OpenML
Filter results by:
* Dataset Title: AutoUniv Dataset data problem: autoUniv-au7-700 * Abstract: AutoUniv is an advanced data generator for classifications tasks. The aim is to reflect the nuances and heterogeneity of…
4537 runs0 likes7 downloads7 reach19 impact
700 instances - 13 features - 3 classes - 0 missing values
* Abstract: A 3-class version of abalone dataset. * Sources: (a) Original owners of database: Marine Resources Division Marine Research Laboratories - Taroona Department of Primary Industry and…
105 runs0 likes3 downloads3 reach6 impact
4177 instances - 9 features - 3 classes - 0 missing values
A 3-class version of Cardiotocography dataset.
134 runs0 likes13 downloads13 reach6 impact
2126 instances - 36 features - 3 classes - 0 missing values
Datasets of Data And Story Library, project illustrating use of basic statistic methods, converted to arff format by Hakan Kjellerstrand. Source: TunedIT: http://tunedit.org/repo/DASL DASL file…
593 runs0 likes6 downloads6 reach6 impact
478 instances - 11 features - 3 classes - 0 missing values
* Dataset Title: Robot Execution Failures Data Set * Abstract: This dataset contains force and torque measurements on a robot after failure detection. Each failure is characterized by 15 force/torque…
129 runs0 likes3 downloads3 reach5 impact
117 instances - 91 features - 3 classes - 0 missing values
* Dataset Title: Vertebra Column - 3 classes * Abstract: Data set containing values for six biomechanical features used to classify orthopaedic patients into 3 classes (normal, disk hernia or…
154 runs0 likes5 downloads5 reach5 impact
310 instances - 7 features - 3 classes - 0 missing values
* Title: seismic-bumps Data Set * Abstract: The data describe the problem of high energy (higher than 10^4 J) seismic bumps forecasting in a coal mine. Data come from two of longwalls located in a…
152 runs0 likes37 downloads37 reach5 impact
210 instances - 8 features - 3 classes - 0 missing values
* Title: seeds Data Set * Abstract: Measurements of geometrical properties of kernels belonging to three different varieties of wheat. A soft X-ray technique and GRAINS package were used to construct…
190 runs0 likes5 downloads5 reach5 impact
210 instances - 8 features - 3 classes - 0 missing values
Dataset from the MLRR repository: http://axon.cs.byu.edu:5000/
731 runs0 likes5 downloads5 reach13 impact
151 instances - 7 features - 3 classes - 0 missing values
Dataset from the MLRR repository: http://axon.cs.byu.edu:5000/
153 runs0 likes8 downloads8 reach6 impact
81 instances - 13 features - 3 classes - 0 missing values
analcatdata A collection of data sets used in the book "Analyzing Categorical Data," by Jeffrey S. Simonoff, Springer-Verlag, New York, 2003. The submission consists of a zip file containing two…
41 runs0 likes2 downloads2 reach7 impact
1340 instances - 18 features - 3 classes - 20 missing values
The Committee on Statistical Graphics of the American Statistical Association (ASA) invites you to participate in its Second (1983) Exposition of Statistical Graphics Technology. The purposes of the…
164 runs0 likes3 downloads3 reach6 impact
406 instances - 9 features - 3 classes - 14 missing values
analcatdata A collection of data sets used in the book "Analyzing Categorical Data," by Jeffrey S. Simonoff, Springer-Verlag, New York, 2003. The submission consists of a zip file containing two…
35 runs0 likes2 downloads2 reach6 impact
23 instances - 6 features - 3 classes - 0 missing values
Jarkko Salojarvi, Kai Puolamaki, Jaana Simola, Lauri Kovanen, Ilpo Kojo, Samuel Kaski. Inferring Relevance from Eye Movements: Feature Extraction. Helsinki University of Technology, Publications in…
440 runs0 likes10 downloads10 reach7 impact
10936 instances - 28 features - 3 classes - 0 missing values
1. Title: Contraceptive Method Choice 2. Sources: (a) Origin: This dataset is a subset of the 1987 National Indonesia Contraceptive Prevalence Survey (b) Creator: Tjen-Sien Lim (limt@stat.wisc.edu)…
23111 runs0 likes19 downloads19 reach1 impact
1473 instances - 10 features - 3 classes - 0 missing values
This data set was generated to model psychological experimental results. Each example is classified as having the balance scale tip to the right, tip to the left, or be balanced. The attributes are…
26795 runs2 likes15 downloads17 reach3 impact
625 instances - 5 features - 3 classes - 0 missing values
Squash Harvest Unstored Data source: Winna Harvey Crop and Food Research, Christchurch, New Zealand The purpose of the research was to determine the changes taking place in squash fruit during the…
876 runs0 likes4 downloads4 reach7 impact
52 instances - 24 features - 3 classes - 39 missing values
1. Title: Postoperative Patient Data 2. Source Information: -- Creators: Sharon Summers, School of Nursing, University of Kansas Medical Center, Kansas City, KS 66160 Linda Woolery, School of Nursing,…
1758 runs0 likes9 downloads9 reach1 impact
90 instances - 9 features - 3 classes - 3 missing values
Database of baseball players and play statistics, including 'Games_played', 'At_bats', 'Runs', 'Hits', 'Doubles', 'Triples', 'Home_runs', 'RBIs', 'Walks', 'Strikeouts', 'Batting_average',…
795 runs0 likes10 downloads10 reach2 impact
1340 instances - 18 features - 3 classes - 20 missing values
No data.
1038 runs0 likes8 downloads8 reach1 impact
55296 instances - 10 features - 3 classes - 0 missing values
1. Title: Lung Cancer Data 2. Source Information: - Data was published in : Hong, Z.Q. and Yang, J.Y. "Optimal Discriminant Plane for a Small Number of Samples and Design Method of Classifier on the…
1238 runs0 likes17 downloads17 reach2 impact
32 instances - 57 features - 3 classes - 5 missing values
Primate splice-junction gene sequences (DNA) with associated imperfect domain theory. Splice junctions are points on a DNA sequence at which 'superfluous' DNA is removed during the process of protein…
22842 runs1 likes14 downloads15 reach1 impact
3190 instances - 61 features - 3 classes - 0 missing values
1. Title: Teaching Assistant Evaluation 2. Sources: (a) Collector: Wei-Yin Loh (Department of Statistics, UW-Madison) (b) Donor: Tjen-Sien Lim (limt@stat.wisc.edu) (b) Date: June 7, 1997 3. Past…
2028 runs0 likes12 downloads12 reach1 impact
151 instances - 6 features - 3 classes - 0 missing values
Generator generating 3 classes of waves. Each class is generated from a combination of 2 of 3 "base" waves. For details, see Breiman,L., Friedman,J.H., Olshen,R.A., and Stone,C.J. (1984).…
19670 runs1 likes53 downloads54 reach2 impact
5000 instances - 41 features - 3 classes - 0 missing values
No data.
960 runs0 likes8 downloads8 reach1 impact
55296 instances - 10 features - 3 classes - 0 missing values
Hayes-Roth Database This is a merged version of the separate train and test set which are usually distributed. On OpenML this train-test split can be found as one of the possible tasks. Source…
380 runs0 likes3 downloads3 reach16 impact
160 instances - 5 features - 3 classes - 0 missing values
Pasture Production Data source: Dave Barker AgResearch Grasslands, Palmerston North, New Zealand The objective was to predict pasture production from a variety of biophysical factors. Vegetation and…
878 runs0 likes6 downloads6 reach7 impact
36 instances - 23 features - 3 classes - 0 missing values
Squash Harvest Stored Data source: Winna Harvey Crop and Food Research, Christchurch, New Zealand The purpose of the research was to determine the changes taking place in squash fruit during the…
867 runs0 likes4 downloads4 reach7 impact
52 instances - 25 features - 3 classes - 7 missing values
1. Title of Database: Wine recognition data Updated Sept 21, 1998 by C.Blake : Added attribute information 2. Sources: (a) Forina, M. et al, PARVUS - An Extendible Package for Data Exploration,…
1182 runs1 likes18 downloads19 reach2 impact
178 instances - 14 features - 3 classes - 0 missing values
This is perhaps the best known database to be found in the pattern recognition literature. Fisher's paper is a classic in the field and is referenced frequently to this day. (See Duda & Hart, for…
8061 runs8 likes112 downloads120 reach3 impact
150 instances - 5 features - 3 classes - 0 missing values
### Description ### This dataset is part of a collection datasets based on the game "Jungle Chess" (a.k.a. Dou Shou Qi). For a description of the rules, please refer to the paper (link attached). The…
11 runs0 likes1 downloads1 reach3 impact
44819 instances - 47 features - 3 classes - 10584 missing values
Iris DataSet
0 runs0 likes0 downloads0 reach0 impact
150 instances - 5 features - 3 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
78 runs0 likes2 downloads2 reach6 impact
130 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
72 runs1 likes6 downloads7 reach8 impact
1545 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
78 runs0 likes2 downloads2 reach7 impact
363 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
77 runs0 likes2 downloads2 reach7 impact
329 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
2841 runs0 likes3 downloads3 reach16 impact
630 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
59 runs0 likes6 downloads6 reach8 impact
1545 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
77 runs0 likes3 downloads3 reach7 impact
337 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
65 runs0 likes3 downloads3 reach7 impact
468 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
67 runs0 likes1 downloads1 reach7 impact
458 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
65 runs0 likes3 downloads3 reach7 impact
470 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
77 runs0 likes3 downloads3 reach7 impact
193 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
77 runs0 likes2 downloads2 reach7 impact
203 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
65 runs0 likes2 downloads2 reach7 impact
347 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
2855 runs0 likes4 downloads4 reach16 impact
1545 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
77 runs0 likes3 downloads3 reach7 impact
355 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
77 runs0 likes4 downloads4 reach7 impact
250 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
2866 runs0 likes6 downloads6 reach16 impact
546 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
2862 runs0 likes5 downloads5 reach16 impact
1545 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
2849 runs0 likes5 downloads5 reach16 impact
1545 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
65 runs0 likes2 downloads2 reach7 impact
324 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
77 runs0 likes2 downloads2 reach7 impact
413 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
80 runs0 likes5 downloads5 reach7 impact
405 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
77 runs0 likes2 downloads2 reach7 impact
201 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
65 runs0 likes2 downloads2 reach6 impact
146 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
65 runs0 likes2 downloads2 reach7 impact
412 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
78 runs0 likes3 downloads3 reach7 impact
421 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
2865 runs1 likes18 downloads19 reach16 impact
1545 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
77 runs0 likes2 downloads2 reach7 impact
384 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
2853 runs1 likes7 downloads8 reach16 impact
1545 instances - 10937 features - 2 classes - 0 missing values
The KDD Cup 2009 offers the opportunity to work on large marketing databases from the French Telecom company Orange to predict the propensity of customers to switch provider (churn). Churn (wikipedia…
10982 runs0 likes15 downloads15 reach17 impact
50000 instances - 231 features - 2 classes - 8024152 missing values
Datasets from ACM KDD Cup (http://www.sigkdd.org/kddcup/index.php) KDD Cup 2009 http://www.kddcup-orange.com Converted to ARFF format by TunedIT Customer Relationship Management (CRM) is a key element…
11301 runs0 likes12 downloads12 reach17 impact
50000 instances - 231 features - 2 classes - 8024152 missing values
ARCENE's task is to distinguish cancer versus normal patterns from mass-spectrometric data. This is a two-class classification problem with continuous input variables. This dataset is one of 5…
17 runs0 likes8 downloads8 reach6 impact
200 instances - 10001 features - 2 classes - 0 missing values
Kung chi
1 runs0 likes4 downloads4 reach4 impact
123 instances - 40 features - 2 classes - 0 missing values
knugget chase 3
0 runs0 likes2 downloads2 reach4 impact
194 instances - 40 features - 2 classes - 0 missing values
Mind Cave 2
0 runs0 likes3 downloads3 reach3 impact
125 instances - 40 features - 2 classes - 0 missing values
#### Abstract: MADELON is an artificial dataset, which was part of the NIPS 2003 feature selection challenge. This is a two-class classification problem with continuous input variables. The difficulty…
98021 runs0 likes17 downloads17 reach18 impact
2600 instances - 501 features - 2 classes - 0 missing values
The datasets contains transactions made by credit cards in September 2013 by european cardholders. This dataset present transactions that occurred in two days, where we have 492 frauds out of 284,807…
355 runs0 likes54 downloads54 reach11 impact
284807 instances - 31 features - 2 classes - 0 missing values
This is a corrected version of the previous data file in version 1, which contained a dataset (349 instances) incorrectly merged from the original training and test sets available on UCI (there are…
0 runs0 likes2 downloads2 reach4 impact
267 instances - 45 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
2834 runs0 likes4 downloads4 reach16 impact
1545 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
79 runs0 likes2 downloads2 reach7 impact
322 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
65 runs0 likes1 downloads1 reach7 impact
185 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
2855 runs0 likes8 downloads8 reach16 impact
542 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
2862 runs0 likes7 downloads7 reach16 impact
1545 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
65 runs0 likes3 downloads3 reach6 impact
138 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
65 runs0 likes3 downloads3 reach7 impact
267 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
77 runs0 likes3 downloads3 reach7 impact
484 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
76 runs0 likes4 downloads4 reach7 impact
187 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
66 runs0 likes2 downloads2 reach7 impact
195 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
77 runs0 likes4 downloads4 reach7 impact
275 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
65 runs0 likes1 downloads1 reach7 impact
321 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
2860 runs0 likes5 downloads5 reach16 impact
604 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
66 runs0 likes3 downloads3 reach7 impact
259 instances - 10937 features - 2 classes - 0 missing values
GEMLeR provides a collection of gene expression datasets that can be used for benchmarking gene expression oriented machine learning algorithms. They can be used for estimation of different quality…
65 runs0 likes1 downloads1 reach7 impact
410 instances - 10937 features - 2 classes - 0 missing values
No data.
43 runs0 likes2 downloads2 reach1 impact
1000000 instances - 45 features - 2 classes - 0 missing values
No data.
44 runs0 likes3 downloads3 reach2 impact
1000000 instances - 15 features - 2 classes - 0 missing values
No data.
90 runs2 likes3 downloads5 reach2 impact
663552 instances - 13 features - 2 classes - 0 missing values
No data.
45 runs0 likes2 downloads2 reach1 impact
1000000 instances - 23 features - 2 classes - 0 missing values
Binarized version of the original data set (see version 1). It converts the numeric target feature to a two-class nominal target feature by computing the mean and classifying all instances with a…
1078 runs0 likes11 downloads11 reach6 impact
108 instances - 8 features - 2 classes - 0 missing values
Datasets from the Agnostic Learning vs. Prior Knowledge Challenge (http://www.agnostic.inf.ethz.ch) Dataset from: http://www.agnostic.inf.ethz.ch/datasets.php Modified by TunedIT (converted to ARFF…
778 runs0 likes8 downloads8 reach8 impact
4562 instances - 15 features - 2 classes - 88 missing values
Datasets from the Agnostic Learning vs. Prior Knowledge Challenge (http://www.agnostic.inf.ethz.ch) Dataset from: http://www.agnostic.inf.ethz.ch/datasets.php Modified by TunedIT (converted to ARFF…
406 runs1 likes11 downloads12 reach8 impact
4229 instances - 1618 features - 2 classes - 0 missing values
Binarized version of the original data set (see version 1). The multi-class target feature is converted to a two-class nominal target feature by re-labeling the majority class as positive ('P') and…
131 runs1 likes9 downloads10 reach7 impact
990 instances - 14 features - 2 classes - 0 missing values
* Title: Skin Segmentation Data Set * Abstract: The Skin Segmentation dataset is constructed over B, G, R color space. Skin and Nonskin dataset is generated using skin textures from face images of…
15 runs1 likes10 downloads11 reach6 impact
245057 instances - 4 features - 2 classes - 0 missing values
Data from the RSCTC 2010 Discovery Challenge. All datasets contain between 100 and 400 samples, characterized by values of 20,000 - 65,000 attributes. Samples are assigned to several (2-10) classes.…
48 runs0 likes5 downloads5 reach7 impact
159 instances - 61360 features - 2 classes - 0 missing values
No data.
28 runs0 likes1 downloads1 reach2 impact
1000000 instances - 37 features - 2 classes - 0 missing values
No data.
28 runs0 likes1 downloads1 reach2 impact
1000000 instances - 37 features - 2 classes - 0 missing values
No data.
29 runs0 likes2 downloads2 reach2 impact
1000000 instances - 37 features - 2 classes - 0 missing values
No data.
28 runs0 likes1 downloads1 reach2 impact
1000000 instances - 37 features - 2 classes - 0 missing values
No data.
29 runs0 likes1 downloads1 reach2 impact
1000000 instances - 37 features - 2 classes - 0 missing values