Knowledge Base

Aim

Trial Statistics give you summary statistics of individual trials. If a trial includes two or more tracks (subjects), the statistics are by default shown for each subject separately.

The Data profile filters tracks and/or intervals within tracks. If the Data profile contains groups of tracks, these groups are ignored in the results. To view results per group, choose Results > Group Statistics and Charts.

Cumulative Duration

The cumulative duration of the state variable in the whole track, or in the track segment selected. For example, the time that the animal spent in a zone (for the variable In zone), or the time that the subject was in the state Mobile.

When a state does not occur at all in a track or track segment, the value of Cumulative Duration is zero.

Cumulative Duration (%)

The Cumulative Duration divided by:

• If you do not define time bins: The duration of the track (this corresponds to the Recording duration independent variable, not Trial duration). This is also the case when you define nesting intervals or results per zone.
• If you define time bins: The duration of a time bin defined.

This statistic is expressed as a percentage.

Cumulative Duration within Nesting (%)

The Cumulative Duration divided by:

• If you calculate results per zone: The total time the animal is in the zone.
• If you defined track segments with Nesting: The total duration of the track segments defined.
• If you defined time bins: The duration of a time bin defined.
• If you combine any of the three above: The duration of the time period shared by all selection criteria (the time periods of each criterion are combined with AND logic).

This statistic is expressed as a percentage.

Frequency

The total number of occurrences of a state (only for state variables).

Latency to First

The time from the start of the track to the first occurrence of the behavior (for example, the first time in the track that the animal is in a zone). Latency is always calculated from the start of the track, even when you define time bins and nesting intervals.

Latency to Last

The time from the start of the track to the last occurrence of the behavior. Latency is always calculated from the start of the track, even when you define time bins and nesting intervals.

Notes about Latency to First/Last

• Latency to First and Latency to Last are calculated from the start of the track. This is the time when EthoVision XT collects the first sample (missing or not). If the animal is not yet in the arena and tracking has started, EthoVision XT collects a number of missing samples. The time that the animal is missing is included in Latency to First/Last. This overestimates the "true" latency, which should be calculated from the time that the animal is released. To prevent this from occurring, make sure that the Trial Control rule includes a Start track condition in such a way that tracking only starts when the animal is first found in the arena.
• To calculate the time from an event to another event in the trial, select a Free interval in the Analysis profile.
• When two or more animals are tested simultaneously in the same arena, the meaning of Latency to First/Last depends on how you set the start condition. Suppose you start your trial by releasing one animal, then a little later the second animal, and you want to calculate the Latency of In Zone A for both subjects. Consider the two scenarios:
  • If you set the Trial Control to start tracking when any subject is found in the arena, tracking starts when the first animal is released. Latency is calculated from that point also for the second animal, which enters the arena later. This means that Latency for this animal will be overestimated.
  • If you set the Trial Control to start tracking when all subjects are found in the arena, tracking starts when both animals are found — that is, when the second animal is released and the first is detected (also when in a hidden zone). Latency is calculated from this point, so Latency for the second animal is correct. However, for the first-released animal, the time that it was in the arena before the second was released is not counted in Latency. This means that Latency may be underestimated, for example when the first animal enters Zone A before the second animal is released. For this reason, try to release the animals at the same time, or one immediately after the other.

Mean

• For linear variables like Distance moved, Velocity, Distance to zone, or Distance between subjects, and the variables Turn angle, Angular Velocity, and Meander, the arithmetic mean is used — that is, the sum of the per-sample values divided by the number of samples.
• For the angular variables Heading, Head direction, and Heading to Point, the mean is calculated according to the circular mean formula, where α is the per-sample angle and N is the number of samples. The circular mean value can also be represented by the angle of the vector resultant R obtained by summing up all the vectors that represent the per-sample angle values.
• For state variables like In zone, Movement, and the behaviors scored manually or automatically recognized: the sum of the duration of occurrences of the state, divided by the number of occurrences.

Minimum

The lowest value of the variable.

Note: For state variables, this is the minimum duration of the instances of a state, for example Moving. When the state does not occur at all in a track or track segment, the value of Minimum is zero.

Maximum

The highest value of the variable.

Note: For state variables, this is the maximum duration of the instances of a state, for example Moving. When the state does not occur at all in a track or track segment, the value of Maximum is zero.

Number of Samples

The total number of valid values of that variable (only for numerical variables like Distance moved).

Standard Error

The standard deviation divided by the square root of the number of samples. This is also the case for angular variables Heading, Head direction, and Heading to Point.

Standard Deviation

For most variables, including Turn angle, Angular Velocity, and Meander, the sample standard deviation of the mean is used, where x is the individual variable value and x̄ is the mean of the variable. N is defined as follows:

• For numerical variables like Distance moved or Velocity: the number of samples used to calculate the mean.
• For state variables like In zone, Mobility, and the behaviors scored manually or automatically recognized: the number of occurrences of the state used to calculate the mean (for example, when a subject visited a zone 4 times, then N=4).

For the angular variables Heading, Head direction, and Heading to Point, the circular standard deviation is used, where R is the resultant vector length (see the circular mean description above) and N is the number of samples.

Total

The sum of all the values.

Source: EthoVision XT 19 Help, Noldus Information Technology