The LSAT features multiple types of evidence in Logical Reasoning arguments: Statistical/Empirical Evidence (numerical data from studies or research), Anecdotal Evidence (individual examples or personal experiences), Expert Testimony (opinions from authorities or specialists), Causal Evidence (claims about cause-and-effect relationships), Analogical Evidence (comparisons to similar situations), Survey/Poll Data (self-reported information from questionnaires), Scientific Studies (controlled experiments or systematic research), and Historical/Factual Evidence (past events or established facts). According to LSAC, "determining how additional evidence affects an argument" is one of the ten core skills tested in Logical Reasoning, making evidence evaluation central to LSAT success. Each evidence type has different strengths, appropriate uses, limitations, and typical flaws that appear repeatedly in LSAT arguments. Understanding these distinctions helps you evaluate argument quality and predict correct answers on Strengthen, Weaken, Assumption, and Flaw questions.

Statistical evidence uses numerical data from systematic observation, measurement, or research involving large samples to establish patterns, probabilities, or likelihood across populations. It's generally stronger because it's repeatable, verifiable, objective, and represents broader groups. Statistical evidence answers "How often?" "How likely?" and "What percentage?" Anecdotal evidence is based on individual examples, personal experiences, isolated incidents, or single cases—it shows that something is POSSIBLE but doesn't establish how LIKELY, PROBABLE, or TYPICAL it is. On the LSAT, the key distinction: statistical evidence supports generalizations and predictions about groups; anecdotal evidence only demonstrates possibility through single examples. A common LSAT flaw is using anecdotal evidence (one person's experience) to draw broad conclusions that require statistical support—this is called hasty generalization or unrepresentative sample. For example, "My grandfather smoked and lived to 95, therefore smoking isn't harmful" uses anecdotal evidence inappropriately to contradict statistical evidence. Statistical evidence is objective and independently verifiable, while anecdotal evidence is subjective, context-dependent, and can't be generalized. The LSAT frequently tests whether you recognize when arguments inappropriately generalize from anecdotal evidence or when they need statistical evidence to support their claims.

Evaluate LSAT evidence strength using these systematic criteria: 1) Evidence Type - Controlled scientific studies and statistical data are generally stronger than anecdotal examples or surveys. 2) Sample Size - Larger samples provide stronger evidence than small samples; a study of 10,000 participants is stronger than one with 10. 3) Representativeness - Evidence from representative, random samples generalizes better than biased or selective samples. 4) Relevance - Evidence must directly relate to the specific conclusion being drawn; strong but irrelevant evidence doesn't help. 5) Recency - Recent evidence is usually stronger than outdated data for current claims, especially in rapidly changing fields. 6) Source Credibility - Expert testimony from relevant fields is stronger than general authority or celebrity endorsement. 7) Methodology - Controlled experiments are stronger than observational studies; randomized trials are stronger than surveys; double-blind studies eliminate bias. 8) Consistency - Multiple independent pieces of supporting evidence are stronger than a single source. 9) Specificity - Specific, detailed evidence is stronger than vague generalizations. The LSAT tests whether you recognize when evidence is insufficient, inappropriately generalized, unrepresentative, irrelevant to the conclusion, or flawed in methodology.

Causal evidence on the LSAT is evidence presented to support a cause-and-effect claim—that X causes Y. LSAT arguments frequently make causal claims based on various types of evidence: correlation (X and Y occur together), temporal sequence (X precedes Y), controlled studies (manipulating X changes Y while controlling other variables), mechanism explanation (describing HOW X causes Y), or elimination of alternatives (ruling out other possible causes). The key LSAT insight: causal claims require strong evidence ruling out alternative explanations, reverse causation, and common causes. Mere correlation is weak causal evidence because correlation doesn't prove causation. Common causal reasoning flaws include: assuming correlation proves causation, failing to eliminate alternative causes, confusing cause and effect (reverse causation where Y actually causes X), overlooking potential common causes (Z causing both X and Y), and post hoc reasoning (assuming temporal sequence proves causation). Strengthening causal arguments requires evidence eliminating alternatives, demonstrating mechanism, or showing controlled manipulation of cause produces effect. Weakening causal arguments requires evidence showing alternative causes, reverse causation possibility, common cause affecting both, or cases where correlation breaks down (X without Y, or Y without X).

Expert testimony is evidence based on the opinion, judgment, or authority of someone with specialized knowledge, training, credentials, or experience in a relevant field. On the LSAT, expert testimony appears as statements from researchers, doctors, scientists, economists, engineers, or other specialists used to support conclusions. Key considerations for expert evidence strength: 1) Relevance of Expertise - The expert's field must directly relate to the claim being made (a medical doctor's opinion on economic policy isn't strong evidence; their opinion on medical treatments is). 2) Scope of Knowledge - Experts are authoritative only within their specialty; a physics expert isn't automatically an expert on biology. 3) Consensus vs. Individual Opinion - Expert consensus (multiple experts agreeing) is much stronger than a single expert opinion, especially if other experts disagree. 4) Potential Bias - Financial conflicts of interest, employment relationships, or personal stakes weaken expert testimony. 5) Evidence Base - Expert opinions supported by data and research are stronger than unsupported assertions. Common LSAT flaws with expert testimony: citing irrelevant expertise (expert outside their field), appeal to improper authority (citing fame or wealth instead of relevant credentials), treating expert opinion as proof rather than evidence, assuming experts can't disagree, or overlooking conflicts of interest that might bias the expert.

Analogical evidence uses comparison to support conclusions: because X is similar to Y in certain ways, and Y has property Z, therefore X probably has property Z too. LSAT arguments use analogies to predict outcomes, justify policies, support claims, or argue for similar treatment based on similar situations, cases, or examples. The strength of analogical evidence depends on: 1) Relevance of Similarities - The shared features must be relevant to the property being predicted; superficial similarities don't support conclusions. 2) Significance of Differences - Important, relevant differences weaken analogies even if some similarities exist. 3) Number of Relevant Similarities - More relevant similarities strengthen analogies; one similarity is weak. 4) Specificity - Specific, detailed similarities are stronger than vague resemblances. 5) Causal Connection - The similarities must actually relate to the predicted outcome. Common LSAT flaws with analogies: false analogies (comparing situations that aren't relevantly similar), ignoring significant differences (overlooking crucial dissimilarities), superficial similarity (basing conclusions on irrelevant resemblances), or overgeneralization (assuming all features transfer from one case to another). To strengthen analogical arguments, show additional relevant similarities and minimize differences. To weaken them, highlight significant relevant differences or show dissimilarities in key aspects. According to LSAC, "reasoning by analogy" is explicitly listed as one of the ten core skills tested in LSAT Logical Reasoning.

Survey data on the LSAT is evidence based on self-reported information collected through questionnaires, polls, or interviews. Surveys appear in arguments about opinions, preferences, behaviors, beliefs, or intentions. Survey evidence strength depends on: 1) Sample Size - Larger samples (1,000+) generally provide stronger evidence than small samples (less than 100). 2) Representativeness - The surveyed group must represent the population about which conclusions are drawn; surveying college students can't support conclusions about all adults. 3) Sampling Method - Random, stratified sampling is stronger than self-selected convenience samples. 4) Question Wording - Neutral, unbiased, clear questions produce more reliable results than leading, loaded, or ambiguous questions. 5) Response Rate - Low response rates suggest possible selection bias (only motivated people respond). 6) Honesty/Accuracy - Self-reports may be inaccurate due to social desirability bias, memory errors, or dishonesty. Common LSAT flaws with surveys: unrepresentative samples (surveying website visitors to conclude about general population), selection bias (only certain types of people respond), question bias (wording influences responses), social desirability bias (people answer what's socially acceptable, not truthful), or behavior-intent gap (what people say they'll do doesn't match what they actually do). Surveys are generally weaker than controlled studies but stronger than individual anecdotes.

Evidence is relevant on the LSAT when it directly relates to and has logical bearing on the specific conclusion being drawn—it makes the conclusion more or less likely. Evidence is irrelevant when it doesn't actually support or undermine the particular claim made, even if it's true, interesting, or related to the general topic. Key relevance factors: 1) Scope Match - Evidence must address the same scope as the conclusion (evidence about cats doesn't support conclusions about all animals; evidence about adults doesn't support conclusions about children). 2) Time Frame Match - Evidence from the relevant time period (past data may not support future predictions without additional assumptions about continuity). 3) Context Match - Evidence must apply to the specific context of the conclusion (evidence from one country may not apply to another with different conditions). 4) Property Match - Evidence about one characteristic doesn't necessarily support conclusions about different characteristics (evidence that X is popular doesn't support conclusions that X is effective). Common irrelevance patterns: evidence about different groups, evidence about different outcomes, evidence about different time periods, or evidence about correlation used to support causation conclusions. The LSAT frequently includes answer choices with strong but irrelevant evidence as trap answers. Always ask: Does this evidence actually make the SPECIFIC conclusion more or less likely, or does it just relate to the general topic?

To strengthen LSAT arguments with evidence, add information that makes the conclusion MORE likely to be true by: 1) Supporting Assumptions - Provide evidence confirming what the author takes for granted or assumes without stating. 2) Eliminating Alternatives - Rule out other explanations, causes, or possibilities that would undermine the conclusion. 3) Increasing Sample Size or Scope - Show patterns hold across larger, more diverse, or more representative groups. 4) Establishing Causation - Provide controlled studies, temporal sequence evidence, mechanism explanations, or elimination of alternative causes. 5) Confirming Analogies - Show additional relevant similarities between compared situations or minimize relevant differences. 6) Adding Expert Consensus - Provide supporting testimony from multiple relevant authorities or show field-wide agreement. 7) Demonstrating Representativeness - Show samples or examples are typical, not outliers or exceptions. 8) Providing Mechanism or Explanation - Explain HOW or WHY the claim would be true. Important: Strengthen answers don't have to PROVE the conclusion definitively, just make it MORE LIKELY or MORE REASONABLE. According to LSAC, "determining how additional evidence affects an argument" is a core tested skill. Practice identifying assumptions first, then look for evidence that would support those assumptions. Use official LSAC PrepTests from LawHub at lsac.org/lsat/prep to practice Strengthen questions with various evidence types from real LSAT administrations.

To weaken LSAT arguments with evidence, add information that makes the conclusion LESS likely to be true by: 1) Attacking Assumptions - Provide evidence showing what the author assumes is false, questionable, or unreliable. 2) Introducing Alternatives - Show other explanations, causes, or possibilities that make the conclusion less certain. 3) Revealing Sample Problems - Demonstrate samples are unrepresentative, biased, too small, or atypical. 4) Breaking Causal Claims - Show correlation without causation, reverse causation (effect causes supposed cause), or common causes (third factor causes both). 5) Undermining Analogies - Highlight significant relevant differences between compared situations. 6) Showing Expert Disagreement - Provide contrary expert opinions, show field disagreement, or reveal irrelevant expertise or bias. 7) Demonstrating Atypicality - Reveal that examples or data points are outliers, exceptions, or not typical cases. 8) Introducing Contrary Evidence - Provide data, studies, or examples that contradict the conclusion. Important: Weaken answers don't have to DISPROVE the conclusion completely, just make it LESS LIKELY or LESS CERTAIN. Common weakening patterns: For causal arguments, introduce alternative causes. For generalizations based on samples, show samples are unrepresentative. For predictions based on past patterns, show conditions changed or patterns don't continue. For analogies, show relevant differences. Always use official LSAC materials from LawHub at lsac.org/lsat/prep to practice Weaken questions with authentic evidence patterns from real LSAT tests.

Strong evidence on the LSAT is evidence that reliably supports conclusions, generalizes appropriately, comes from rigorous methodology, and has minimal inherent limitations. Characteristics include: large representative samples, controlled conditions, objective measurement, replicability, relevant expertise, statistical significance, and direct relevance to conclusions. Examples: randomized controlled trials, large-scale statistical studies from representative samples, consensus of relevant experts, controlled experiments with proper methodology. Weak evidence has significant limitations that reduce its ability to support conclusions. Characteristics include: small or unrepresentative samples, lack of controls, subjective measurement, inability to replicate, irrelevant authority, anecdotal nature, or indirect relevance. Examples: single anecdotal cases, small non-random samples, opinions from non-experts, surveys with biased samples or questions, correlation without causation, analogies with significant differences. Key LSAT principles: Evidence type matters—controlled studies trump anecdotes. Sample size and representativeness matter—10,000 subjects stronger than 10. Methodology matters—randomized trials stronger than surveys. Relevance matters—strong evidence in the wrong area doesn't help. Context matters—what's strong for one type of claim may be weak for another. The LSAT tests your ability to recognize when evidence is insufficient for the conclusion drawn, even if it's not completely worthless.