What is a non-directional hypothesis?

A hypothesis that predicts there will be a difference or relationship between variables but does not specify the direction of that difference or relationship.

Why is a non-directional hypothesis also called a two-tailed hypothesis?

Because it allows for the possibility of results in either direction (both tails of a distribution), rather than predicting a specific direction of effect.

A researcher predicts that sleep deprivation will affect reaction time but is unsure whether it will make responses faster or slower. What type of hypothesis is this?

A non-directional (two-tailed) hypothesis, as it predicts an effect will occur without specifying the direction of that effect.

When might a researcher choose to use a non-directional hypothesis rather than a directional one?

When there is no prior research or theoretical basis to predict which direction the effect will go, or when previous findings have been contradictory.

Give an example of how a non-directional hypothesis might be worded for a study on caffeine and memory.

There will be a difference in memory performance between participants who consume caffeine and those who do not.

Edexcel A-Level Psychology 9PS0

Social Psychology

Topic overview Agency theory and social impact theory Milgram's research into obedience Factors affecting obedience and resistance Social identity theory and realistic conflict theory Factors affecting prejudice and discrimination Individual differences in obedience and prejudice Developmental psychology in obedience and prejudice Designing questionnaires and interviews Types of interview and question Alternate and null hypotheses Sampling techniques Quantitative and qualitative data Analysing quantitative data Thematic analysis of qualitative data The BPS code of ethics and conduct Risk management in psychological research Classic study: Sherif et al. (1954) Robbers Cave Contemporary study: Burger (2009)Contemporary study: Reicher and Haslam (2006)Contemporary study: Cohrs et al. (2012)Key question in social psychology Designing the practical investigation Analysing and reporting the practical investigation Ethics and practical issues in social psychology Nature-nurture, social control and reducing prejudice Reductionism and comparing explanations Culture, gender and social sensitivity

Cognitive Psychology

Topic overview The working memory model The multi-store model of memory Episodic and semantic long-term memory Reconstructive memory and schema theory Individual differences in memory Developmental psychology in memory Laboratory and field experiments Independent and dependent variables Experimental and null hypotheses One-tailed and two-tailed tests Experimental designs Operationalisation, extraneous and confounding variables Order effects and counterbalancing Situational and participant variables Objectivity, reliability and validity Demand characteristics and experimenter effects Measures of central tendency and dispersion Graphical presentation of data Mann-Whitney U and Wilcoxon Significance, critical values and errors Case studies of brain-damaged patients Classic study: Baddeley (1966)Contemporary study: Schmolck et al. (2002)Contemporary study: Steyvers and Hemmer (2012)Contemporary study: Sebastián and Hernández-Gil (2012)Key question in cognitive psychology Practical investigation in cognitive psychology Issues and debates in cognitive psychology

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Learning Theories

Topic overview The main features of classical conditioning Pavlov's experiment with salivation in dogs The main features of operant conditioning Properties and schedules of reinforcement Behaviour modification and shaping The main features of social learning theory The four stages of social learning Bandura's original Bobo doll experiments Bandura (1965) and vicarious reinforcement How learning theories explain phobias Systematic desensitisation and flooding Individual differences in learning theories Developmental psychology in learning theories Observational research with humans Animal research and its ethics Chi-squared and levels of measurement Thematic analysis in learning research The scientific status of psychology Classic study: Watson and Rayner (1920) Little Albert Contemporary study: Becker et al. (2002)Contemporary study: Bastian et al. (2011)Contemporary study: Capafons et al. (1998)Key question in learning theories Practical investigation in learning theories Issues and debates in learning theories

Clinical Psychology

Topic overview Diagnosing mental disorders and the four Ds The DSM and ICD classification systems Symptoms and features of schizophrenia Explanations of schizophrenia Anorexia nervosa: symptoms and explanations Obsessive-compulsive disorder: symptoms and explanations Unipolar depression: symptoms and explanations Treatments for schizophrenia and the second disorder Individual differences in clinical psychology Developmental psychology in clinical psychology HCPC guidelines for clinical practitioners Researching mental health Case studies in clinical psychology Interviews in clinical psychology Choosing an inferential test Descriptive statistics, levels of measurement and significance Thematic analysis and grounded theory Classic study: Rosenhan (1973)Contemporary study: Carlsson et al. (2000)Contemporary study: Kroenke et al. (2008)Contemporary study: Williams et al. (2013)Contemporary study: Scott-Van Zeeland et al. (2013)Contemporary study: Guardia et al. (2012)Contemporary study: Masellis et al. (2003)Contemporary study: March et al. (2004) POTS Key question in clinical psychology Practical investigation in clinical psychology Issues and debates in clinical psychology Comparing the classic studies

Criminological PsychologyApplication

Topic overview Biological explanations of crime Social explanations of crime The cognitive interview and ethical interviewing Psychological formulation and offence analysis Cognitive-behavioural treatments for offenders Biological treatments for offenders Factors influencing eye-witness testimony Factors influencing jury decision-making Individual differences in criminological psychology Developmental psychology in criminological psychology Research methods in criminological psychology Sample selection and techniques Reliability and validity in criminological research Objectivity, credibility and ethics in criminological research Analysing data and evaluating practical research Ethical guidelines in criminological research Classic study: Loftus and Palmer (1974)Contemporary study: Bradbury and Williams (2013)Contemporary study: Valentine and Mesout (2009)Contemporary study: Howells et al. (2005)Key question in criminological psychology Practical investigation in criminological psychology Issues and debates in criminological psychology

Child PsychologyApplication

Topic overview Bowlby's theory of attachment Ainsworth and the Strange Situation Research into deprivation Research into privation Research into day care Cross-cultural research into attachment Autism: features, explanations and therapies Individual differences in child psychology Developmental psychology in child psychology Observation in child psychology Questionnaires and interviews in child psychology Issues with self-report in child research Cross-cultural research methods The ethics of researching with children Analysing data in child psychology Classic study: van IJzendoorn and Kroonenberg (1988)Contemporary study: Cassibba et al. (2013)Contemporary study: Gagnon-Oosterwaal et al. (2012)Contemporary study: Li et al. (2013) child care timing Key question in child psychology Practical investigation in child psychology Issues and debates in child psychology

Health PsychologyApplication

Cognitive Psychology

One-tailed and two-tailed tests

4 things to know
Papers 1 and 3

Overview

Recall questions on directional and non-directional hypotheses and how to word them, when each is chosen, when one-tailed and two-tailed tests are used, and why a one-tailed test has more power at the same significance level.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

When is a two-tailed test used?

Evaluation

When is a two-tailed test appropriate?

Key term

What alternative name is given to a directional hypothesis?

Key term

When is a one-tailed test used?

Questions from this subtopic

Each one with the model answer underneath.

1
What alternative name is given to a directional hypothesis?
Model answer
A one-tailed hypothesis.
2
What is a non-directional hypothesis?
Model answer
A hypothesis that predicts there will be a difference or relationship between variables but does not specify the direction of that difference or relationship.
3
Why is a non-directional hypothesis also called a two-tailed hypothesis?
Model answer
Because it allows for the possibility of results in either direction (both tails of a distribution), rather than predicting a specific direction of effect.
4
A researcher predicts that sleep deprivation will affect reaction time but is unsure whether it will make responses faster or slower. What type of hypothesis is this?
Model answer
A non-directional (two-tailed) hypothesis, as it predicts an effect will occur without specifying the direction of that effect.
5
When might a researcher choose to use a non-directional hypothesis rather than a directional one?
Model answer
When there is no prior research or theoretical basis to predict which direction the effect will go, or when previous findings have been contradictory.
6
Give an example of how a non-directional hypothesis might be worded for a study on caffeine and memory.
Model answer
There will be a difference in memory performance between participants who consume caffeine and those who do not.

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