Internet Mental Health


  • Phencyclidine use disorder is the continued use of phencyclidine despite clinically significant distress or impairment.

  • Typically includes a strong desire to take the drug, difficulties in controlling its use, persisting in its use despite harmful consequences, a higher priority given to drug use than to other activities and obligations, and increased tolerance.


    Episodic or continuous for years


Occupational-Economic Problems:

  • Significant academic, occupational or social impairment

Disinhibited (Disinhibition):

  • Intoxicated behavior, impaired driving

  • Impulsivity, dangerous risk taking, irresponsibility

  • Violent behavior

Psychotic (Impaired Intellect):

  • Intoxication causes severe changes in body image, loss of ego boundaries, paranoia, depersonalization, hallucinations

  • Hallucinations may last for weeks and may trigger a persistent psychotic episode resembling Schizophrenia

  • Paranoid delusions can lead to bizarre acts of violence (e.g. the case of the phencyclidine intoxication of Big Lurch, a former rapper who, thinking that his room mate was the devil, killed her and ate part of her lung)

  • Chronic use causes impairment in memory, speech, and cognition that may last for months

  • May induce feelings of strength, power, and invulnerability as well as a numbing effect on the mind

  • Low doses cause dissociative symptoms (feelings of separation from mind and body); high doses can cause stupor and coma

Sociable (High Extraversion):

  • Intoxication causes euphoria

Emotional Distress (Negative Emotion):

  • Intoxication can cause suicidal impulses


  • Denial of addiction

  • Intoxication causes numbness in the extremities, staggering, unsteady gait, slurred speech, bloodshot eyes, and loss of balance; higher doses produce analgesia, anesthesia and convulsions

  • Injuries/death from accidents, fights, falls or erratic behavior during a "bad trip"

  • Cardiovascular and neurological toxicities (e.g., seizures, dystonias, dyskinesias, catalepsy, hypothermia or hyperthermia)

  • Intracranial hemorrhage, rhabdomyolysis, respiratory problems, and cardiac arrest

Back to top

Diagnose Phencyclidine Use Disorder

Limitations of Self-Diagnosis

Self-diagnosis of this disorder is often inaccurate. Accurate diagnosis of this disorder requires assessment by a qualified practitioner trained in psychiatric diagnosis and evidence-based treatment.

However, if no such professional is available, our free computerized diagnosis is usually accurate when completed by an informant who knows the patient well. Computerized diagnosis is less accurate when done by patients (because they often lack insight).

Example Of Our Computer Generated Diagnostic Assessment

Phencyclidine Use Disorder 304.60

This diagnosis is based on the following findings:
  • Abused phencyclidine in the past 5 years (still present)
  • Greater use of phencyclidine than intended (still present)
  • There is a persistent desire or unsuccessful efforts to cut down or control use of phencyclidine (still present)
  • A great deal of time is spent in obtaining phencyclidine, using it, or recovering from its effects (still present)
  • Craving, or a strong desire or urge to use phencyclidine (still present)
  • Recurrent use of phencyclidine resulting in a failure to fulfill major role obligations at work, school or home (still present)
  • Continued use of phencyclidine despite having persistent social problems that it made worse (still present)
  • Important social, occupational, or recreational activities are given up or reduced because of phencyclidine use (still present)
  • Developed tolerance to phencyclidine (still present)

Treatment Goals:

  • Goal: stop using phencyclidine because using more than intended.

  • Goal: stop using phencyclidine because it is getting out of control.

  • Goal: stop using phencyclidine in order to prevent wasting so much time using this substance, or recovering from its use.

  • Goal: stop using phencyclidine in order to decrease craving for this substance.

  • Goal: stop using phencyclidine so that she can better fulfill major role obligations at work, school or home.

  • Goal: stop using phencyclidine in order to improve the phencyclidine-related social problems.

  • Goal: stop using phencyclidine in order to increase time spent on important social, occupational, or recreational activities.

  • Goal: stop using phencyclidine in hazardous situations in order to prevent injury.

  • Goal: stop using phencyclidine in order to prevent further worsening of current phencyclidine-related physical or emotional problems.

  • Goal: stop using phencyclidine because tolerance to this substance is developing.

Back to top

Dependence Syndrome Due To Use Of Phencyclidine F19 - ICD10 Description, World Health Organization
Repeated use of phencyclidine that typically includes a strong desire to take the drug, difficulties in controlling its use, persisting in its use despite harmful consequences, a higher priority given to drug use than to other activities and obligations, and increased tolerance.
Phencyclidine Use Disorder - Diagnostic Criteria, American Psychiatric Association

An individual diagnosed with Phencyclidine Use Disorder needs to meet all of the following criteria:

  • A pattern of phencyclidine (or a pharmacologically similar substance) use leading to clinically significant impairment or distress, as manifested by at least two of the following, occurring within a 12-month period:

    • Phencyclidine is often taken in larger amounts or over a longer period than was intended.

    • There is a persistent desire or unsuccessful efforts to cut down or control phencyclidine use.

    • A great deal of time is spent in activities necessary to obtain phencyclidine, use phencyclidine, or recover from its effects.

    • Craving, or a strong desire or urge to use phencyclidine.

    • Recurrent phencyclidine use resulting in a failure to fulfill major role obligations at work, school, or home (e.g., repeated absences from work or poor work performance related to hallucinogen use; phencyclidine-related absences, suspensions, or expulsions from school; neglect of children or household).

    • Continued phencyclidine use despite having persistent or recurrent social or interpersonal problems caused or exacerbated by the effects of phencyclidine (e.g., arguments with a spouse about consequences of intoxication; physical fights).

    • Important social, occupational, or recreational activities are given up or reduced because of phencyclidine.

    • Recurrent phencyclidine use in situations in which it is physically hazardous (e.g., driving an automobile or operating a machine when impaired by phencyclidine).

    • Phencyclidine use is continued despite knowledge of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by phencyclidine.

    • Tolerance, as defined by either of the following:

      • A need for markedly increased amounts of phencyclidine to achieve intoxication or desired effect.

      • A markedly diminished effect with continued use of the same amount of phencyclidine.

      Note: Withdrawal symptoms and signs are not established for phencyclidine, and so this criterion does not apply.

    • Specify if:

      • In early remission: After full criteria for Phencyclidine Use Disorder were previously met, none of the criteria for Phencyclidine Use Disorder have been met for at least 3 months but for less than 12 months (with the exception that the criterion, "Craving, or a strong desire or urge to use phencyclidine," may be met).

      • In sustained remission: After full criteria for Phencyclidine Use Disorder were previously met, none of the criteria for Phencyclidine Use Disorder have been met at any time during a period of 12 months or longer (with the exception that the criterion, "Craving, or a strong desire or urge to use the hallucinogen," may be met).

    • Specify if:

      • In a controlled environment: This additional specifier is used if the individual is in an environment where access to phencyclidine is restricted.

Back to top

Diagnostic Features

The phencyclidine-like substances include phencyclidine (PCP or angel dust) and less potent but similarly acting compounds such as ketamine, cyclohexamine, and dizocilpine. These drugs produce feelings of separation from mind and body (i.e., are "dissociative") in low doses, and at high doses, stupor and coma can result.

Phencyclidine Use Disorder is a condition characterized by the harmful consequences of repeated use of phencyclidine-like drugs, a pattern of compulsive use of phencyclidine-like drugs, and (sometimes) physiological dependence on phencyclidine-like drugs (i.e., tolerance). This disorder is only diagnosed when the use of phencyclidine-like drugs becomes persistent and causes significant academic, occupational, social or medical impairment.

Phencyclidine Intoxication causes significant psychological and social impairment (e.g., belligerence, assaultiveness, impulsiveness, unpredictability, psychomotor agitation, impaired judgment, or impaired social or occupational functioning). Two or more of the following signs develop: vertical or horizontal nystagmus, hypertension or tachycardia, numbness or diminished responsiveness to pain, ataxia, dysarthria, muscle rigidity, seizures or coma, hyperacusis.

Drug effects begin almost immediately after intravenous use or smoking, reaching a peak within minutes. Peak effects occur about 2 hours after oral doses. In milder intoxications, the effects resolve after 8-20 hours, whereas severe intoxications may persist for several days. Phencyclidine-Induced Psychotic Disorder may persist for weeks.

Lower doses of phencyclidine produce: vertigo, ataxia, nystagmus, mild hypertension, abnormal involuntary movements, slurred speech, nausea, weakness, slowed reaction times, euphoria or emotional dulling, and lack of concern. Intermediate doses of phencyclidine produce: disorganized thinking, charged body image and sensory perception, depersonalization, and feelings of unreality. Higher doses of phencyclidine produce: amnesia and coma, with analgesia sufficient for surgery, and seizures with respiratory depression.

There does not appear to be a phencyclidine withdrawal syndrome.


Phencyclidine Intoxication can cause delirium, coma, psychotic symptoms, or catatonic mutism with posturing. Phencyclidine users are often arrested for violence, agitation, or bizarre behavior (e.g., confused wandering). The case of Big Lurch, a former rapper, illustrates how bizarre phencyclidine intoxication can become. While using phencyclidine, Big Lurch thought his room mate was the devil, butchered her, and ate part of her lung. Chronic use of phencyclidine may lead to deficit in memory, speech, and thinking that can last for months. Phencyclidine may cause cardiovascular and neurological toxicities (e.g., seizures, dystonias, dyskinesias, catalepsy, hypothermia or hyperthermia). Other complications include intracranial hemorrhage, rhabdomyolysis, respiratory problems, and occasionally cardiac arrest. Phencyclidine can trigger an increase in psychotic symptoms in Schizophrenia.


Individuals with Phencyclidine Use Disorder usually have multiple other Substance Use Disorders. This disorder commonly co-occurs with Antisocial Personality Disorder. Recurring episodes of psychotic or mood symptoms due to Phencyclidine Intoxication may mimic Schizophrenia or Mood Disorders. History or laboratory evidence of phencyclidine use does not rule out the co-occurrence of Schizophrenia or Mood Disorders. Rapid onset of symptoms, presence of delirium, or observation of nystagmus or hypertension suggests phencyclidine intoxication rather than Schizophrenia, but phencyclidine can trigger a psychotic episode in Schizophrenia. Rapid resolution of symptoms suggests that the symptoms are due to phencyclidine, and not to Schizophrenia or a Mood Disorder.

Associated Laboratory Findings

Phencyclidine can be detected on routine toxicological urine tests for several weeks after the end of prolonged or very high dose use. Creatinine phosphokinase (CPK) and serum glutamic-oxaloacetic transaminase (SGOT) are often elevated due to muscle damage.


The prevalence of Phencyclidine Use Disorder is unknown. What is known is that 0.3% of 12- to 17-year-olds, 1.3% of 18- to 25-year-olds, and 2.9% of those aged 26 years and older report ever using phencyclidine. Males make up 75% of those with phencyclidine-related emergency room visits.


The outcome of Phencyclidine Use Disorder is unknown.

Familial Pattern

Research from other hallucinogen use disorders suggests that genetics may play a large part in the occurrence of this disorder. Many individuals with hallucinogen use disorders have genetic behavioral disinhibition (a highly heritable tendency towards impulsivity, novelty-seeking, dangerous risk-taking and rule-breaking).

Effective Therapies

Management of PCP intoxication mostly consists of supportive care and treatment of anxiety or agitation with lorazepam, and treatment of psychosis with atypical antipsychotic medication. The effectiveness of treatment for phencyclidine dependence is unknown due to lack of randomized, controlled clinical trials.

It is possible to stop using phencyclidine. To do this you must: (1) totally divorce yourself from drug-using or drug-supplying people, (2) not use alcohol or any other illegal drug, (3) keep socially active and help others, (4) talk to other people who have successfully stayed off drugs, (5) devote yourself to important activities that gives meaning and purpose to life (e.g., family, friends, sports, work, helping others, church etc.). Therapists know that these 5 steps work, but our therapies are often ineffective in motivating patients to complete these essential steps to recovery.

Top 20 Most Harmful Drugs In Britain In 2008

Professor David Nutt published in the Lancet the following rating of Britain's most dangerous drugs. They are listed in descending order from the most harmful.

1. Heroin

Class A drug. Originally used as a painkiller and derived from the opium poppy. There were 897 deaths recorded from heroin and morphine use in 2008 in England and Wales, according to the Office of National Statistics (ONS). There were around 13,000 seizures, amounting to 1.6m tonnes of heroin.

2. Cocaine

Class A. Stimulant produced from the South American coca leaf. Accounted for 235 deaths -- a sharp rise on the previous year's fatalities. Nearly 25,000 seizures were made, amounting to 2.9 tonnes of the drug.

3. Barbiturates

Class B. Synthetic sedatives used for anaesthetic purposes. Blamed for 13 deaths.

4. Street methadone

Class A. A synthetic opioid, commonly used as a substitute for treating heroin patients. Accounted for 378 deaths and there were more than 1,000 seizures of the drug.

5. Alcohol

Subject to increasing concern from the medical profession about its damage to health. According to the ONS, there were 8,724 alcohol deaths in the UK in 2007. Other sources claim the true figure is far higher.

6. Ketamine

Class C. A hallucinogenic dance drug for clubbers. There were 23 ketamine-related deaths in the UK between 1993 and 2006. Last year there were 1,266 seizures.

7. Benzodiazepines

Class C. A hypnotic relaxant used to treat anxiety and insomnia. Includes drugs such as diazepam, temazepam and nitrazepam. Caused 230 deaths and 1.8m doses were confiscated in more than 4,000 seizure operations.

8. Amphetamine

Class B. A psychostimulant that combats fatigue and suppresses hunger. Associated with 99 deaths, although this tally includes some ecstasy deaths. Nearly 8,000 seizures, adding up to almost three tonnes of confiscated amphetamines.

9. Tobacco

A stimulant that is highly addictive due to its nicotine content. More than 100,000 people a year die from smoking and tobacco-related diseases, including cancer, respiratory diseases and heart disease.

10. Buprenorphine

An opiate used for pain control, and sometimes as a substitute to wean addicts off heroin. Said to have caused 43 deaths in the UK between 1980 and 2002.

11. Cannabis

Class B. A psychoactive drug recently appearing in stronger forms such as "skunk". [Since this video was made; there is now conclusive proof that cannabis causes a 6.7 fold increase in the risk of developing schizophrenia.] Caused 19 deaths and there were 186,000 seizures, netting 65 tonnes of the drug and 640,000 cannabis plants.

12. Solvents

Fumes inhaled to produce a sense of intoxication. Usually abused by teenagers. Derived from commonly available products such as glue and aerosol sprays. Causes around 50 deaths a year.

13. 4-MTA

Class A. Originally designed for laboratory research. Releases serotonin in the body. Only four deaths reported in the UK between 1997 and 2004.

14. LSD

Class A. Hallucinogenic drug originally synthesised by a German chemist in 1938. Very few deaths recorded.

15. Methylphenidate

Class B drug. Brand name of Ritalin. A psychostimulant sometimes used in the treatment of attention deficit disorders.

16. Anabolic steroids

Class C. Used to develop muscles, notably in competitive sports. Also alleged to induce aggression. Have been blamed for causing deaths among bodybuilders. More than 800 seizures.

17. GHB

Class C drug. A clear liquid dance drug said to induce euphoria, also described as a date rape drug. Can trigger comas and suppress breathing. Caused 20 deaths and 47 seizures were recorded.

18. Ecstasy

Class A. Psychoactive dance drug. Caused 44 deaths, with around 5,000 seizures made.

19. Alykl nitrites

Known as "poppers". Inhaled for their role as a muscle relaxant and supposed sexual stimulant. Reduce blood pressure, which can cause fainting and in some cases death.

20. Khat

A psychoactive plant, the leaves of which are chewed in east Africa and Yemen. Also known as qat. Produces mild psychological dependence. Its derivatives, cathinone and cathine, are Class C drugs in the UK.

Ineffective therapies

Some argue that phencyclidine use should be decriminalized, and that phencyclidine addiction should be treated "like any other medical disorder". They forget that there is no treatment for Phencyclidine Use Disorder that has been proven effective.

Legalizing Illicit Drugs

Some people argue that illicit drugs should be legalized to decrease the crime associated with these drugs. Historically, tobacco and alcohol were once illegal drugs. Tobacco smoking is now the leading cause of death in America, and alcoholism is the third leading cause of death. Thus legalizing illicit drugs does not make them any less medically and socially harmful. In fact the opposite is true; legalizing illicit drugs increases their use and the harm they cause. The Government of Finland is passing legislation that will gradually ban all tobacco use by 2040.

Back to top

Man psychotic on PCP drives through crowd of tourists in Times Square

Dr. Rabach: Phencyclidine (Angel Dust)

Dr. Gardere: Addiction


Rating Scales

    Stages of Learned Behavior

    Our survival involves learning what to avoid (i.e., fear) and what to approach (i.e., crave). Both fear and craving are essential for our survival, but both can spiral out of control.

    For example, an individual can develop a phobia about snakes in which the fear becomes excessive. This phobia can develop into an obsession in which the individual spends much of the time thinking about snakes, and how to avoid them.

    This obsession can develop into a compulsion in which the individual spends much of the time doing superstitious, compulsive, ritual behaviors aimed at avoiding snakes.

    Likewise, an individual can develop an excessive craving for alcohol which causes significant distress or disability.

    This excessive craving for alcohol can develop into an obsession in which the individual spends much of the time thinking about alcohol, and how to get it.

    This obsession can develop into a compulsion in which the individual spends much of the time compulsively drinking, and feeling powerless to resist this craving.

    Four Stages of Fear and Craving

    Normal Fear:
    Is in proportion to the actual danger, and doesn't cause significant distress or disability.
    Normal Craving:
    Doesn't cause significant distress or disability.
    Excessive Fear (Phobia):
    Is out of proportion to the actual danger posed, and causes significant distress or disability.
    Excessive Craving:
    Is not socially acceptable, and causes significant distress or disability (e.g., "I'm using [alcohol] too much").
    Obsessional Fear:
    Persistent, unwanted or obsessional thoughts about the fear develop, which cause significant distress or disability.
    Obsessional Craving:
    Persistent, unwanted or obsessional thoughts about the craving develop, which cause significant distress or disability (e.g., "I spend much of my time thinking about [alcohol], and how to get it").
    Compulsive Fear:
    Compulsive behaviors develop (aimed at reducing the anxiety associated with the obsession), which the individual finds very hard to resist doing.
    Compulsive Craving:
    Compulsive behaviors develop (aimed at satisfying the craving), which the individual finds very hard to resist doing (e.g., "I can't stop myself from using [alcohol]").

Back to top

World Health Organization Drug Use Disorder Treatment Guidelines

Treatment Guidelines

Treatment Research

  • Does Teen Drug Rehab Cure Addiction or Create It?
  • International Guidelines for the Evaluation of Treatment Services and Systems for Psychoactive Substance Use Disorders - World Health Organization
  • Crime

    Back to top

    Overcoming Drug Addiction

    Self-Help Groups for Drug Addiction

    Monitoring Your Progress

    NOTE: When each of the following presentations finish; you must exit by manually closing its window in order to return to this webpage.

    The Healthy Social Behavior Scale lists social behaviors that research has found to be associated with healthy social relationships. You can keep score (totaling its 4-point scale answers) on a separate piece of paper to monitor your progress.

    The Mental Health Scale lists behaviors and symptoms that research has found to be associated with mental health (or disorder). You can keep score (totaling its 4-point scale answers) on a separate piece of paper to monitor your progress.

    The Life Satisfaction Scale lists the survey questions often used to measure overall satisfaction with life. You can keep score (totaling its 4-point scale answers) on a separate piece of paper to monitor your progress.

    Life Satisfaction Scale (5-Minute Video)

    The "Big 6" Dimensions of Mental Health

    Research has shown that there are 5 major dimensions (the "Big 5 Factors" or Five-Factor Model) of personality disorders and other mental disorders.

    This website uses these 5 major dimensions of human behavior (i.e., Agreeableness, Conscientiousness, Openness/Intellect, Extraversion/Sociability, and Emotional Stability) to describe all mental disorders. This website adds one more dimension, "Physical Health", to create the "Big 6" dimensions of mental health.

    The behaviors of the "Five Factor Model of Personality" represent five adaptive functions that are vital to human survival. For example, when one individual approaches another, the individual must: (1) decide whether the other individual is friend or foe [ "Agreeableness" ], (2) decide if this represents safety or danger [ "Emotional Stability" ], (3) decide whether to approach or avoid the other individual [ "Extraversion/Sociability" ], (4) decide whether to proceed in a cautious or impulsive manner [ "Conscientiousness" ], and (5) learn from this experience [ "Openness/Intellect" ].

    Desiderata (5-Minute Video)

    The following "Morning Meditation" allows you to plan your day using these "Big 6" dimensions of mental health.

    The following "Evening Meditation" allows you to review your progress on these "Big 6" dimensions of mental health.

    Back to top

      "In physical science a first essential step in the direction of learning any subject is to find principles of numerical reckoning and practicable methods for measuring some quality connected with it. I often say that when you can measure what you are speaking about and express it in numbers you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind: it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science, whatever the matter may be."

      Lord Kelvin (1824 – 1907)

    • The best summary on bad research is given by Laura Arnold in this TEDx lecture. If you read nothing else about research, you owe it to yourself to watch this short video - it is excellent!

    • Economist in grim battle against deceptive scholarship

    • List of Predatory Journals and Publishers

    • The power of asking "what if?"

    • The active placebo effect: 2300 years ago, the Greek Stoic philosophers taught that it is not the objective event, but our subjective judgment about the event, that determines our behavior. The active placebo effect bears witness to this ancient wisdom.

    • Criteria For High Quality Research Studies

    • It is troubling that a recent study found that two-thirds of important psychological research studies couldn't be replicated. High quality research must meet the following criteria:

      • Randomized Controlled Trial:
        Ask: Was the trial randomized? Was the randomization procedure described and was it appropriate? The best research design is to have research subjects randomly assigned to an experimental or control group. It is essential that confounding factors be controlled for by having a control group or comparator condition (no intervention, placebo, care as usual etc.).

      • Representative Sample:
        Ask: Do the research subjects represent a normal cross-section of the population being studied? Many psychological research studies using university students are flawed because their subjects are not representative of the normal population since they are all W.E.I.R.D. (White, Educated, Intelligent, Rich, and living in a Democracy).

      • Single Blind Trial:
        Ask: Was the treatment allocation concealed? It is essential that the research subjects are kept "blind" as to whether they are in the experimental or control group (in order to control for any placebo effects).

      • Double Blind Trial (Better Than Single Blind Trial):
        Ask: Were blind outcome assessments conducted? In a double blind study, neither the research subjects nor the outcome assessors know if the research subject is in the experimental or control group. This controls for both the placebo effect and assessor bias.

      • Baseline Comparability:
        Ask: Were groups similar at baseline on prognostic indicators? The experimental and control groups must be shown to be comparable at the beginning of the study.

      • Confounding Factors:
        Ask: Were there factors, that weren't controlled for, that could have seriously distorted the study's results? For example, research studies on the effectiveness of mindfulness cognitive therapy in preventing depressive relapse forgot to control for whether the research subjects were also simultaneously receiving antidepressant medication or other psychological treatments for depression.

      • Intervention Integrity:
        Ask: Was the research study protocal strictly followed? The research subjects must be shown to be compliant (e.g., taking their pills, attending therapy) and the therapists must be shown to be reliably delivering the intervention (e.g., staying on the research protocol).

      • Statistical analysis:
        Ask: Was a statistical power calculation described? The study should discuss its statistical power analysis; that is whether the study size is large enough to statistically detect a difference between the experimental and control group (should it occur) and usually this requires at least 50 research subjects in the study.

        Ask: Are the results both statistically significant and clinically significant? Many medical research findings are statistically significant (with a p-value <0.05), but they are not clinically significant because the difference between the experimental and control groups is too small to be clinically relevant.

        For example, the effect of a new drug may be found to be 2% better than placebo. Statistically (if the sample size was large enough) this 2% difference could be statistically significant (with a p-value <0.05). However, clinicians would say that this 2% difference is not clinically significant (i.e., that it was too small to really make any difference).

        Statistically, the best way to test for clinical significance is to test for effect size (i.e., the size of the difference between two groups rather than confounding this with statistical probability).

        When the outcome of interest is a dichotomous variable, the commonly used measures of effect size include the odds ratio (OR), the relative risk (RR), and the risk difference (RD).

        When the outcome is a continuous variable, then the effect size is commonly represented as either the mean difference (MD) or the standardised mean difference (SMD) .

        The MD is the difference in the means of the treatment group and the control group, while the SMD is the MD divided by the standard deviation (SD), derived from either or both of the groups. Depending on how this SD is calculated, the SMD has several versions such, as Cohen's d, Glass's Δ, and Hedges' g.

          Clinical Significance: With Standard Mean Difference, the general rule of thumb is that a score of 0 to 0.25 indicates small to no effect, 0.25-0.50 a mild benefit, 0.5-1 a moderate to large benefit, and above 1.0 a huge benefit. It is a convention that a SMD of 0.5 or larger is a standard threshold for clinically meaningful benefit.

        The statistical summary should report what percentage of the total variance of the dependent variable (e.g., outcome) can be explained by the independent variable (e.g., intervention).

        In clinical studies, the study should report the number needed to treat for an additional beneficial outcome (NNTB), and the number needed to treat for an additional harmful outcome (NNTH).

          Number Needed To Benefit (NNTB): This is defined as the number of patients that need to be treated for one of them to benefit compared with a control in a clinical trial. (It is defined as the inverse of the absolute risk reduction.) Note: Statistically, the NNTB depends on which control group is used for comparison - e.g., active treatment vs. placebo treatment, or active treatment vs. no treatment.

          Number Needed To Harm (NNTH): This is defined as the number of patients that need to be treated for one of them to be harmed compared with a control in a clinical trial. (It is defined as the inverse of the absolute increase in risk of harm.)

          Tomlinson found “an NNTB of 5 or less was probably associated with a meaningful health benefit,” while “an NNTB of 15 or more was quite certain to be associated with at most a small net health benefit.”

        Ask: Does the researcher accept full responsibility for the study's statistical analysis? The researcher should not just hand over the study's raw data to a corporation (that may have $1,000 million invested in the study) to do the statistical analysis.

      • Completeness of follow-up data:
        Ask: Was the number of withdrawals or dropouts in each group mentioned, and were reasons given for these withdrawals or dropouts? Less than 20% of the research subjects should drop out of the study. The intervention effect should persist over an adequate length of time.

      • Handling of missing data:
        Ask: Was the statistical analysis conducted on the intention-to-treat sample? There must be use of intention-to-treat analysis (as opposed to a completers-only analysis). In this way, all of the research subjects that started the study are included in the final statistical analysis. A completers-only analysis would disregard those research subjects that dropped out.

      • Replication of Findings:
        Ask: Can other researchers replicate this study's results? The research study's methodology should be clearly described so that the study can be easily replicated. The researcher's raw data should be available to other researchers to review (in order to detect errors or fraud).

      • Fraud:
        Ask: Is there a suspicion of fraud? In a research study, examine the independent and dependent variables that are always measured as a positive whole number (e.g., a variable measured on a 5-point Likert-type scale ranging from "1 = definitely false to 5 = definitely true" etc.). For each of these variables, look at their sample size ( n ), mean ( M ) and standard deviation ( SD ) before they undergo statistical analysis. There is a high suspicion of fraud in a study's statistics:

        • If the M is mathematically impossible (online calculator): This is one of the easiest ways to mathematically detect fraud. The mean ( M ) is defined as "the sum ( Sum ) of the values of each observation divided by the total number ( n ) of observations". So: M = Sum / n . Thus: ( Sum ) = ( M ) multiplied by ( n ). We know that, if a variable is always measured as a positive whole number, the sum of these observations always has to be a whole number. For these variables to test for fraud: calculate ( M ) multiplied by ( n ). This calculates the Sum which MUST be a positive whole number. If the calculated Sum isn't a positive whole number; the reported mean ( M ) is mathematically impossible - thus the researcher either cooked the data or made a mistake. A recent study of 260 research papers published in highly reputable psychological journals found that 1 in 2 of these research papers reported at least one impossible value , and 1 in 5 of these research papers reported multiple impossible values. When the authors of the 21 worst offending research papers were asked for their raw data (so that its reliability could be checked) - 57% angrily refused. Yet such release of raw data to other researchers is required by most scientific journals. (Here is an example of a research paper filled with mathematically impossible means.)

        • If the SD is mathematically impossible (online calculator): When researchers fraudulently "cook" their data, they may accidently give their data a mean and standard deviation that is mathematically impossible.

        • If the SD/M is very small (i.e., the variable's standard deviation is very small compared to the mean suggesting data smoothing).

        • If the SD's are almost identical (i.e., the variables have different means but almost identical standard deviations).

        • If the 4th digit of the values of the variables aren't uniformly distributed - since each should occur 10% of the time (Benford's Law).

        • If the researcher is legally prevented from publishing negative findings about a drug or therapy because that would violate the "nondisclosure of trade secrets" clause in the research contract (i.e., it is a "trade secret" that the drug or therapy is ineffective - hence this can not be "disclosed"). Approximately half of all registered clinical trials fail to publish their results.

        • If the researcher refuses to release his raw data to fellow researchers (so that they can check its validity). In order to be published in most scientific journals, a researcher must promise to share his raw data with fellow researchers. Thus a researcher's refusal to do so is almost a sure indicator of fraud.

        • If the research study's data contradicts the study's own conclusions - surprisingly, this often occurs.

    • Calling Bullshit In The Age of Big Data - "Bullshit is language, statistical figures, data graphics, and other forms of presentation intended to persuade by impressing and overwhelming a reader or listener, with a blatant disregard for truth and logical coherence." Reading the syllabus of this university course should be required reading for every student of mental health. This syllabus is absolutely fantastic!

    • Statistical Methods in Psychology Journals: Guidelines and Explanations - American Psychologist 1999

    • Not All Scientific Studies Are Created Equal - video

    • The efficacy of psychological, educational, and behavioral treatment

    • Estimating the reproducibility of psychological science

    • Psychologists grapple with validity of research

    • Industry sponsorship and research outcome (Review) - Cochrane Library

    • 'We've been deceived': Many clinical trial results are never published - (text and video)

    • Junk science misleading doctors and researchers

    • Junk science under spotlight after controversial firm buys Canadian journals

    • Medicine with a side of mysticism: Top hospitals promote unproven therapies - Are some doctors becoming modern witchdoctors?

    • When Evidence Says No, But Doctors Say Yes

    • Cochrane Reviews (the best evidence-based, standardized reviews available)

    Research Topics

    Back to top

    Internet Mental Health © 1995-2019 Phillip W. Long, M.D.