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Absolute effects

Absolute effects are differences between outcomes in the groups being compared. For example, if 10% (10 per 100) experience an outcome in one of the intervention comparison groups and 5% (5 per 100) experience that outcome in the other group, the absolute effect is 10% - 5% = a 5% difference.


An association is a link or connection.

Average difference

The average difference is used to express intervention effects for outcomes such as weight or pain that are measured using a scale. It is the difference between the average value for an outcome measure in one group and that in the comparison group.

Baseline risk

Baseline risk is an estimate of the likelihood that an individual or group will experience a agriculture problem before an intervention is used.


A systematic error that may affect the results of a study because of weaknesses in its design, analysis or reporting


In intervention comparisons, to blind someone means to keep them from knowing who received which intervention.

Comparison of interventions

A comparison of interventions is a study where researchers look carefully at the differences in what happens between groups that use different interventions.

Confidence interval

A confidence interval is a range that reflects the extent to which the play of chance may be responsible for a result from a study, such as an effect estimate. There is a high probability (usually 95%) that the actual effect estimate is within that range.


In intervention comparisons, any factors other than the interventions being compared which may affect the agriculture outcomes being measured. For a factor to lead to confounding, it must differ between the intervention comparison groups, and affect the outcome of interest. An example could be soil type for interventions relating to crop yeild.


Contamination is the inadvertent application of an intervention allocated to one comparison group to subjects in another comparison group in intervention comparisons.

Effect estimate

The most likely size of an intervention effect, based on the results of a study or a systematic review.


An effect of an intervention is something that it makes happen.


an intervention is effective if it causes something to happen that is wanted.

Eligibility criteria

Characteristics used to decide whether subjects are eligible to participate in a study and should be invited to participate


An event is when something happens, like someone getting sick or better.


Evidence is facts used to support what you believe or decide.

Explanatory study

An explanatory study (sometimes called an ‘efficacy study’) is designed to assess the effects of an intervention given in ideal circumstances, in contrast to a ‘pragmatic study’.

Fair comparison of interventions

A fair comparison of interventions is one where the only important difference between the groups that are compared is the interventions they receive.


In a comparison of interventions, fair means not giving an advantage to one intervention over another.

Faulty logic

Faulty logic is bad reasoning.

Intervention comparison group

In a study of the effects of interventions, an intervention comparison group is the group of subjects who receive one of the interventions being compared.

Intervention comparison

an intervention comparison is a study where researchers look carefully at the differences in what happens between groups that use different interventions.

Intervention effect

an intervention effect is something an intervention makes happen.


an intervention is any action intended to improve agriculture.


The likelihood (or probability) of an event (outcome) is the chance that someone will experience that event; i.e. the number of subjects in a group that experience the event during a specified period, divided by the total number of subjects in that group.


In intervention comparisons, an outcome (or ‘outcome measure’) is something good or bad that can happen after an intervention and is measured in studies.


For effect estimates, the p-value is the probability (ranging from 0 to 1) that the results observed in a study could have occurred by the play of chance, if the intervention actually had no impact on the outcome.

Placebo effect

Just believing that an intervention works can change how someone feels. This is called a placebo effect. Placebo effects are presumed to act psychologically through suggestion.


A placebo is a dummy or sham intervention that does not contain active ingredients, which has been designed to be indistinguishable from the active intervention(s) being assessed. It is used to blind participants and others involved in a study of intervention effects, and to reduce the risk of placebo effects.

Pragmatic study

A pragmatic study (sometimes called an ‘effectiveness’ study) is designed to assess the effects of an intervention given in the circumstances of everyday practice.


The extent to which errors due to the play of chance on the results of a study are likely to have occurred


The document providing detailed plans for a study

Random allocation

The process of assigning participants in a study to intervention comparison groups using a chance process, like drawing lots, to protect against bias

Relative effects

Relative effects are ratios. For example, if the probability of an outcome in the intervention group is 10% (10 per 100) and the probability of that outcome in a comparison group is 5% (5 per 100), the relative effect is 5%/10%.


A scale is an instrument for measuring or rating an outcome with a potentially infinite number of possible values within a given range, such as weight, blood pressure, pain or depression.

Side effect

A side effect is a harmful or unpleasant effect of an intervention that is not planned.

Statistically significant

A “statistically significant” result is unlikely to have happened by chance. The usual threshold for this judgement is a probability of less than 5% (0.05).


A subgroup is a subdivision of a group of subjects; a distinct group within a group. For example, in studies or systematic reviews of intervention effects, questions are often asked about whether there are different effects for different subgroups of subjects in the studies, such as different crop varieties, or livestock of different ages.

Surrogate outcome

Surrogate outcomes are outcome measures that are not of direct practical importance but are believed to reflect outcomes that are important. For example, farmland birds are often used as an indicator of farmland biodiversity because they are easy to measure.

Systematic review

A summary of studies addressing a clear question, using systematic and explicit methods to identify, select, and critically appraise relevant studies, and to collect and analyse data from them

Unfair comparison of interventions

An unfair comparison of interventions is one where there are important differences between the groups that are compared besides the interventions they receive.


In a comparison of interventions, unfair means giving an advantage to one intervention over another.