Introduction
This document gives a historical record of the changes made to the dataset since its initial release. It will also contain, if applicable, a list of known errata that will be updated in the next release of the dataset. We encourage scholars using the data to always use the latest version available if possible.
Changes from Version 23.1 to 24.1
Dyad-years added

Dyads removed

Misc. Changes

Changes from Version 22.1 to 23.1 New dyads added
Dyad-years added

Dyads removed

Misc. Changes
Changes from Version 21.1 to 22.1
New dyads added
Dyad-years added

Dyad-years removed

Misc. Changes

New dyads added

Dyad-years added

Dyad-years removed

Misc. Changes

Changes from Version 19.1 to 20.1
New dyads added

Dyad-years added

Dyad-years removed

Changes from Version 18.1 to 19.1
New dyads added

Dyad-years added

Dyads removed

UCDP Dyadic Dataset Version History and Known Errata, Version 24.1
Changes from Version 17.2 to 18.1
New dyads added

Dyad-years added

Misc. Changes Dyads

New dyads added

Dyad-years added

Dyads removed

Misc. Changes Dyads

Changes from Version 1-2016 to 17.1
The ID system was changed in version 17.1. To download a conversion table containing new and old IDs, visit http://ucdp.uu.se/downloads/.
New dyads added

Dyad-years added

Dyad-years removed

Misc. changes

Changes from Version 1-2015 to 1-2016

New dyads added
Dyad-years added

Dyads removed

Misc. changes

Erata
The actor NDFB-S, active in dyad 14102 in conflict 1-227 was given an incorrect actor ID in version 1-2015, 5826. The correct actor ID should be 3151.
New dyads added Dyad-years added
Dyad-years removed
Misc. changes
UCDP Dyadic Dataset Version History and Known Errata, Version 24.1
New dyads added
Dyad-years added
Dyads removed
Dyad-years removed
Misc. changes

Erata
In version 1-2013, the dyad Government of Pakistan – BLF was given a dyad id of 840 for the year 2012. However, the id was not accurate. The correct dyad id for this dyad is 544.
Change in ConflictID
UCDP codes three different categories of organized violence and there has been a problem of mix-ups with regards to conflict id:s. Thus, in order to prevent confusion, the UCDP/PRIO Armed Conflict Dataset (which focuses on state-based conflicts) has conflicts a ‘1’ and  a  dash  before  the  id.  Non-state introduced (http://www.pcr.uu.se/research/ucdp/datasets/ucdp_non-state_conflict_dataset_/) have a ‘2’ and a dash before the id.
Name change for states
All entries for Vietnam have been changed to Vietnam (North Vietnam). - All entries for North Yemen have been changed to Yemen (North Yemen). -
Slightly revised format for startdates
As the UCDP event coding and georeferencing process has progressed, more precise information on conflict events have been found and systematised. To provide the user with as precise information as possible, some changes have thus been made to the format in which startdates are reported. For more information on this, see the codebook at http://www.pcr.uu.se/research/ucdp/datasets/ucdp_dyadic_dataset/. Aside from the above-mentioned change in start date format, the new and improved core data has also made it possible to provide additional information on the start of a new phase of conflict activity. From v1-2014, a new startdate2 is provided as soon as there has been at least one year of inactivity in the conflict. The '1' previously used to indicate when startdate2 is in a different year than startdate has been removed. Changes from Version 1-2012 to 1-2013 New dyads added
Dyad-years added

Dyad-years removed

Misc. changes

Changes from Version 1-2011 to 1-2012
Mistake in previous version history
A new dyadid was reported for the dyad Government of Niger – UFRA. However, the id was not accurate. The correct dyadid for this dyad should be 762.
Change of dyadID

New dyads added

Dyad-years added

Dyads removed

Dyad-years removed

Misc. changes

New format for startdates
In order to streamline UCDP's data outputs with regard to the format for writing startdates, this has been altered in version 1-2012 of the dataset. In previous versions, a startprecision of 3 (meaning that day is unknown; month and year are precisely coded) or 4 (month is assigned; year is coded precisely) meant that the day was set to the first of that month. In this version, however, this has been changed to the last of the given month. Furthermore, while in previous versions a startprecision of 5 (day and month are unknown, year is coded precisely), 6 (year is assigned) or 7 (year of first death is missing) meant that the date was set to 1 January, this has now been changed to 31 December. Changes from Version 1-2010 to 1-2011 Dyads removed
New dyads added

Dyad-years added

Misc. changes
Dyad-years removed

Change of DyadID

New variable included
Version 4-2011 of the dataset includes a new variable: SideBID. SideBID is the unique identifier of the actor on side B in the conflict. For government actors, the Gleditsch & Ward (2007) country codes are used. For non-state actors, the ID is taken from the UCDP Actor Dataset (http://www.pcr.uu.se/research/ucdp/datasets/).
Dyads removed
Dyad-years removed
New dyads added
Dyad-years added
Misc. changes
UCDP Dyadic Dataset Version History and Known Errata, Version 24.1

A note on some name changes
In version 1-2010, an effort has been made to streamline the names of the states included. Furthermore, UCDP has continued the effort to include easily understood and commonly known names, wherefore for instance the name North Korea is used instead of People's Republic of Korea. In previous versions this has not been done full out, but in version 1-2010 we have tried to make all the necessary changes. It should subsequently be noted that while all state actors in the dataset are given Gleditsch and Ward numbers, there are a number of instances where we differ from Gleditsch and Ward when it comes to the names of the states. The following changes have been made:
Changes from version 1.0 to version 1-2009
Misc. changes

Two notes on name changes
In a continued effort to streamline the way that we write names in our datasets and databases, UCDP has applied a new rule when dealing with splinter groups. If a group splinters and it is clear which group is the faction as they take a somewhat new name (e.g. Palipehutu–FNL in Burundi, splitting from the original Palipehutu) the name is written with a long hyphen without any spaces. If, on the other hand, the splinter does not take a new name, but maintains that they are the original group (for coding rules regarding how we determine grouping is the faction, see the UCDP Dyadic Dataset codebook which at http://www.pcr.uu.se/research/UCDP/data_and_publications/datasets.htm) UCDP needs to create a name in order to be able to separate the factions in the data. The faction is then given the original name, followed by a space, a long hyphen, a space and then the initials of the leader of the group. An example is the faction of FRUD that kept on fighting in Djibouti when the main part of the group had signed a peace agreement. The faction's leader was called Ahmed Dini, and the name of the group was subsequently set as FRUD – AD. In Version 4-2009, another change is that we have chosen to use the same name for a group for all years of the conflict, even if it has in fact changed names during the conflict period. Thus, instead of recording PRA (Popular Resistance Army) for Uganda 1982, we have recorded NRA (National Resistance Army) for all years (1982-86), even though the group only changed its name from PRA to NRA in 1983. In earlier versions the name history could be seen in the name (e.g. PRA/NRA and UDCA/LRA). This is thus not the case in version 4- 2009. However, a special rebel group dataset will be released in July where the name history of all groups registered in UCDP data will be included. The dataset will be available at http://www.pcr.uu.se/research/UCDP/data_and_publications/datasets.htm .