Vol. LVI (2015) PL ISSN 0071-674X
INCOM E OF H O U SE H O LD MEMBERS IN P O L A N D
PAWE Ł ULMAN
Cracow University of Economics, D epartm ent of Statistics1
e-mail: ulmanp@uek.krakow.pl
STRESZCZENIE
P. Ulman. Dochody członków gospodarstw domowych w Polsce. Folia O econom ica Cracoviensia 2015, 56: 23-34.
Poziom d o ch o d ó w go sp o d arstw dom o w y ch w p ły w a nie tylko n a zaspokojenie in d y w id u a ln y ch p o trzeb ich członków, ale ró w n ież zap ew n ia o d p o w ied n i sta n d a rd życia gospodarstw a. Z tego w zg lęd u w ielu badaczy w yk azu je zainteresow anie analizam i d o ch o d ó w go sp o d arstw dom ow ych. W artykule p o d ję to tem atykę kształtow ania się d o ch o d ó w członków go sp o d arstw dom ow ych. N a p o d staw ie in d y w id u a ln y ch d a n y c h o d o ch o d ach m ożliw ą staje się analiza stru k tu ry źródeł dochodów , k ształtujących ogólny doch ó d badanej osoby.
C elem p ra c y je st p re z e n ta c ja ro z m ia ru i ź ró d e ł d o c h o d ó w lu d n o ś c i Polski w ró ż n y c h p rz e k ro ja c h b ad an ej zbiorow ości. D ane staty sty czn e zostały z a czerp n ięte z Badania Budżetów Gospodarstw Domowych p rz e p ro w a d z o n e g o p rz e z GUS w 2011 r. Zbiór d a n y c h zaw ierał 37375 obserw acji go sp o d arstw i p o n a d 100 tys. rekordów , zaw ierających inform acje o in d y w id u a ln y ch osobach. W celu p o ró w n a n ia ro zk ład ó w d o ch o d ó w w y k o rzy stan e zostały m o d ele teoretyczne ty c h ro zk ład ó w z u zm ie n n io n y m i p ara m e tra m i, w szczególności zasto so w an o ro zk ład B urra ty p u XII. Ponadto w y k orzystano regresję kw an ty lo w ą dla identyfikacji d e te rm in a n t d o chodów in d y w id u a ln y c h członków g o spodarstw dom ow ych.
ABSTRACT
The size of h o u seh o ld s incom e determ in es n o t m erely th e deg ree of satisfaction of indiv id u al n e e d s b u t also ensures h o u seh o ld s' ad e q u a te social status. It causes a n in terest m a n y researchers in analysis of h o u seh o ld s incom e. The subject of th e stu d y is th e in d iv id u al incom e of th e each m em ber of h o u seh o ld . W h e n analysing h o u seh o ld b u d g ets, financial incom e from one m o n th is assigned to in d iv id u al persons. Thus, th e level a n d stru c tu re of in d iv id u a l incom e sources m ay be identified. The incom e of single p erso n s acquired from n u m e ro u s sources form s their in d iv id u al incom e.
1 Publication was financed from funds allocated to Faculty of M anagem ent (Cracow University of Economics) w ithin grants to maintain research capacity.
The p a p e r aim s to show th e size a n d sources of th e Polish p eo p le incom e in th e different cross section of th e analysed sam ple. The statistical in fo rm atio n is d eriv ed from th e h o u seh o ld b u d g e t survey of 2011 th a t is co n d u cted an n u ally by th e C entral Statistical Office of Poland. The en tire set of in d iv id u al observations of h o u seh o ld s constitutes 37,375 records a n d in th e case of h o u seh o ld m em bers — over 100,000 records. In o rd er to com pare incom e d istributions u se is m ade of theoretical m odels of incom e d istrib u tio n w ith variable p aram eters. This a p p ro ach allow s to cap tu re th e im pact of in d iv id u al characteristics o n th e sh ap e of th e d istrib u tio n of incom e an d its descriptive statistics. The theoretical d istrib u tio n B urr XII h as b e e n u se d as a m o d e l of incom e distribution. M oreover q uantile reg ressio n m o d e l are u se d for ide n tificatio n of d ete rm in a n ts of in d iv id u al incom e.
SŁOWA K LU CZO W E — KEY W O RD S
ro zk ład dochodów , m odel regresyjny, źródła d o chodów in d y w id u a ln y ch incom e distribution, reg ressio n m odels, sources of perso n al incom e
1. INTRODUCTION
H o usehold incom e is one of the m ost com m on economic term s. M ost often it is g e n e ra ted th ro u g h basic h u m a n labour, w h ich p rovides for personal needs. For this reason, it has g e n e ra ted m u ch interest in analysing incom e levels a n d its v ariation from p e rso n to person. D. Ricardo a n d T. M alth u s h a d b e g u n discussions reg a rd in g th e allocation of incom e a m o n g different m em bers of society m an y years ago. D. Riccardo analysed th e low level of m in im u m w age in com parison to the large su rplus of labour force available. The risk of pover ty w as similarly in te rp re ted by T. M althus. W hile exam ining the relationship b e tw e en incom e levels a n d p o p u latio n g ro w th , he e n d o rse d a lim itation to th e birth rate, justifying it w ith th e inevitable expansion of poverty. E. Engel c o n d u c te d research on h o u se h o ld incom e in a special way, analysing stati stical b u d g ets of w orkers' families. H e observed a p a tte rn (know n as Engel's law), statin g th a t as h o u se h o ld incom e increases, th e p ro p o rtio n of incom e sp e n t on food decreases, th u s increasing th e p ro p o rtio n of expen d itu res on durable goods a n d services. F u rther on, studies w ere co n d u cted on various aspects of incom e distribution, a n exam ple of w h ich m ay be m easu rin g inco m e inequalities th ro u g h o u t th e com m unity. As early as in 1898, v o n Bortkie wicz p ro p o se d th e m ea n deviation as a m easure of incom e inequality, while C. G ini (1912) p rese n ted one of th e m ost p o p u lar m easures of incom e inequality k n o w n as the the Gini coefficient. In parallel, m eth o d s of describing incom e distribution u sin g m athem atical functions w ere developed. The first one w ho
u se d such a function for m odels of incom e distribution w as V. Pareto. Since
th e n , m a n y m easu res h ave b e e n p ro p o se d to characterise incom e distrib u tion along w ith m an y functions to describe these distributions. Various th e ories w ere also develo p ed w h ich considered th e origin a n d sh ap in g of these distributions.
This p a p e r presents th e issue of incom e, th e source a n d v ariation a m o n g m em bers of Polish households. The analyses of incom e are often b ased on d ata related to h o u se h o ld incom e, w hich introduces certain limitations. The characteristics of individual h o u seh o ld m em bers a n d their contribution to the general incom e of th e h o u seh o ld are th u s om itted. The objective of this p a p e r is to p resen t the level of incom e a n d its variation in different social gro u p s of Polish society. In particular, this differentiation has b een analysed in term s of th e factors w hich sh ap e it, assum ing th a t their effect is n o t identical in different incom e g ro u p s of th e an alysed individuals. The Polish H o u se h o ld B udgets Survey data w ere u se d for a statistical analysis. They are described in short in th e latter p a rt of th e paper. The statistical m eth o d s u sed in this p a p e r are also p rese n ted there. The th ird ch ap ter presents th e results o btained from the co n d u cted analyses, follow ed by conclusions in the final part.
2. MATERIAL AND METHODS
D ata w as retrieved from h o u seh o ld b u d g ets su rv ey (HBS) co n d u cted by the Polish CSO in 2011 a n d w as u se d for analysing individual incom e of h o u se h old m em bers. It is one of th e basic surveys for public statistics in Poland. It has b e e n c o n d u c te d on a co n tin u o u s basis since 1957, alth o u g h its m e th o d a n d scope of execution has b een altered several tim es since its beginning. In recent years, it has p ro v id ed d ata sets for ca. 37,500 h o u seh o ld a n d over 100,000 individuals. From a m o n g th e total n u m b er of Polish h o u seh o ld m em bers, this p a p e r takes into account those at least 18 years of age, brin g in g the n u m b er of total observations to 84,316. D ata reg a rd in g th e incom e a n d characteristics of these individuals w ere acquired in this way. The Burr type XII distribution (or sim ply th e Burr distribution) will be u sed for analysing th e incom e distribution of h o u seh o ld m em bers. It is one of th e tw elve distributions g e n e ra ted by the Burr distribution system , a n d is also k n o w n as the S in g h -M ad d ala distribution; see Kleiber, Kotz (2003). The Burr ty pe III distribution is an o th er distribution in this family, also k n o w n u n d e r th e nam e of th e D ag u m distribution. The p a p e r by M cD onald a n d Xu (1995) p. 139 — includes classification of m ost of th e theoretical distributions u se d for m odelling th e empirical distribution of incom e (wages). U tilizing a tree diagram , th ey p re se n te d th e d e p e n d e n cies b etw een particular distributions, from th e m ost general, 5-param etric beta distributions to one-param eter distributions, e.g. th e x2 distribution. Basing on d ata related to family incom e, th ey co ncluded th a t th e generalised beta type II distribution best approxim ates empirical distributions of income. The D agum distribution p ro v ed to be slightly inferior according to th e u se d statistical ad ju stm ents m easures. B andourian, M cD onald a n d Turley (2003), p. 9 — reach ed similar conclusions ad justin g various incom e distribution m odels for d ata from
23 countries obtained in several one-year periods. They fo u n d th a t th e D agum distribution is m ore favourable for 3-param etric distributions rath e r th a n w h e n u se d for 2-param etric distributions. As c o m p ared w ith th e g eneralised beta type II distribution, it is slightly w orse according to th e ad ju stm en ts n e e d ed to the empirical data, w h ereas th e density function charts of b o th distributions are alm ost identical. The Burr ty p e III distribution (Dagum) a n d Burr ty p e XII distribution (Singh-M addala) are v ery similar (also d u e to th e approxim ation possibilities of empirical distributions) m odels of incom e distribution a n d b o th w ere u se d n u m ero u s tim es to describe the sh a p in g of incom e a n d w ages as indicated by Kleiber Kotz (2003), p. 197-222. For this reason, it w as d ecided to utilize one of these m eth o d s in this p a p e r as a m odel of incom e distribution for individual h o u seh o ld m em bers in Poland.
The cum ulative Burr ty p e XII d istrib u tio n fu n ctio n m ay be d efin e d as follows:
F(y) = 1 - 1/[1 + eayb]c,
w h ere y is incom e, a n d a, b, a n d c refer to distribution p aram eters w hich m ay be estim ated by ML. Some of th e theoretical distribution p aram eters m ay be m ad e a function of th e characteristics of th e stu d ie d u n its (household m em bers). By follow ing this approach, it allows for a m ore th o ro u g h analysis to th e changes in incom e distribution, d e p e n d in g o n th e characteristics of the individuals obtaining this income. As a result, w e have a conditional incom e distribution in term s of individual characteristics. The selection of these "con ditional" param eters is m ade on the basis of statistical criteria on ad ju stin g the m odel to empirical data. M ost often, reliable results can be obtained by m ak in g
p aram eters a a n d b as a function of explanatory variables, w h ich in tu rn allows
for exam ine their im pact o n sh a p in g all distribution descriptives.
To stu d y th e effect of v ariou s factors o n sh a p in g in d iv id u al incom e of h o u se h o ld m em bers, regression m odelling has b een u se d b ased on so-called quantile regression. A lthough it w as p ro p o se d by Koenker a n d Bessett in 1978 (1978), its p opularity came into light in recent years; see Koenker (2000), Koenker, Hallock (2001), Koenker (2005). A quantile regression p roduces a m ore robust p aram eter estim ation w h e n com pared to a traditional regression based on the expected value of the d e p e n d e n t variable. As a m e th o d of ro b u st statistics, it takes into account th e existence of non-typical observations (outliers); m oreover, th e problem of biased estim ation disappears, w h ich in traditional regression m o d ellin g could arise a n d exist w h e n su b -sam p les w ere extracted o n th e basis of incom e criterion. In reference to a classic regression, th e quantile a p p ro a c h allow s for th e expansion of th e analysis of ch an g es in th e value of the d e p e n d e n t variable into m an y points (the quantiles of th e d e p e n d e n t variable) a n d n o t only to th e expected value of this variable. Estim ation of
param eters of a quantile regression has a sem i-param etric n atu re, w h ich allows rejecting prem ises about th e ty pe of distribution for th e residual vector in the m odel. In a general case, quantile regression p aram eters for an y quantile are estim ated by the m inim ization of the w eig h ted su m of th e value of absolute residues according to th e form ula:
The estim ation of several quantiles each tim e for th e w hole sam ple results in several vectors of param eter estim ates (fl). In this way, non-typical (outliers) observations are assigned low er w eights, w hich solve the problem of accounting for th e m in th e m odel. M ost often, s ta n d a rd e rro r of estim ates in quantile regressions are obtained u sin g the boo tstrap m eth o d according to th e G ould approach; see G ould (1992), (1997).
As it has already b een re p o rte d above, results of empirical research p resen ted below w ere obtained o n th e basis of h o u seh o ld b u d g e t su rv ey of 2011. These m ostly refer to incom e of individual h o u seh o ld m em bers of at least 18 years of age. There w ere 84,316 observations. These individuals obtained incom e from th e follow ing sources: hired w o rk (HW), self-em ploym ent oth er th a n a private farm in agriculture a n d free profession (SEMP), p rivate farm in agriculture (AGR), p ro p erty (PRO), p en sio n of a p ro p erty or lan d (REN), social insurance benefits (SIB), o th er social benefits (OSB) a n d o ther sources (OSC). Figure 1 p resen ts th e stru ctu re of sources of incom e of th e stu d ie d individuals cate gorized by their age. The high est share in total incom e of th e p o p u latio n is sh a p e d by tw o sources: h ire d w o rk a n d social insurance benefits. The form er pred o m in ates for individuals below 60 years of age, w h ereas the latter refers to m ore elderly individuals. Incom e from self-em ploym ent o ther th a n a private farm in agriculture a n d free profession (SEMP) a n d private farm in agriculture (AGR) form a relatively unsu bstan tial share of total incom e. The highest value of this share in b o th cases is reco rd ed for perso n s aged 25 to about 50. Thus, tw o sources of incom e are of basic significance for the incom e distribution of th e Polish population: h ired w o rk a n d social insurance benefits, w hich provide alm ost 80% of th e total incom e observed.
n
w here:
for z$ 0
for z < 0 .
100% 9 0% 8 0% 7 0% 6 0% 5 0% 4 0% 3 0% 2 0% 1 0% 0% 1 8 - 2 4 2 5- 29 3 0 - 3 4 3 5 - 3 9 4 0 - 4 4 4 5 - 4 9 5 0 - 5 4 5 5 - 5 9 6 0 - 6 4 6 5 - 6 9 7 0 - 7 4 7 5+ ■ H W « S E M P I A G R B P R O + R E N « S I B I O S B * O S C
Figure 1. The stru ctu re of th e in d iv id u al incom e from different sources categorized b y th e ir age (in %) — Poland 2011
In discussion of th e average level of incom e from th e above sources, it sh o u ld be m en tio n ed th a t th e h ig hest average incom e is generally obtained by individuals aged 35-39. The m ain source of incom e is obtained th ro u g h h ired w ork a n d self-em ploym ent. A basic decrease in th e average incom e from w ork a n d its share in total incom e is rep o rted for individuals over th e age of 50. These individuals often enjoyed th e privilege of early retirem en t or w ere p ro v id ed g ro u n d s to be aw a rd ed p en sio n benefits, especially w h e n a job is lost. Some research exam ples sh o w th at for elderly individuals, th e loss of w o rk results in a m ore difficult task of once again b ein g em ployed. Thus, th e alternative solution is th e possibility of obtaining social benefits. Said individuals often decide to term in ate professional activity entirely.
The level a n d stru ctu re of th e obtained incom e also varies by gender. The average general incom e of m en is 45% h ig h er th a n th a t observed for w om en. In particular, incom e of w o m en is clearly low er in b o th h ire d w ork a n d self em ploym ent, w hile in th e case, generally speaking, u n e a rn e d sources w o m en have got h igher incom e on average. The share of incom e from w o rk com prising of total incom e for m en is alm ost 68%, w hile for w o m en this share is about 55%. It w as observed th a t w o m en clearly h av e a h ig h er share of incom e obtained from social insurance, w h ich is m ostly a result of a relatively larger n u m b er of w o m en at or above pen sio n age.
The size of th e location w h ere th e stu d ie d individuals reside is directly co nnected w ith th e variation of th e average incom e. This incom e is m ostly o btained th ro u g h h ired w o rk a n d self-em ploym ent. Its share of total incom e a m o u n ted to 72% in cities a n d alm ost 51% in ru ral areas. The ratio of the average incom e for resid ents of large cities to those in th e ru ral areas in Poland in 2011
w as 1.46. The h ig h er p ortions of total incom e for resid en ts in ru ra l areas w ere rep o rted from agriculture activities (20.7%) a n d o th er social benefits (3.2%).
O n average, m a rrie d w o m e n re p o rt low er incom e th a n single w o m en , w hereas th e situation in is reversed for m en. The com parison of incom e for w ives a n d h u sb a n d s show s th at th e average incom e of m en is significantly h ig h er th a n th a t of w o m e n (by a b o u t 66%), w hile th e stru ctu re of incom e sources rem ains quite similar for b o th genders. M en are slightly m ore prev alen t reg a rd in g incom e obtained th ro u g h self-em ploym ent, w hereas w o m en prevail from other social benefits. S tudying th e differentiation of incom e for m en an d w o m en is an interestin g research issue related to th e changes in social roles of b o th m en a n d w o m en in m o d e rn societies. The analysis of this problem in th e context of costs a n d benefits in ho u seh o ld s w o u ld allow for an assessm ent of economic effectiveness of th e given family m odel. H ow ever, assessm ent of som e elem ents of said costs a n d benefits is certainly difficult to say th e least.
Figure 2 presents th e Burr ty p e XII density function for th ree cases: total incom e, incom e from h ired w o rk a n d incom e from social insurance benefits. The param eters of these distributions have b een estim ated w ith th e ML u sin g GRETL. All th e estim ates p ro v ed to be statistically significantly different from zero. The figure clearly show s the difference b etw een the distribution of incom e from h ire d w o rk a n d th e distribution of incom e from social insurance. The distribution of incom e from h ired w o rk is skew ed to w ard s h ig h er values an d dem onstrates m ore variation of incom e in reference to the distribution of income from social insurance. The d istrib utio n of incom e is largely d e te rm in e d b y th a t obtained th ro u g h h ire d work. That bein g said, its sh ap e is similar to the distribution of incom e from this source rath e r th a n to th a t from social insurance. The p ro p o rtio n of incom e obtained from h ire d w o rk o u t of total incom e is ca. 54%, w hereas social insurance incom e is about 25%.
The above o b serv atio n s are c o n firm e d in d escrip tiv es of th e stu d ie d distributions (see Table 1): th e average incom e from h ired w o rk is significantly h ig h er th a n incom e from social insurance. It is in terestin g to n o te th a t the m ed ian a n d m ost frequen t incom e show s a lesser variation in b o th absolute a n d relative view s. This analysis ind icates less in eq u ality of incom e from social insurance th a n from h ire d work. All th e utilized m easures of incom e inequality confirm this observation. It is interestin g to n o te th a t distribution of total incom e is m ost strongly differentiated d u e to th e fact th a t th e total incom e is obtained from various sources w h ich contain their o w n individual internal level of inequality. M oreover, th e su m m ary of this incom e additionally g en erates a ran g e of inequalities resu ltin g from th e differences in sh a p in g incom e from v ario u s sources. A sym m etry of d istrib u tio n s is rig h t-sk ew ed , w hereas a abbreviated m easure of welfare (the Sen index) show s th a t incom e from h ire d w o rk generates h ig h er levels of w elfare th a n incom e from social insurance.
Income distributions - Burr 12 0.0010 0.0008 0,0006 > '51 C <b * a 0.0004 0,0002 0,0000 0 1000 20 0 0 3000 4 0 0 0 5000 60 0 0 7000 Income (PLZ)
Figure 2. Incom e distributions (Burr XII) — selected sources of incom e
Table 1
D escriptives of th e selected incom e distributions o n th e base B urr XII distrib u tio n (in Polish zl)
Total incom e H ired w o rk incom e Social insurance benefits
Average 1849.9 2046.4 1309.3
M edian 1494.2 1748.3 1157.8
M ode 1100.5 1424.2 1001.0
C oefficient of variation 0.8612 0.6940 0.5772
Relative average deviatio n 0.2603 0.2202 0.1860
Skew ness 0.4704 0.4382 0.4080
G ini 0.3675 0.3130 0.2656
The discussion of the m eth o d s includes th e com m ent th a t analysis of incom e distribution m ay be exten d ed w ith the assum ption th a t som e p aram eters will becom e functions of characteristics of th e analysed individual. It w as decided th a t b o th param eters a a n d b will d e p e n d on: th e level of education m easu red on four levels (basic, basic vocational, secondary a n d higher, w ith basic education u se d as the reference level); the place of residence of th e analysed individual m ea su re d in th re e categories (large city, sm all a n d m ed iu m -size cities a n d villages, w ith individuals resid in g in ru ral areas u se d as th e reference category); g e n d e r (a binary variable w ith fem ale as the reference category); a n d th e age of th e analysed individuals in years. The p ro ced u re for estim ating th e param eters of th e m odel w o u ld p ro v id e statistically significant values. Table 2 p resen ts conditional characteristics of distribution of incom e from th e sources researched earlier a n d incom e from self-em ploym ent d e p e n d in g o n gender. It has b een assum ed th a t th e analysed individual lives in a large city, has h ig h er education a n d is 35 years old in the case of incom e obtained from w ork, a n d 70 years old in th e case of incom e obtained from social insurance.
The obtained results confirm th e differentiation of incom e for individual p e rso n s b y gender, w ith th e sm allest ran g e fo u n d in incom e from social insurance. O n average the h igh est level of incom e applies to self-em ployed individuals. It is interestin g to no te th a t w o m en in this case achieve an average incom e at th e level similar to th e average incom e of m en obtained from h ired work. The individuals obtaining incom e from self-em ploym ent are certainly characterized by the largest inequalities of incom e levels, w hich results in relative equalisation of the values of the Sen index b etw een th e incom es from b o th types of work. This index takes into consideration the average level of incom e an d th e level of incom e inequalities m easu red by th e Gini coefficient. A g ro w th in th e value of th e average increases th e value of the Sen index, w h ereas a g ro w th in the level of inequalities red u ces the value of th e said index.
Table 3 p resen ts th e results of estim atin g th e quantile regression m odel for th e n a tu ra l lo garith m of incom e from th re e sources: h ire d w ork, self em p lo y m en t a n d social insurance. Three basic factors have b een tak en into account th a t m ostly d eterm in e incom e from w ork, i.e. age, g en d e r a n d level of education. For age, an additional variable has also b een u se d — th e square of age, w ith th e objective of cap tu rin g non-linearity of incom e to age relationships according to th e th eo ry of w ages a n d age profiles. It assum es th a t th e average incom e from w o rk (wages) increases w ith age u p to a certain level a n d decreases in th e case of older individuals. The g e n d e r variable is by d efault a b in ary variable w ith a fem ale reference category. In ord er to describe the relationship of incom e a n d education, a binary variable set has b een u se d (Educ2-Educ4) w hich refer to basic vocational, seco nd ary a n d h ig h er education, respectively. Basic education is the reference category.
Table 2
D escriptives of th e selected conditional incom e distributions o n th e base B urr XII distribution
H ired w o rk incom e Self-em ploym ent incom e Social insurance benefits M an W om an M an W om an M an W om an Average 2853.0 1968.9 3706.2 2822.9 2121.8 1901.7 M edian 2534.4 1769.4 3001.0 2217.2 1954.9 1762.9 M ode 2142.6 1522.4 1934.4 1443.5 1776.2 1611.6 C oefficient of variation 0.5828 0.5499 0.8058 0.9000 0.4352 0.4175
Relative average deviatio n 0.2016 0.1925 0.2792 0.2862 0.1484 0.1441
Skew ness 0.4272 0.4124 0.5933 0.5429 0.3743 0.3653
G ini 0.2867 0.2741 0.3907 0.4014 0.2127 0.2067
Sen index 2035.1 1429.2 2258.2 1689.8 1670.5 1508.6
The com plete estimates of the param eters p ro v ed to be statistically significant even for the squ ared age variable, in th e case of w h ich th e estim ate for incom e from social insurance p ro v ed to at a v ery low level. This show s th a t this incom e has alm ost a linear course in reference to age. It is also interestin g to observe th e levels of th e constan t value for various quantiles, especially in the case of incom e from self-em ploym ent. These values are clearly varied here, especially in th e first a n d th ird quartiles. This situation indicates a h ig h level of variation in incom e from this source, w h ich is also fo u n d in Table 2. H ow ever, on the other h a n d , this variation is co m p en sated w ith a h ig h er positive effect of individual characteristics of th e analysed individuals o n incom e from self-em ploym ent in th e regression m odel d e te rm in e d for th e 25th quantile in reference to th e 75th quantile m odel, w h ich is expressed in estim ates of p aram eters of these models.
In all cases, w om en obtain low er income. At the sam e time, the difference grow s w ith an increase in income class from both hired w ork an d social insurance. In the case of incom e from self-em ploym ent, the largest variation in incom e in term s of gender is fo und in the lowest incom e class. It is also interesting to note th at a variation in incom e in this approach is n o t uniform in term s of the source of income. W omen are often observed b eh in d m en in the case of income from self-em ploym ent an d ahead for incom e from social insurance. The problem of incom e (wages) variation for m en a n d w o m en is one of m ore im portant research issues in w hich the possibility of discrim ination of w o m en is often analysed.
The education level of individual perso n s is an im p o rtan t factor th a t affects incom e. The results p rese n ted in Table 3 clearly sh o w th a t incom e grow s w ith the increase in the level of education. The m ost significant increases are observed
in th e case of incom e from self-em ploym ent a n d , similar to th a t of th e g en d er variable, decreases as th e incom e class progresses. In the case of incom e from h ire d w o rk a n d social insurance, the inter-quartile variation is relatively small. The above results sh o w th a t variation in the total incom e of th e society has different sources w h ich generate inequalities in the distribution of incom e w ith v arie d strength . For this reaso n , chan ges in th e stru ctu re of th e sources of incom e m ay result in changes in th e level of incom e inequalities for th e total population, even w h e n th e level of inequalities g e n e ra ted in th e distributions of incom e from individual sources does n o t increase.
Table 3 The outcom es of quantile regression for selected incom e
Incom e Q uantile Const. Age sq Age Sex Educ2 Educ3 Educ4
H ir ed w o rk 25th 4.6874 0.0971 -0.0011 0.2948 0.2376 0.4048 0.7519 50th 5.3627 0.0761 -0.0009 0.3231 0.1470 0.3418 0.7099 75th 5.5926 0.0749 -0.0008 0.3749 0.1409 0.3504 0.7843 S e lf e m -p lo y m e n t 25th 3.2093 0.1333 -0.0015 0.4709 0.6677 0.8452 1.1531 50th 4.5826 0.1034 -0.0012 0.3585 0.4654 0.6570 0.9406 75th 5.6154 0.0833 -0.0010 0.3525 0.2575 0.4807 0.7998 S o c ia l in s u ra n c e 25th 4.9727 0.0339 -0.0002 0.1418 0.1419 0.3554 0.6827 50th 5.4350 0.0273 -0.0001 0.2257 0.1926 0.4071 0.6885 75th 6.0891 0.0191 -0.0000 0.3010 0.1661 0.3593 0.6346 4. CONCLUSION
Research of social p h e n o m e n a requires co n tin u o u s actualization. This is d u e to dynam ic changes in b o th th e analysed p h e n o m e n o n a n d th e im pact of the su rro u n d in g s w ith in w h ich th e p h e n o m e n o n is analysed. H o u seh o ld incom e is such a p h e n o m e n o n a n d has m an y research studies d ev o ted to it. D espite this, its n atu re has n o t b een th o ro u g h ly explained.
The p a p e r presents th e results of th e research on th e sh ap in g of incom e of household m em bers in Poland, w hose level has significantly increased, especially after Poland join ed th e E u ro p ean U nion. Incom e of th e Polish p o p u latio n comes m ostly from tw o sources: h ire d w o rk (ca. 54%) a n d social insurance (ca. 25%). The largest average level of incom e from h ire d w o rk w as observed for persons
aged 35-39, w hereas perso ns of over 60 years of age obtained th eir m ain source of incom e from social insurance. W hile an aly sin g v ario u s social g ro u p s of individuals inclu d ed in th e study, incom e m ay be sh o w n as differing in b o th th e level a n d th e stru ctu re of sources as a resu lt of gender, place of residence a n d m arital status. Studying the variation of incom e in different hou seh o ld types d u e to their dem ographic com position m ay brin g about interesting observations in the context of evolving social roles of b o th m en a n d w om en. H ow ever, such discussions w o u ld require special statistical research.
It is also interesting to note th a t the distribution of incom e from different sources differs n o t only w ith the level of average values, b u t also w ith th e level of incom e inequality in these distributions. This th e n poses the question of the origins of incom e inequalities in th e given society, w hich m ay in p a rt be d u e to changes in th e stru cture of incom e sources. Thus, assum ing an increase in th e n u m b er of elderly people in th e society w ho receive incom e from social benefits, one m ay believe th a t the general level of incom e inequality will be low er d u e to a sm aller v ariation in incom e from this source. O n th e oth er h a n d , these tre n d s c an n ot be foreseen in research of social p h e n o m e n a n o t only w ith certainty, b u t even w ith h ig h probability.
The application of a quantile regression allow ed fin d in g th e relationships be tw e en incom e from various incom e classes a n d th e select characteristics of th e stu d ied individuals. It tu rn s ou t th a t the effect of these characteristics is n o t u niform for individuals of different incom e levels.
The issues related to incom e in th e popu latio n , alth o u g h stu d ie d for years, continuously brin g about m an y challenges a n d observations.
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