# Free interval based on a dependent variable

Background

This topic contains details about defining a Free interval. For the main procedure, see Free interval.

note Dependent variable here also includes external data and manually-scored behaviors, not behaviors of Rat and Mouse Behavior Recognition.

To specify the dependent variable

In the Free Interval window, under Start criterion or Stop criterion, choose Dependent variable.

1.In the Start at / Stop at field, enter the time of the start (or stop) of the interval relative to the event described by the variable.

example 1 To start an interval 1 s before the animal enters a zone, next to Start at enter 0:00:01:000 before event.

example 2 To stop an interval 10 s after the total distance moved reached 10 m, next to Stop at enter 0:00:10:000 after event.

2.From the Select variable list, choose the dependent variable.

For example In zone if you want the interval to start or stop when the animal enters a zone for the nth time, or has spent a specific time in that zone.

3.From the Statistic list, choose the statistic of the dependent variable. For example:

▪Frequency if you want the interval to start/stop when the animal has entered a zone for the 10th time,

▪Cumulative Duration if you want the interval to start/stop when the animal has spent a specific total time in that zone.

See Statistic: When to use Frequency, Current, or others

4.Click the Settings button to specify the dependent variable more in detail.

For example, which zone the animal should enter to define the stop of the interval, or which body points should be in the zone. See Dependent Variables in Detail

5.Next to is:, specify which value the statistic should have to define the start/stop of the interval, using the operators available (<=, >= or false/true).

Return to To specify a Free interval

Notes

▪The following dependent variables are not available as start/stop criteria: Activity state, Acceleration state, and the behaviors of Rat or Mouse Behavior Recognition.

▪A Free interval can only start at the time that, or before (not after) a variable reaches the specified value. Similarly, a Free interval can only end at the time that, or after (not before) a variable reaches the specified value.

▪If you have imported external data in an experiment, you can define an interval based on the values of the resampled external data, not the original (imported) external data. Choose the external data from the Select variable list.

See External data (resampled) and Examples of Free intervals in the Analysis profile

▪If you want to define a free interval based on two values of external data, for example Heart rate between 300 and 400 bpm) then do not use Free intervals. Instead, use the dependent variable under External data in the Analysis profile.

Statistic: When to use Frequency, Current, or others

▪Frequency. To define an interval that starts/stops when the animal has entered a zone or has shown certain behavior (Moving, Highly mobile, Grooming, etc.) a number of times.

▪Current. To define an interval that starts/stops when a variable reaches a specific value. For discrete variables (state events or point events) like In zone, the Current statistic can be false or true.

examples

▪For In zone, Current= true means that the interval starts/stop as soon as the animal enters the selected zone. Current= false means that the interval starts/stops as soon as the animal is outside the selected zone.

▪For Velocity, Current >= 10 means that the interval starts/stops as soon as the animal’s velocity is higher then or equal to 10.

▪Total. This is used especially with Distance moved. This makes the interval starts/end when the animal has covered a specific distance since the start of the track or the start of the interval.

▪Cumulative Duration. To define an interval that starts/stops when the animal has been in a certain state (that is, within a specific zone, or in the state Highly mobile, etc.) for a specific total time since the start of the track or the start of the interval. It does not matter if the subject’s state was sometimes interrupted.

example The interval starts when Cumulative duration of In zone >= 10 s. The green dot indicates where the interval starts.

▪Current Duration. To define an interval that starts/stop when the animal has been in a certain state (within a specific zone, or in the state Moving, etc.) for a specific time without interruption.

example The interval starts when Current duration of In zone = 10 s. The green dot indicates where the interval starts.

▪Latency to first. To define an interval that starts/stops when the time to the first instance of an event (for example, the animal being in a certain state or within a zone) has reached a specific value. Note that latency is always calculated from the start of the track.

How dependent variables are calculated to find the stop of an interval

Where in the track an interval ends depends on the value of the statistic of the dependent variable used. The following information applies to the statistics Total, Frequency, Current Duration, Cumulative Duration, and Latency to first.

Once the start point of an interval is found, EthoVision XT resets the statistic at that point, and starting from the next sample time, updates its value until it matches the stop criterion.

▪If the stop criterion is met, the interval is fully defined.

▪If the value of the statistic does not match the stop criterion before the end of the track, the result depends on whether you select the option Ignore last interval if incomplete. See Free interval

example 1 The statistic Frequency for the dependent variable In Zone. A free interval is defined that ends when the Frequency of In zone is equal to 2. In the figure below, the green bars represent the time when the subject is in the specified zone (numbers indicate frequency). The green dots indicate when the Start criterion is met (for sake of simplicity, it can be any criterion). The arrows represent the free intervals defined. The red circles show when the statistic Frequency for In zone is reset to zero.

example 2 The statistic Total for the dependent variable Distance moved. A recurring free interval is defined to split the track in segments of 100-inch distance moved.

▪Interval start: Dependent variable Distance moved, Statistic Total >= 0.

▪Interval stop: Dependent variable Distance moved, Statistic Total >= 100.

When the second, third, etc. interval starts, the total Distance moved is reset to zero (see the red circles) and updated, starting from the next sample time, until the Stop criterion is met.

Other statistics

For other statistics like Current (for example In zone or Not in zone) EthoVision XT evaluates the value at the current sample, and checks that the Stop criterion is met.