Balanced panel vs unbalanced panel. Data data and shp files Reproducible ex.

Balanced panel vs unbalanced panel However, once I start my regression I get an unbalanced panel and the n decli Jan 12, 2014 · The data step solution, which is nearly identical to the SQL in its functionality: data have; input person year; datalines; 1 2008 1 2009 1 2010 2 2008 2 2010 3 2008 3 2009 3 2010 ; run; data want; do _n_ = 1 by 1 until (last. With balanced data (12 clubs) my data suffers from sample selection bias. the impact of different regressors are roughly the same for balanced but not for unbalanced Mar 2, 2018 · Balanced: you observe yearly earnings for all three, in each year Unbalanced: you only observe John's earnings from 1993 onwards, and Tim's until 1998. Balanced panel data means that each unit is observed every time period such that: \[n=N \times T\] where \(n\) is the total number of observations, \(N\) is the number of units, and \(T\) is the number of time periods. 2. What is balanced construction exactly? Let’s take a look at the components that make up a laminate panel: The core of a laminate panel is typically a particleboard, plywood, or MDF substrate. This includes panels with randomly and non-randomly missing observations. ) und alle Zeitpunkte Informationen vorhanden. The Chamberlain projection approach for the balanced-panel case is reviewed. therefore, the question arises: In case of correlation of these pattern with the idiosyncratic errors, which is best to avoid biased estimtators? was shown to be equivalent to the Within estimator for balanced panels in Chap. See also Wooldridge (2010) and Abrevaya (2013). These connections form the backbone of audio signal transmission, impacting everything from professional recording… May 25, 2021 · I have a problem with my panel data regression. Firm_id is a firm’s identification number, branch_id is each branch’s identification number. Why? We can always extract balanced panel data sets from the full one; we can't go the other way around. May 14, 2021 · When the first panel was created it showed (unbalanced with 140 gaps). Should I convert the unbalanced panel to balanced with the observations for those missing state-year set to 0? `xsmle` is a new user-written command for spatial analysis. `xsmle` allows users to handle unbalanced panels using its full compatibility with the `mi suite` of commands, use spatial weight matrices in the form of both Stata matrices and `spmat` objects Jun 25, 2016 · panel variable: ID (unbalanced) time variable: YEAR, 2000 to 2015 delta: 1 unit How can it be that my panel data is unbalanced when every firm has the same number of observations (16) with the same IDs and the same years (2000-2015)? I really appreciate any help! Best wishes Florian Balanced vs. , year, month, etc. Certain panel data models are only valid for balanced datasets. missing values. Nov 22, 2018 · Here's a slight modification of Ben's answer. Unbalanced Panels: • Balanced Panels: foreach uniti therearethesame number of(T)observations, i. e. Then there’s panel data that’s both balanced and unbalanced. Usually I use the data is balanced, and I am confused about their difference. Jun 8, 2024 · The distinction between balanced and unbalanced panel data is crucial in econometric analyses and research. Diese sind vor allem dann gefährlich, wenn Beobachtungen nicht zufällig fehlen (selection bias). We consider the quasi–maximum likelihood estimation of a wide set of both fixed- and random-effects spatial models for balanced panel data. fehlende Werte. It does not check whether any of the other variables in the data set contain missing values, which constitutes an unbalanced panel in the econometric sense. , that the units Mar 16, 2014 · We explore the effect of balancing unbalanced panel data when estimating primal productivity indices using non-parametric frontier estimators. 详细资料见附件“Unbalanced Panel Data Models” Panel Data: Fixed and Random E ects 1 Introduction In panel data, individuals (persons, rms, cities, ) are observed at several points in time (days, years, before and after treatment, ). However, I know for a fact that the dependent variable in those years for those states is 0. cases to find rows that have no NA in them. For unbalanced panels I redefine the J matrices to be blockdiagonal of size H×H, corresponding in structure to the groups or subgroups they represent. Oct 26, 2016 · Download Citation | Unbalanced panel data: Methods and Applications | Panel data is a data type increasingly used in research in economics, social sciences, and medicine. person); set have; by person; if yearcount=3 then output Nov 7, 2019 · Observations are at the state-year unit of analysis. The primary types are balanced panels and unbalanced panels. Ada panel data yang balance dan ada juga yang tidak balance alias unbalance. Because you will experience the difference of a balanced vs. The fact that you panel is unbalanced should not be ignored, even if it is not problematic. g. A balanced panel is ideal but this is not always the case because of missing values, however most panel data regression models can be used for unbalanced datasets. Whenever you're trying to create a balanced panel, I find it easiest to just use stack/unstack, rather than re-define the index: Oct 1, 2006 · This paper surveys the econometrics literature on unbalanced panels, including panels with randomly and non-randomly missing observations and panels with special features including pseudo panels, rotating panels and censored panels. Hi Frances. Unbalanced Panel In a balanced panel, the number of time periods T is the same for all individuals i. ) in every time period (e. Unbalanced Panels This is an unbalanced panel with 7,293 individuals. an unbalanced panel contains missing observations for at least one time period or one entity. Furthermore, we link this Balanced and Unbalanced Panels • Distinction: Balanced vs. One of the key advantages of panel data is its ability to control for unobserved heterogeneity. In fact, Cameron and Trivedi (2010) provide sample code to conduct the robust Hausman test with a balanced panel and Question: The difference between an unbalanced and a balanced panel is that Group of answer choices you cannot have both fixed time effects and fixed entity effects regressions. Unbalanced panel datasets have missing values at some time observations for some of the groups. One common question among audiophiles and music enthusiasts is whether to use balanced or unbalanced audio connections. the first data. Most introductory texts restrict themselves to balanced panels, despite the fact, that unbalanced panels are the norm. Likely you mean tidyr::fill() - I do not think it is aware of the special pdata. The original data structure is as follows: Oct 1, 2004 · The purpose of this paper is to integrate, for random effects situations, the regression system ML approach to balanced panel data with the single equation approach to unbalanced panel data, when the attrition or accretion is random. Lantas apa perbedaannya? Balanced Panel Data memiliki jumlah pengamatan yang sama untuk semua kelompok. Apr 25, 2017 · To conclude, the dillemma as I see it is should one "stick" to a weakly unbalanced panel data sample or should one try to produce imputed outcomes in order to create a strongly balanced panel? Thus, does it "worth taking the risk" to fill in missing data in favor of having to deal with a strongly balanced panel? When I use stata to set a panel data, but it is reported that the data is an unbalanced panel data. Short panel: many individuals and few time periods. This paper keeps the derivations simple and easily tractable, using the Fuller and Battese (1974) transformation extended from the balanced to the unbalanced panel data case. In ad- dition, we survey panels with special features including pseudo panels, rotating panels and censored panels. An unbalanced panel is a dataset with missing observations for one or more entities over various periods. County 1001 is showing up for every year since 2000-2020. Sep 7, 2016 · Yes, you are right. Therefore, for county like 1011 and 1027 I need to fill in the wanted variable as 0 when the county is not showing up for a number of years. After getting the balanced panel, I want to do a panel regression at the firm level. With a balanced panel, T i = T 8i, which requires fewer steps to conduct the robust Hausman test in Stata. Otherwise we are dealing with an unbalanced panel. Die Paneldatenanalyse ermöglicht es uns, individuelle Heterogenität zu untersuchen und ermöglicht uns die Kontrolle über beobachtbare Variablen, die sich im Laufe der Zeit ändern. 6 (especially pandas) to solve this. Example for a balanced panel: The Mikrozensus in Austria is a household, hh, survey, with the same size of 22. For In contrast, unbalanced panel data occurs when some subjects have missing observations at certain time points, which can complicate the analysis. One primary feature is the variability in the number of observations for each entity. Mar 7, 2014 · I have two data. Apr 1, 2001 · For balanced panels it was possible to neatly stack the J matrices of all ‘1's using I⊗J products. Incomplete panels are more likely to be the norm in typical economic empirical settings. Long panel: many time periods and few individuals Download Table | Balanced and Unbalanced Panel from publication: Panel Data Analysis with Stata Part 1: Fixed Effects and Random Effects Models | The present work is a part of a larger study on Before moving further, we need to check if our panel data is properly balanced. The unbalance may follow from the sampling process, which often involves endogenous variables, violates ‘classical’ assumptions in regression analysis and makes the observations distorted by the data generating process. from publication: Unified knowledge based economy hybrid forecasting | Many synthetic composite indicators have been developed with Meaning, does a high draw of 11 amps/3 amps cost my wallet more than say 7 amps and 7 amps balanced between the hots? Does the utility company see total an increased draw on their side if I'm unbalanced? I only ask because my new panel was installed recently, and I'm always seeing super high loads comparatively on one side but not the other. B. Es wird zwischen einem „Balanced“ Panel und einem „Unbalanced“ Panel unterschieden. Assume correlation (clustering) over time for a given individual, with independence over individuals. Unbalanced panel data is more likely to occur in economic data collection. Unbalanced Panel Data memiliki nilai yang hilang pada beberapa pengamatan waktu untuk beberapa grup. Unbalanced panel data can be messy. I red a book that notes unbalanced panel data has to be checked for whether it is completely randomly or not before we run any analysis. Panel data can be structured in a balanced or unbalanced manner, depending on whether all entities are observed for the same time periods. So the first question that appears is: How can I check pooled OLS vs Fixed Effects? Additionally, my panel is unbalanced: firms in my panel might get bankrupt or merge with other companies. , balancing 2-years by 2years). Gaps: you observe Barbara's earnings from 1990-1993 and 1995-1999. Each entity is observed repeatedly, allowing for the analysis of both cross-sectional and time series variations. Each hh has to record its consumption expenditures for 5 quarters. Unbalanced Panel Data Models Unbalanced Panels with Stata Balanced vs. Keuntungan dengan menggunakan data panel dalam pemodelan regresi Paneldaten mit fehlenden Werten werden als "unbalanced Panel" bezeichnet, während Paneldaten ohne fehlende Werte als "Balanced Panel" bezeichnet werden. A balanced panel dataset ensures each panel member or entity is observed for the same time periods. , cases where the individuals are observed over the entire sample period. Its primary Feb 8, 2023 · One way to balance a panel is to remove individuals with incomplete data, another way is to fill in a value, such as NA or 0 for the missing observations. The equivalence between various estimators for the balanced-panel case is also reviewed. Modified 10 years, 5 months ago. Conversely, any approach aimed at discarding missing data and creating a balanced panle from an unbalanced one, ends up making-up your original sample and biasing your analysis (especially if the missingness is informative). Balanced vs. The data structure is complete with no missing observations. frame structure and it might destroy what you achieved; check its documentation (I ha Mar 25, 2020 · Some may ask: What are properly balanced panel data? Generally, a properly balanced panel means that all possible ID variables and have data for the same (or appropriate) time period. For the first approach, you can use complete. Bei einem Unbalanced Panel liegen I would construct and maintain only the full (unbalanced) data set with many variables with many missing values. , impute) on the missing values. Following Amemiya (1971), the Within residuals u for the unbalanced panel are Download Table | Balanced and unbalanced sample panel data set. In a balanced panel, all panel members (cross-sectional data) have measurements in all periods, or each panel member is observed every year. Jan 27, 2025 · Clarity and quality of sound can be significantly influenced by the type of connection used—balanced or unbalanced. I have an unbalanced panel dataset because some respondents dropped out from the survey (since time series, high probability of getting this issue). , the second dataset above) is a dataset in which at least one panel member is not observed every period. Panel data can be balanced or unbalanced. Then, we discuss some intermediate solutions (e. . frame looks like this: date1 &lt Dec 22, 2016 · In focus are observation (selection) rules and systematically unbalanced panel data. K includes panels with randomly and non-randomly missing observations. This means you do not have a balanced panel for that particular variable. A balanced panel dataset contains observations for all entities across all time periods, ensuring uniformity in the data structure. I am primarily using categorical variables like whether the individual is self employed or not, part vs full time etc. . First, we list a series of pseudo-solutions aimed at making an unbalanced panel balanced. that in case of unbalanced panels, deviating OLS and FE estimates should be considered as evidence that non‐response is not ignorable for the differences-in-differences estimation. Fixed Effects vs. • Unbalanced Panels: The number of observations varies, e. Feb 24, 2020 · You can use the usual data frame insert methods (in conjunction with subsetting) of base R. Study with Quizlet and memorize flashcards containing terms like The difference between an unbalanced and a balanced panel is that, The main advantage of using panel data over cross sectional data is that, Consider the "before and after" panel regression. Balanced panel Unbalanced panel abstract We explore the effect of balancing unbalanced panel data when estimating primal productivity indices using non-parametric frontier estimators. Apakah panel itu harus selalu balance? Ternyata tidak juga. Nov 29, 2019 · Balanced panel datasets have the same number of observations for all groups. , balancing 2-years by Unbalanced panels exhibit several key characteristics that differentiate them from balanced panels. As a preliminary to the ML problem, the generalized least-squares (GLS) problem is considered. An unbalanced panel is a dataset where entities are observed a different number of times. 经管之家是国内活跃的经济、管理、金融、统计论坛，提供丰富的专业知识和交流平台。 Balanced vs. ) heterogeneity. fill() is not from base R, not from plm. " Jan 21, 2020 · I would go unbalanced (by the way, Stata can handle both balanced and unbalanced panel datasets with no problems). Tidak ada data panel yang secara umum lebih baik daripada data panel yang lain. However, I am curious about the entit Sep 6, 2014 · From Unbalanced to Balanced Panel. Sedangkan jika jumlah pengamatan waktu berbeda pada setiap observations. Berdasarkan kelengkapan data panel, terdapat dua jenis data panel yaitu data panel seimbang (balanced panel data) dan data panel tidak seimbang (unbalanced panel data). Unbalance or balanced panel data? With unbalanced data, it suffers from attrition due to relegation of football clubs. In einem BalancedPanel sind für alle Beobachtungseinheiten (Personen, Unternehmen, Regionen usw. Viewed 1k times Feb 12, 2017 · Marcos: xtset calls a panel "strongly balanced" if there is a row in the data set for each panel-time combination in the range of these two identifiers. a total of NT (N times T) observations. This is a balanced panel. with serial correlation of the AR(1) type derived by Baltagi and Li (1992) from balanced panels to unequally spaced panels. ), which reduces the noise introduced by unit (individual, etc. The dataset shows a balanced panel consisting of n= 10, T = 26, N= 260. Jika setiap objek memiliki jumlah pengamatan waktu yang sama maka data panel disebut data panel seimbang. Now the panel shows (Strongly balanced with gaps). Unbalanced Panels: • Balanced Panels: für jede Unit i existieren gleich viele (T) Beobachtungen, d. In an unbalanced panel, there are missing data points for at least one time period or one entity, while a balanced panel has complete data for all time periods and entities. , balancing 2-years by 2 years). person); set have; by person; if year ge 2008 and year le 2010 then yearcount+1; end; do _n_ = 1 by 1 until (last. Dec 21, 2024 · I am conducting a fixed effects model analysis using unbalanced panel data. Jan 4, 2022 · Panel data can be balanced or unbalanced. One method of estimating the panel data regression model with a fixed-effects approach is the within-transformation Abstract: We explore the effect of balancing unbalanced panel data when estimating primal productivity indices using non-parametric frontier estimators. These are particularly dangerous if observations are missing not at random (selection bias). Conversely, an unbalanced panel dataset may have missing observations for certain entities or time periods, which can complicate the analysis but is often more reflective of real-world scenarios. Jika sebaliknya, yakni jumlah unit waktu berbeda untuk setiap individu, maka disebut unbalanced panel. Understanding the differences between these two connection types can help you maximize the performance of your audio system and reduce unwanted noise […] 在一些面板数据中，样本中缺少了某些横截面单位的某些年份数据，我们称数据集为非平衡面板数据（unbalanced panel）。 相应的，如果N个横截面单位中的每一个都有同样的T期数据，则称这样的数据为平衡面板数据。 I am making spatial panel models from the splm library but I cannot make a fixed or random effects model because it comes out that it is an unbalanced panel. A fixed panel is a special case of a balanced panel. There are altogether 27,326 Mar 1, 2014 · Request PDF | Comparing Malmquist and Hicks-Moorsteen productivity indices: Exploring the impact of unbalanced vs. A balanced audio cable features one ground wire and two signal wires, designed to eliminate noise through phase cancellation. May 11, 2019 · Hi! I am using data from the British Household Panel Survey which is an unbalanced panel. In the case of randomly missing data, most Stata commands can be applied to unbalanced panels without causing inconsistency of the estimators. Random Effects Models Mar 16, 2014 · In this contribution, we intend to systematically start exploring the consequences of computing these primal productivity indices using a balanced panel when initially an unbalanced panel data set is available. A balanced panel refers to a dataset where each cross-sectional unit is observed across the same time periods. 500 each quarter. unbalanced construction over time when humidity and temperature in the room change. Mar 16, 2021 · So far we have dealt only with “complete panels” or “balanced panels”, i. I`d like to use python 3. Keywords: Unbalanced ANOVA, Missing Observations, Pseudo Panels, Ro- tating Panels, Censored Panels. It • ‘balanced’ or ‘complete’ panels: –a panel data set where data/observations are available for all cross-sectional units in the entire sample period • ‘unbalanced’ or ‘incomplete’ panels: –a panel data set where some data/observations are missing for some cross-sectional units in the sample period Jul 26, 2018 · I am struggling how to deal with unbalanced panel data. insgesamt NT (N mal T) Beobachtungen. Baca juga : Data panel longitudinal : Apa kelebihanya dan Kekurangannya; Data Wide Vs Data Long : Mana yang Lebih Bagus ? Regresi Data Panel || Balanced Panel dan Unbalanced PanelVidio ini memberikan penjelasan mengenai Regresi Data Panel || Balanced Panel dan Unbalanced Panel. For the case of unbalanced panels (under strict exogeneity), The result is the DiD estimate, and it doesn't rely on a balanced panel in doing so. We require that everyone be present at all times in this situation. I could estimate a DID model on the balanced sample only or simply disregard the fact that panel is unbalanced (I guess it's not a problem for Stata xtdidrgress), but I'm afraid it may create biased results. Der Datensatz ist insoweit vollständig und enthält folglich N × T Datenwerte. Panel data with different time-series observations in each cross-section unit is called unbalanced panel data. *Note my careful use of "average satisfaction" as opposed to "average change in satisfaction" - we are not calculating the store-level changes. Jun 2, 2023 · The main difference between an unbalanced and a balanced panel lies in the presence of missing observations for either a time period or an entity. In addition, we Jan 16, 2022 · In this lecture, balanced and unbalanced panel data is discussed. 7/63 A dataset with an unbalanced panel (e. i for each panel group is the critical di erence between conducting the Hausman test with balanced and unbalanced panels. Oct 1, 2022 · Dear all, I have an unbalanced panel dataset, which means that not all entities have data for all years. balanced panel data | We explore the effect of balancing unbalanced panel data Dec 22, 2016 · Abstract. unbalanced panels • What are they? • When is an unbalanced panel a problem? data missingness that can lead to an unbalanced panel. Types. • Unbalanced Panels: Die Anzahl der Beobachtungen ist unterschiedlich, z. Should I balance the data first, or is it better to proceed with the unbalanced data? What are the trade-offs or implications of each approach? A balanced panel requires that all entities are present in all time periods. , individual, company, person, etc. Downloadable (with restrictions)! We explore the effect of balancing unbalanced panel data when estimating primal productivity indices using non-parametric frontier estimators. Sep 13, 2015 · My question is what data set is the most appropriate to analyze the data. They work also for a pdata. This chapter extends some of the models and procedures discussed in Chapters 2 and 3 to handle unbalanced panel data with unobserved heterogeneit May 28, 2014 · Unbalanced panels are more common in economic fields, if I want to know the behaviour of firms, what will be the differences using unbalanced data panel. Panel Data Feb 27, 2025 · When building or optimizing a high-end audio system, every detail matters—including how your components are connected. So each quarter 4500 members enter/leave the Mikrozensus. In addition, we survey panels with special features including pseudo panels, rotating panels and censored panels. However, if we observed some of the cities in the year 1999 but not all of them, then we would call it an ‘unbalanced panel data set’ (this distinction often May 18, 2016 · In a balanced panel, the number of time periods T is the same for all individuals i . Kind regards, Jordi van Dijk includes panels with randomly and non-randomly missing observations. frame. Are there advantages? Does it depend on analysis's period? Or it will be better use balanced panel? Thanks! Pada Set B, di sisi lain, akan dianggap sebagai panel yang tidak seimbang (unbalanced panel) karena data tidak ada untuk setiap orang setiap tahun. I don't know for sure, but I think none of the unit root tests in Stata can handle unbalanced data at the moment. This handout focuses on panels with relatively few time periods (small T) and many individuals (large N). Pilihan terbaik antara data panel balance dan panel unbalance tergantung pada tujuan dan kondisi yang dihadapi dalam penelitian. This particular panel data set is sometimes referenced as a ‘balanced panel data set’ because we observe every single city in both the year 2000 and 2001. This result remains true for unbalanced panels since Q is still the orthogonal pro-jection on the matrix of individual dummy variables. We also formally test the degree of similarity between both productivity indices for a given structure of panel data. JEL Classification: C21, C31 Keywords: difference-in-difference estimation, attrition, panel estimation, balanced panel, unbalanced panel Corresponding author: Nov 15, 2020 · So if the time range of data of a country is a subset of 1996~2006, then this country should be dropped, while those whose time range equals or is larger than 1996~2006 should be kept, and the final result should be a balanced panel. You should ensure that you have random attrition in your panel, i. The methodology requires that you observe your dependent variables in every period. I use Stata 12. disebut balanced panel. I am aware that it is okay to have unbalanced data to run regressions. , the second one above) is one in which at least one member of the panel is not observed every time. Apr 4, 2011 · This work aimed at presenting a faster general algorithm for estimation of panel data models with two fixed effects, when it is compared with PROC PANEL, working with balanced or unbalanced data. When a balanced set is needed (in order to reduce the file size or send it to others), I would use Stata or R and never do it from individual and time characteristics. Oct 20, 2023 · Yes, you have a balanced panel by construction, but you are actually missing values in your dependent variable. In the example that follows, we will be working with a dataset of United States (US) foreign aid disbursements to all African countries for the 2001-2017 period. An unbalanced panel (e. Oct 11, 2016 · I have unbalanced panel with gaps xtset coid year panel variable: coid (unbalanced) time variable: year, 1990 to 2015, but with gaps delta: 1 unit I know following command will give me balanced Panel with 15 years by coid: gen nyear=[_N] keep if nyear == 15 We can distinguish between balanced and unbalanced panels. EM algorithm can use the conditional mean to make an educated guess (i. We In fact, you do not want to create a balanced sample from existing data (this is what you did with your code above), but you would like to extend your sample with all possible combination of STATE and PERIOD. If the panel datasets are unbalanced they may need to be condensed to include only the consecutive periods In this example, firms 1 and 2 have data available for all three years (2020, 2021 and 2022), making it a balanced panel data. I have missing observations for some states in some years prior to 2014 and after 2014. This can arise from various factors, such as missing data, different entry and exit times of subjects in the study, or the nature of the data collection process Dec 3, 2018 · I compiled an unbalanced panel dataset, which includes six years from 2010 to 2015. This paper surveys the econometrics literature on unbalanced panels. Ask Question Asked 10 years, 6 months ago. Understanding the type of panel data being used is crucial for selecting the appropriate regression model and ensuring accurate results. h. Karakteristik orang 1 dan orang 2 dikumpulkan pada tahun 2013 dan 2014, tetapi orang 3 hanya diamati pada tahun 2014, bukan tahun 2013 dan 2014. frame is a balanced panel, the second is an unbalanced one: the first data. If some of the omitted variables you hope to capture in the changes analysis vary over time, then the estimator and more. Jun 13, 2024 · My problem is that I have unbalanced panels - for some units, also those treated, I don't have full observations in the post period. MVREGRESS does not have any indicator variable for indexing the unbalanced panel data, so the workaround is to make the data artificially balanced. frames that i would like to merge and turn into a panel. For running a certain command I need to make my data balanced panel. Consequently, if a balanced panel contains panel members and periods, the number of observations in the dataset is necessarily =. Balanced data is preferred over unbalanced panels, because it allows an observation of the same unit (e. ROA is return on asset, which was measured at firm level. Dec 13, 2024 · Panel data structures vary, each with distinct characteristics and further implications for analysis. Data data and shp files Reproducible ex May 31, 2020 · I came across this definition of a "strongly balanced" panel: "When the dataset contains a time variable, panels are said to be strongly balanced if each panel contains the same time points, weakly balanced if each panel contains the same number of observations but not the same time points, and unbalanced otherwise. I created ny1 and t1 to remove the gaps. Balanced: all individuals are observed in all time periods; Unbalanced: all individuals are not observed in all time periods. yqsk pyc yzwh gjifk ndbc gdjv khq kod duql vxacp vkxqeh suzeepil zbaj kbk gbcl