext

Hypothesis Testing

Statistical Test Selection

1. If the population standard deviation is unknown and the sample size is less than 30: t-test

2. If the population standard deviation is known and the sample size is less than 30: t-test

7. Hypothesis test on population mean; n = 25; σ = 2.5: z-test

8. Hypothesis test on population mean; n = 50; s = 7.2: z-test

18. Test statistic for sample size above 30: z-test

19. Test statistic when population standard deviation is known: z-test

20. Test statistic when population standard deviation is unknown: t-test

21. When to use the t-test: I and II

24. Optimal sample size for z-test: Equal to or larger than 30

Hypotheses and Significance

3. H₀: μ = 30

4. H₁: μ > 30

5. No

9. False: The alternative hypothesis typically... Continue reading "Hypothesis Testing: A Concise Statistical Method Reference" »

What is Data Science?

• An interdisciplinary field combining statistics, computer science, and business knowledge.
• Its goal is to extract valuable insights and knowledge from data (both structured and unstructured).
• It answers key business questions: what happened, why, what will happen, and what to do about it.
• The process involves collecting, cleaning, processing, analyzing, and communicating data insights.

Statistical Inference: Making Educated Guesses

• It's the process of using sample data to make educated guesses or draw conclusions about a much larger population.
• Essentially, it lets you make generalizations about a whole group based on a smaller part of it.

Key Goals of Statistical Inference

• Estimation: To guess the value of a population parameter

Question 1: Decimal Representation of a Fraction

Question: Consider the fraction 6/7. The decimal representation of this fraction is:

Answer: 6 ÷ 7 = 0.857142857... (repeating)

Question 2: Vaccinated to Unvaccinated Ratio

Question: If 60% of a population is vaccinated, what is the ratio of vaccinated to unvaccinated individuals?

Answer: 60% vaccinated → 60 : 40 → Simplified = 3 : 2

Question 3: Property Tax Calculation

Question: A property has been assessed at $225,000. The mill rate is 14.5. To find the property tax, you would multiply the assessed value by:

Answer: The mill rate of 14.5 means $14.50 per $1,000 of assessed value. To convert this to a decimal factor, divide by 1,000:

• 14.5 ÷ 1,000 = 0.0145
• Property tax = $225,000 × 0.0145 = $3,262.

Executive Summary of Regression Models

• Simple Linear Regression: On average, for every 1-unit increase in [X], the expected [Y] changes by β1 units (95% CI: …).
• Multiplicative Model: On average, a 1-unit increase in [X] multiplies the median [Y] by exp(β1), resulting in a 100·(exp(β1)–1)% change (95% CI: …).
• Power Law/Elasticity: A 1% increase in [X] is associated with a β1% change in [Y] (95% CI: …).
• Categorical Variable: Students in Group A scored on average β1 units higher or lower than those in Group B (95% CI: …).
• Categorical Variable (3-Group): After adjusting for [X], students taught with Method 2 scored on average β1 units higher than those with Method 1; Method 3 scored β3 units lower.
• Interaction: For Group A, a 1-unit